Piezoelectric element and method for manufacturing the same

文档序号：51505 发布日期：2021-09-28 浏览：51次中文

阅读说明：本技术 压电元件及其制造方法 (Piezoelectric element and method for manufacturing the same ) 是由波多野桂一塚越功一于 2021-03-09 设计创作，主要内容包括：本发明的技术问题在于以低成本提供使用了碱金属铌酸系的压电陶瓷的层叠型压电元件。本发明的技术方案为由银的含量为80质量％以上的金属形成内部电极,并且由以具有钙钛矿型结构的碱金属铌酸盐为主成分且含有选自钙和钡中的至少1种碱土金属元素和银的压电陶瓷构成压电陶瓷层,在将上述碱金属铌酸盐的B位点中的元素的含量设为100摩尔％时,上述碱土金属元素的合计含量设为0.2摩尔％以上且低于2.0摩尔％,该压电陶瓷层含有至少1个内包银偏析区域(42)的烧结颗粒(41),并且上述银偏析区域(42)的长径设为10nm以下。(The present invention addresses the problem of providing a multilayer piezoelectric element using an alkali-niobate-based piezoelectric ceramic at low cost. The internal electrode is formed of a metal having a silver content of 80 mass% or more, and the piezoelectric ceramic layer is formed of a piezoelectric ceramic containing silver and at least 1 alkaline earth metal element selected from calcium and barium, the alkaline earth metal element being contained in a total amount of 0.2 mol% or more and less than 2.0 mol% when the content of the element in the B site of the alkali metal niobate is 100 mol%, the piezoelectric ceramic layer containing at least 1 sintered particle (41) including a silver segregation region (42), and the silver segregation region (42) having a long diameter of 10nm or less.)

1. A laminated piezoelectric element, characterized in that:

has piezoelectric ceramic layers and internal electrodes,

the piezoelectric ceramic layer is composed of a piezoelectric ceramic containing an alkali metal niobate having a perovskite structure as a main component and containing at least 1 alkaline earth metal element selected from calcium and barium and silver,

wherein the total content of the alkaline earth metal elements is 0.2 mol% or more and less than 2.0 mol% when the content of the element in the B site of the alkali metal niobate is 100 mol%,

the piezoelectric ceramic layer contains at least 1 sintered particle containing silver segregation region,

the long diameter of the silver segregation region is 10nm or less,

the internal electrodes are disposed between the piezoelectric ceramic layers, and are formed of a metal having a silver content of 80 mass% or more.

2. The laminated piezoelectric element according to claim 1, wherein:

the piezoelectric ceramic layer contains at least 1 sintered particle containing 5 or more silver segregation regions.

3. The laminated piezoelectric element according to claim 1 or 2, wherein:

the alkali metal niobate is represented by the following composition formula (1),

(Ag_tM2_u(K_1－v－wNa_vLi_w)_1－t－u)_a(Sb_xTa_yNb_{1－x－y－z}Zr_z)O₃…(1)

in the composition formula (1), M2 represents the alkaline earth metal element, and t, u, v, w, x, y, z, a are values of inequalities satisfying 0.005 < t < 0.05, 0.002 < u < 0.02, 0.007 < t + u < 0.07, 0 < v < 1, 0.02 < w < 0.1, 0.02 < v + w < 1, 0 < x < 0.1, 0 < y < 0.4, 0 < z < 0.02, and 1 < a < 1.1.

4. The multilayer piezoelectric element according to any one of claims 1 to 3, wherein:

the piezoelectric ceramic layer contains Li and Si in addition to the constituent elements of the alkali metal niobate, and when the alkali metal niobate is taken as 100 mol%, the Li content is 0.1 mol% or more and 3.0 mol% or less, and the Si content is 0.1 mol% or more and 3.0 mol% or less.

5. The multilayer piezoelectric element according to any one of claims 1 to 4, wherein:

li is precipitated in the piezoelectric ceramic layer₃NbO₄。

6. The laminated piezoelectric element according to claim 4 or 5, wherein:

at least 1 compound selected from alkali metal silicate compounds and alkali metal niobium silicate compounds is precipitated in the piezoelectric ceramic layer.

7. The multilayer piezoelectric element according to any one of claims 1 to 6, wherein:

the piezoelectric ceramic layer contains Mn in addition to the constituent elements of the alkali metal niobate, and the content of Mn is 2.0 mol% or less when the alkali metal niobate is 100 mol%.

8. The laminated piezoelectric element according to claim 7, wherein:

an oxide containing manganese is precipitated in the piezoelectric ceramic layer.

9. The multilayer piezoelectric element according to any one of claims 1 to 8, wherein:

the sintering grain size in the piezoelectric ceramic layer satisfies that D50 is more than or equal to 100nm and less than or equal to 800nm and (D90-D10)/D50 is less than or equal to 2.0.

10. The multilayer piezoelectric element according to any one of claims 1 to 9, wherein:

and a protective portion covering the internal electrode and/or the piezoelectric ceramic layer.

11. The multilayer piezoelectric element according to any one of claims 1 to 10, wherein:

the internal electrodes are electrically connected every 1 layer by 1 pair of external electrodes provided on the surface.

12. A method of manufacturing a laminated piezoelectric element, comprising:

a step of preparing a green sheet containing a powder of an alkali metal niobate having a perovskite structure and an organic binder, and containing at least 1 alkaline earth metal element selected from calcium and barium, the total content of the alkaline earth metal elements being 0.2 mol% or more and less than 2.0 mol% with the content of the element in the B site of the alkali metal niobate being 100 mol%;

disposing an internal electrode precursor containing a metal having a silver content of 80 mass% or more on the green sheet;

a step of stacking the green sheets on which the internal electrode precursors are arranged to produce a stacked body; and

firing the laminate to obtain a fired body having internal electrodes between the sintered body layers,

the sintered body layer contains the alkali metal niobate as a main component, contains silver and at least 1 alkaline earth metal element selected from calcium and barium, and contains at least 1 sintered particle including a silver segregation region having a major diameter of 10nm or less.

13. The method of manufacturing a laminated piezoelectric element according to claim 12, wherein:

the sintered alkali metal niobate layer is represented by the following composition formula (1),

(Ag_tM2_u(K_1－v－wNa_vLi_w)_1－t－u)_a(Sb_xTa_yNb_{1－x－y－z}Zr_z)O₃…(1)

14. The method of manufacturing a laminated piezoelectric element according to claim 12 or 13, wherein:

the green sheet contains no silver.

Technical Field

The present invention relates to a piezoelectric element and a method for manufacturing the same.

Background

A piezoelectric element is an electronic component having a structure in which a piezoelectric ceramic (piezoelectric ceramic) is sandwiched between a pair of electrodes. Here, piezoelectricity refers to a property capable of converting electrical energy and mechanical energy into each other.

The piezoelectric element can move another object or move itself by converting a voltage applied between a pair of electrodes into mechanical energy such as pressure or vibration by utilizing the properties of the piezoelectric ceramic. On the other hand, the piezoelectric element can convert mechanical energy such as vibration or pressure into electric energy, and the electric energy can be obtained as a voltage between the pair of electrodes.

When the voltage applied between the electrodes is converted into mechanical vibration, the piezoelectric element can generate vibration of a wide frequency. Specifically, there may be mentioned vibrations in a frequency band of about 1 to 100Hz, which is called low-frequency sound, a frequency band of about 20Hz to 20kHz, which is called ultrasonic sound, which is present in a normal living environment, a frequency band of about 20kHz to several GHz, which is called electromagnetic wave, which is perceived as sound by humans, and a frequency band of about several to several tens GHz, which is called electromagnetic wave. Therefore, the piezoelectric element can be used for a microphone, a vibration member, and the like. On the other hand, the piezoelectric element can generate a voltage in a corresponding wide frequency band by sensing the vibration in the various frequency bands as described above.

As a structure of a piezoelectric element, a structure in which a plurality of piezoelectric ceramic layers are stacked with internal electrodes interposed therebetween is known, in addition to a structure in which electrodes are formed only on the surface of a piezoelectric ceramic. In the multilayer piezoelectric element, for example, an actuator or the like can be used in order to obtain a large displacement in the stacking direction of the plurality of piezoelectric ceramic layers. A multilayer piezoelectric element is typically manufactured by firing piezoelectric ceramic layers and internal electrodes at the same time.

Lead zirconate titanate (Pb (Zr, Ti) O) is widely used as the piezoelectric ceramic constituting such a piezoelectric element₃PZT) and solid solutions thereof. Since the PZT-based piezoelectric ceramic has a high Curie temperature, it can be obtained even in a high-temperature environmentPiezoelectric elements can be used. Further, since the piezoelectric ceramic has a high electromechanical coupling coefficient, there is an advantage that a piezoelectric element capable of efficiently converting electric energy and mechanical energy can be obtained. Further, the piezoelectric ceramic can be fired at a temperature of less than 1000 ℃ by selecting an appropriate composition, and therefore, there is an advantage that the manufacturing cost of the piezoelectric element can be reduced. In particular, the multilayer piezoelectric element described above can use a low-melting-point material with a reduced content of expensive materials such as platinum and palladium in the internal electrodes that are fired simultaneously with the piezoelectric ceramic, and can produce a significant cost reduction effect.

However, it is considered as a problem that PZT-based piezoelectric ceramics contain lead as a harmful substance, and instead, a piezoelectric ceramic composition not containing lead is required.

Hitherto, as a piezoelectric ceramic containing no lead, a piezoelectric ceramic having alkali metal niobic acid ((Li, Na, K) NbO) has been reported₃) Bismuth sodium titanate ((Bi)_0.5Na_0.5)TiO₃BNT), bismuth layered compound, tungsten bronze, and the like. Among these, alkali niobate-based piezoelectric ceramics have drawn attention as piezoelectric ceramics replacing PZT-based piezoelectric ceramics because of their high curie point and large electromechanical coupling coefficient ratio (patent document 1).

In the alkali niobate-based piezoelectric ceramics, silver is added in addition to an alkali metal element and niobium as main components for the purpose of lowering the sintering temperature and improving the characteristics (patent documents 2 to 4).

For example, patent document 2 discloses adding Ag to an alkali metal niobate-based compound powder₂O, promotion of Li during firing₃NbO₄The firing temperature can be lowered to about 1000 ℃.

Patent document 3 discloses that a piezoelectric ceramic in which Ag is precipitated in the voids in a sintered body of an alkali metal-containing niobate-based perovskite composition is suitable for use at high temperatures.

Patent document 4 discloses that a piezoelectric element having both high reliability and good piezoelectric characteristics can be manufactured at low cost by incorporating an alkaline earth metal and silver into an alkali metal niobate-based piezoelectric ceramic.

Documents of the prior art

Patent document

Patent document 1: international publication No. 2007/094115

Patent document 2: international publication No. 2012/086449

Patent document 3: japanese patent laid-open publication No. 2016-175824

Patent document 4: japanese patent laid-open publication No. 2017-163055

Disclosure of Invention

Technical problem to be solved by the invention

With recent technological advances, further miniaturization and higher performance of piezoelectric elements are required. If the piezoelectric element is miniaturized, the volume of the piezoelectric ceramic in the element is inevitably reduced and the inter-electrode distance is narrowed, and therefore, there is a tendency that the piezoelectric characteristics and the electric resistance thereof are lowered. Therefore, it is difficult to maintain the displacement amount or electromotive force of the piezoelectric element and to maintain the insulation between the electrodes to ensure reliability.

In addition, in the multilayer piezoelectric element, a metal having a high Ag content is often used as the internal electrode. In this case, Ag may diffuse into the piezoelectric ceramic during firing, which may reduce the resistance of the piezoelectric ceramic, thereby impairing the reliability of the multilayer piezoelectric element.

In patent document 2, Li is used₃NbO₄Since the deposition of (2) lowers the firing temperature of the piezoelectric ceramic, it is considered that the amount of Ag diffusion from the internal electrodes can be suppressed when forming a laminated piezoelectric element. However, due to Li₃NbO₄Since the piezoelectric ceramic has conductivity, there is a concern that the resistance of the piezoelectric ceramic decreases due to the precipitation method.

Further, as in patent document 3, when Ag is segregated in the voids in the sintered body to suppress the diffusion of Ag in the internal electrode, the segregation of Ag occurs at the grain boundaries in the piezoelectric ceramic. In a multilayer piezoelectric element in which the distance between internal electrodes is 50 μm or less, segregation of Ag in grain boundaries is likely to cause electrical conduction between electrodes, and even if the size of segregation of Ag is about 0.1 μm, the defect rate may be increased.

In patent document 4, the grain size of the piezoelectric ceramic is finely controlled by the diffusion of Ag from the internal electrodes, and a multilayer piezoelectric element having excellent characteristics can be obtained until the content of Ag in the internal electrodes is about 70 mass%. However, in order to further reduce the cost, when the content of silver in the internal electrodes is 80 mass% or more, the internal electrodes become liquid phase during firing, and there is a case where a multilayer piezoelectric element cannot be obtained.

Accordingly, an object of the present invention is to provide a multilayer piezoelectric element using an alkali niobate-based piezoelectric ceramic at low cost.

Technical solution for solving technical problem

The present inventors have conducted various studies to solve the above-mentioned problems, and as a result, have found that the above-mentioned problems can be solved by using a piezoelectric ceramic containing silver and at least 1 selected from calcium and barium as an alkali niobate-based piezoelectric ceramic and causing Ag segregation in the piezoelectric ceramic not to occur in a grain boundary but to occur in a grain interior, and have completed the present invention.

That is, one embodiment of the present invention for solving the above-described problems is a laminated piezoelectric element, characterized in that: the piezoelectric ceramic layer is composed of a piezoelectric ceramic containing an alkali metal niobate having a perovskite structure as a main component and containing at least 1 alkaline earth metal element selected from calcium and barium and silver, wherein the total content of the alkaline earth metal elements is 0.2 mol% or more and less than 2.0 mol% when the content of the element in the B site of the alkali metal niobate is 100 mol%, the piezoelectric ceramic layer contains at least 1 sintered particle including a silver segregation region, the length of the silver segregation region is 10nm or less, and the internal electrodes are disposed between the piezoelectric ceramic layers and are formed of a metal having a silver content of 80 mass% or more.

Another embodiment of the present invention is a method for manufacturing a laminated piezoelectric element, including: a step of preparing a green sheet containing a powder of an alkali metal niobate having a perovskite structure and an organic binder, and containing at least 1 alkaline earth metal element selected from calcium and barium, the total content of the alkaline earth metal elements being 0.2 mol% or more and less than 2.0 mol% when the content of the element in the B site of the alkali metal niobate is 100 mol%; disposing an internal electrode precursor containing a metal having a silver content of 80 mass% or more on the green sheet; a step of laminating the green sheets on which the internal electrode precursors are arranged to produce a laminate; and firing the laminate to obtain a fired body having internal electrodes between sintered body layers, the sintered body layers containing the alkali metal niobate as a main component, at least 1 alkaline earth metal element selected from the group consisting of calcium and barium, and silver, and at least 1 sintered particle containing a silver segregation domain having a long diameter of 10nm or less.

ADVANTAGEOUS EFFECTS OF INVENTION

According to the present invention, a multilayer piezoelectric element using an alkali niobate-based piezoelectric ceramic can be provided at low cost.

Drawings

Fig. 1 is a sectional view showing a structure of a multilayer piezoelectric element according to an embodiment of the present invention.

Fig. 2 is a perspective view showing a unit cell model of the perovskite structure.

Fig. 3 is a schematic view of a Transmission Electron Microscope (TEM) image of the piezoelectric ceramic layers constituting the multilayer piezoelectric element according to the embodiment of the present invention.

Fig. 4 is an example of a spectrum obtained when a silver segregation region in a piezoelectric ceramic layer constituting a multilayer piezoelectric element according to an embodiment of the present invention is measured by an energy dispersive X-ray spectrometer (EDS).

Fig. 5 is an example of a spectrum obtained when the outside of the silver segregation region in the piezoelectric ceramic layer constituting the multilayer piezoelectric element according to the embodiment of the present invention is measured by an energy dispersive X-ray spectrometer (EDS).

Description of the symbols

100 laminated piezoelectric element

10 internal electrode

20 side margin part

30 cover part

40 piezoelectric ceramic layer

41 sintered pellet

42 silver segregation regions.

Detailed Description

Hereinafter, the configuration and operation and effects of the present invention will be described together with the technical idea with reference to the drawings. However, the mechanism of action includes presumption, and its correctness is not intended to limit the present invention. Among the components in the following embodiments, components that are not described in the embodiments showing the highest concept will be described as arbitrary components. Note that the description of a numerical range (the description of connecting 2 numerical values "to" means that the numerical values described as the lower limit and the upper limit are included.

[ laminated piezoelectric element ]

A multilayer piezoelectric element 100 according to an embodiment of the present invention (hereinafter, may be abbreviated as "first embodiment") has a structure in which internal electrodes 10 are arranged between piezoelectric ceramic layers 40, as shown in a cross-sectional view thereof schematically illustrated in fig. 1. The internal electrode 10 is made of a metal containing silver in an amount of 80 mass% or more. In addition, among the internal electrodes 10 shown in fig. 1, electrodes with the same letter ("a" or "b") refer to electrodes of the same polarity. The piezoelectric ceramic layer 40 is composed of a piezoelectric ceramic containing an alkali metal niobate having a perovskite structure as a main component and containing at least 1 alkaline earth metal element selected from calcium and barium and silver, wherein the total content of the alkaline earth metal elements is 0.2 mol% or more and less than 2.0 mol% when the content of the element in the B site of the alkali metal niobate is 100 mol%, the piezoelectric ceramic layer 40 contains at least 1 sintered particle including a silver segregation region, and the long diameter of the silver segregation region is 10nm or less.

The internal electrode 10 is formed of a metal having a silver content of 80 mass% or more. By setting the silver content to 80 mass% or more, the amount of expensive metals such as platinum and palladium can be reduced, and the production cost of the element can be suppressed. Further, since the proportion of silver having excellent conductivity is increased, the resistivity of the internal electrode 10 is reduced, and the electrical loss when used as a piezoelectric element is reduced. Examples of the metal having a silver content of 80 mass% or more include silver-palladium alloy and silver. The content of silver in the metal constituting the internal electrode 10 is preferably 85 mass% or more, and more preferably 90 mass% or more.

The content of silver in the metal constituting the internal electrode 10 can be confirmed by elemental analysis of the internal electrode 10 using various measuring instruments and calculating the mass ratio of silver to all the detected elements. Examples of the measuring instrument to be used include an Energy Dispersive X-ray spectrometer (EDS: Energy Dispersive X-ray spectrometer) or a Wavelength Dispersive X-ray spectrometer (WDS: Wavelength Dispersive X-ray spectrometer) mounted on a Scanning Electron Microscope (SEM: Scanning Electron Microscope) or a Transmission Electron Microscope (TEM: Transmission Electron Microscope), an Electron Probe microanalyzer (EPMA: Electron Probe Micro Analyzer), and a laser irradiation inductively coupled plasma mass spectrometer (LA-ICP-MS).

The piezoelectric ceramic layer 40 contains an alkali metal niobate as a main component, and contains at least 1 alkaline earth metal element selected from calcium and barium, and silver.

The alkali metal niobate as a main component is an oxide having a perovskite structure containing at least one alkali metal element selected from lithium, sodium, and potassium as a constituent element and further containing niobium. Here, the perovskite structure is a crystal structure having an a site located at the apex of the cell, an O site located at the face center of the cell, and a B site located in an octahedron having the O site as the apex, as shown in fig. 2. In the alkali metal niobate in this embodiment, an alkali metal ion is located at the a site, a niobium ion is located at the B site, and an oxide ion is located at the O site. Further, various ions other than the above ions may be contained at each site.

The piezoelectric ceramic layer 40 contains at least 1 alkaline earth metal element selected from calcium and barium, and thus can obtain high piezoelectric properties and electrical insulation properties, and can provide a piezoelectric element having excellent characteristics. From the viewpoint of enhancing these effects, at least a part of the alkaline earth metal element contained is preferably solid-dissolved in the a site in the perovskite structure in the alkali metal niobate as the main component. At this time, the alkali niobate having the alkaline earth metal element dissolved therein becomes a main component of the piezoelectric ceramic layer 40.

The total content of at least 1 alkaline earth metal element selected from calcium and barium in the piezoelectric ceramic layer 40 is 0.2 mol% or more and less than 2.0 mol% assuming that the content of the element in the B site of the alkali metal niobate is 100 mol%. When the total content is 0.2 mol% or more, the piezoelectric ceramic layer 40 becomes a dense piezoelectric ceramic layer having a small sintered particle size, and exhibits excellent piezoelectric characteristics. From the viewpoint of enhancing the effect of the action, the total content is preferably 0.3 mol% or more, and more preferably 0.5 mol% or more. On the other hand, when the total content is less than 2.0 mol%, the electrical insulation of the piezoelectric ceramic layer 40 can be improved, and the piezoelectric ceramic layer can be used under a high electric field and can increase the device life. From this viewpoint, the total content is preferably less than 1.0 mol%, and more preferably 0.8 mol% or less.

The content of the element in the B site of the alkali metal niobate and the content of the alkaline earth metal element are determined based on the measurement result of the element ratio in the method of confirming the composition formula described later.

The piezoelectric ceramic layer 40 may contain, as an alkaline earth metal element, strontium other than calcium and barium. However, it is preferable that the alkaline earth metal element other than calcium and barium is not substantially contained because it is difficult to obtain a dense ceramic even if it is contained in a relatively small amount. The term "substantially free" means not containing an amount exceeding an amount inevitably mixed in a production process, such as an amount contained as an impurity in a raw material or an amount mixed in when an intermediate product is processed.

The piezoelectric ceramic layer 40 contains silver. Thereby, excellent piezoelectric characteristics are exhibited. The silver in the piezoelectric ceramic layer 40 is mainly dissolved in the a site of the above-described alkali metal niobate having a perovskite structure, or forms a silver segregation region described later. When silver is dissolved in the a site of the alkali metal niobate, the dissolved alkali metal niobate becomes a main component of the piezoelectric ceramic layer 40.

The alkali metal niobate, which is the main component of the piezoelectric ceramic layer 40, is preferably niobate represented by the following composition formula (1) from the viewpoint of exhibiting excellent piezoelectric characteristics and obtaining a device having a long lifetime when used under a high electric field.

(Ag_tM2_u(K_1－v－wNa_vLi_w)_1－t－u)_a(Sb_xTa_yNb_{1－x－y－z}Zr_z)O₃…(1)

Wherein M2 in the formula represents the above alkaline earth metal element. T, u, v, w, x, y, z and a are values satisfying inequalities represented by 0.005 < t.ltoreq.0.05, 0.002 < u < 0.02, 0.007 < t + u < 0.07, 0 < v.ltoreq.1, 0.02 < w.ltoreq.0.1, 0.02 < v + w.ltoreq.1, 0 < x.ltoreq.0.1, 0 < y.ltoreq.0.4, 0 < z.ltoreq.0.02, and 1 < a.ltoreq.1, respectively.

Here, the piezoelectric ceramic layer 40 can be determined by the following method, using an alkali metal niobate represented by the above composition formula as a main component: the piezoelectric ceramic layer 40 exposed on the surface of the multilayer piezoelectric element 100 or the powder obtained by pulverizing the multilayer piezoelectric element 100 is confirmed by measuring a diffraction line pattern with an X-ray diffractometer (XRD) using Cu — K α rays, confirming that the ratio of the strongest diffraction line intensity in the diffraction patterns from other structures to the strongest diffraction line intensity in the patterns from the perovskite structure is 10% or less, and then measuring the ratio of each element contained in the piezoelectric ceramic layer 40 with a high-frequency inductively coupled plasma emission spectrometer (ICP), an ion chromatograph, or a fluorescent X-ray analyzer (XRF), and confirming that the measurement result is the ratio in the composition formula. The method of exposing the piezoelectric ceramic layers 40 exposed on the surface of the multilayer piezoelectric element 100 when XRD measurement is performed is not particularly limited, and a method of cutting or polishing the piezoelectric element can be used. Further, the pulverizing means for XRD measurement of the powder obtained by pulverizing the multilayer piezoelectric element 100 is not particularly limited, and a hand mill (mortar, pestle) or the like can be used. In addition, since peaks of the metal constituting the internal electrode 10 were also detected when XRD measurement was performed on the powder obtained by pulverizing the multilayer piezoelectric element 100, the above confirmation was performed while excluding them.

In the alkali metal niobate represented by the above composition formula (1), Zr has an effect of suppressing a decrease in electric resistance in the sintered particles. That is, in the alkali metal niobate, since the alkaline earth metal element M2 is replaced with an alkali metal at the a site of the perovskite structure and is solid-solved, a positive charge is in an excessive state, and oxygen defects (interstitial oxygen) are likely to occur in order to equalize the charge. The oxygen defects become a conductivity factor under high temperature conditions, and the resistance of the sintered particles is lowered. However, by dissolving Zr having a small amount of positive charge in the B site of the perovskite structure, the occurrence of oxygen defects can be suppressed, and the reduction in resistance can be suppressed. From the viewpoint of the action of Zr, the content thereof is preferably about the same as that of the alkaline earth metal element M2. When the amount of Zr is too small compared to M2, charge compensation is insufficient. Conversely, when the amount of Zr is too large compared to M2, oxygen defects are caused by insufficient positive charge, and the resistance is rather lowered.

The piezoelectric ceramic layer 40 contains at least 1 sintered particle including a silver segregation region having a major diameter of 10nm or less. This can improve the electrical insulation of the piezoelectric element. This is considered to be because silver having high conductivity is not present between sintered particles which are likely to serve as a conduction path of current at high voltage. When the long diameter of the silver segregation region exceeds 10nm, a conductive path is formed in the sintered particle, and the electrical insulation property may be lowered, or the proportion of a portion not exhibiting piezoelectricity may be increased, and the piezoelectric property may be lowered. The major axis is preferably 8nm or less, and more preferably 5nm or less, from the viewpoint of suppressing a decrease in piezoelectric characteristics.

For confirmation of presence or absence of silver segregation region and measurement of long diameter thereof, morphological observation by a Transmission Electron Microscope (TEM) and characteristic X-ray measurement by an energy dispersive X-ray spectrometer (EDS) were used in combination. The specific measurement procedure is described below.

First, a multilayer piezoelectric element is manufacturedThe element 100 is a thin sheet having a thickness of about 100nm including the piezoelectric ceramic layer 40, which is obtained by using an ion beam or the like. The obtained thin sheet was observed with a TEM. In this case, the major axis of the silver segregation region to be confirmed is 10nm or less, and therefore the diameter of the electron beam irradiated to the thin section is converged to 1nm or less. As a result of the observation, after a region of about 10nm or less that appears white (bright) than the other portions was observed in the sintered pellet forming the piezoelectric ceramic layer 40, EDS measurements were performed on the regions that appear darker (dark) in the region and outside the region. The measurement conditions at this time were determined so that the intensity of the detected K line (K-K line) of potassium was 300 counts or more. The EDS measurement of the outer region is performed at a position sufficiently distant from the region appearing white and the outer periphery of the sintered pellet. Then, based on the measurement results, the ratio (I) of the intensity of Ag-L line to the intensity of K-K line was calculated for each region_Ag－L/I_K－K). Then, I in the above-mentioned region_Ag－L/I_K－KWhen the value of (b) is 2 times or more the value in the outer region, it is determined that the region is a silver segregation region, and the maximum length of a line segment that can be formed in the region is defined as the major diameter of the silver segregation region. Further, a white portion appeared in the inside of the sintered particle was confirmed by the TEM observation described above, and as a result of EDS measurement, I of the portion_Ag－L/I_K－KThe value of (A) is 2 times or more the value in the outer region, but if the length of a line segment that can be formed inside the region is too small to determine, it is also determined that a silver segregation region having a major diameter of 10nm or less exists.

Fig. 3 shows an example of a schematic TEM image of the piezoelectric ceramic layer 40 observed in this step. Fig. 4 shows an example of the EDS measurement results of a portion determined as a silver segregation region, and fig. 5 shows an example of the EDS measurement results of a portion determined as an outer side of the silver segregation region. Fig. 3 shows a state in which the sintered grains 41 include the silver segregation regions 42. In fig. 3, the silver segregation regions 42 are depicted in black, but in the actual TEM image, the silver segregation regions 42 appear white (bright) than the surroundings, as described above.

The piezoelectric ceramic layer 40 preferably contains at least 1 sintered particle including the silver segregation region 5 having the major axis of 10nm or less. This can exhibit more excellent piezoelectric characteristics. The number of silver segregation regions having a major diameter of 10nm or less in the sintered particle is more preferably 8 or more, and still more preferably 10 or more. The preferred number of silver segregation regions is only applied to the first embodiment in which the content ratio of silver in the metal constituting the internal electrode 10 is 80 mass% or more. In the multilayer piezoelectric element having the ratio of less than 80 mass%, the piezoelectric characteristics are rather degraded as the number of silver segregation regions in the sintered pellet increases.

The piezoelectric ceramic layer 40 may contain 0.1 mol% to 3.0 mol% of Li and 0.1 mol% to 3.0 mol% of Si, based on 100 mol% of the main component. By containing two elements of Li and Si, the piezoelectric ceramic layer 40 can be densified. In addition, the remaining Li that is not completely dissolved in the perovskite structure reacts with Si to produce Li₂SiO₃、Li₄SiO₄Compounds having high electric insulating property, inhibiting Li₃NbO₄The generation of a typical compound having conductivity contributes to suppressing a decrease in the resistivity of the piezoelectric ceramic layer 40. From the viewpoint of improving the effect, the molar ratio of Si to Li (Si/Li) is preferably 1.0 or more, and more preferably 2.0 or more.

From the viewpoint of sufficiently exhibiting the above-described functions, the content of Li is more preferably 0.3 mol% or more, and still more preferably 0.5 mol% or more with respect to 100 mol of the main component. On the other hand, by setting the content of Li to 3.0 mol% or less based on 100 mol% of the main component, it is possible to suppress Li from being contained₃NbO₄The piezoelectric ceramic is excellent in electrical insulation and durability due to the formation of a typical compound having electrical conductivity. From this point of view, the Li content is more preferably 2.0 mol% or less, and still more preferably 1.5 mol% or less, based on 100 mol% of the main component.

Li is also a constituent element of the main component described above, and the amount of Li described here does not include Li in the main component. The amount of Li not constituting the main component contained in the piezoelectric ceramic layer 40 can be calculated as the remaining amount of Li that can be dissolved in the alkali metal niobate after removing the amount of Li from the total amount of Li obtained as a result of the composition analysis in the method for determining the composition formula of the alkali metal niobate described above, or can be calculated based on the composition and the content of a compound other than the main component detected in the method for confirming the existence form of lithium niobate, lithium silicate, and manganese compound described later.

From the viewpoint of sufficiently exhibiting the above-described functions, the content of Si is more preferably 0.5 mol% or more, and still more preferably 1.0 mol% or more, relative to 100 mol% of the main component. On the other hand, when the content of Si is 3.0 mol% or less based on 100 mol% of the main component, the amount of different phases having no piezoelectricity can be suppressed, and a piezoelectric ceramic having excellent piezoelectric characteristics can be formed. From this point of view, the content of Si is more preferably 2.5 mol% or less, and still more preferably 2.0 mol% or less, relative to 100 mol% of the main component.

The piezoelectric ceramic layer 40 may contain Mn of 2.0 mol% or less with respect to 100 mol% of the main component. This increases the electrical resistance of the piezoelectric ceramic layer 40. The lower limit of the Mn content is not particularly limited, and is preferably 0.2 mol% or more from the viewpoint of sufficiently exerting the above-described effects. On the other hand, by setting the Mn content to 2.0 mol% or less, high piezoelectric performance can be maintained. The Mn content is preferably 1.5 mol or less, and more preferably 1.0 mol or less.

The mechanism by which the piezoelectric ceramic layer 40 increases the resistance by containing Mn is considered as follows. First, Mn easily forms an oxide having a high electric resistance at the triple point between the sintered particles of the alkali metal niobate and/or in the vicinity of the internal electrode 10. It is presumed that the presence of such a high-resistance oxide increases the resistance of the piezoelectric ceramic layer 40. As such high-resistance oxides, MnO and Mn can be exemplified₃O₄And MnO₂Etc. manganese oxide, Li₂MnO₃、LiMnO₄、LiMn₂O₄And KMnO₄Etc. of alkali metal elements and manganese, MnSiO₃、Mn₂SiO₄And Mn₇SiO₁₂Etc. of silicon and manganese, and Li as a composite oxide thereof₂MnSiO₄And NaMnSi₂O₆And the like. Further, Mn is thought to play a role of suppressing the variation in the valence number of the B site and maintaining the neutrality of the charge by being solid-dissolved in the B site of the alkali metal niobate having the perovskite structure or being located between lattices. That is, as described above, when the alkaline earth metal element M2 is substituted with an alkali metal located at the a site of the perovskite structure for solid solution, the valence of Nb, Ta, Sb, or the like located at the B site varies depending on the valence of the alkali metal, and the resistance may be lowered. At this time, Ca (Mn) is generated by solid dissolution of Mn as a divalent cation in the B site_1/3Nb_2/3)O₃、Ba(Mn_1/3Nb_2/3)O₃And so on, thereby suppressing a decrease in resistance.

The existence form of the lithium niobate, lithium silicate, and manganese compound can be confirmed by measuring the distribution of Li, Mn, and Si in the piezoelectric ceramic layer 40. Examples of the measuring instrument for the distribution include an Energy Dispersive X-ray spectrometer (EDS: Energy Dispersive X-ray spectrometer) or a Wavelength Dispersive X-ray spectrometer (WDS: Wavelength Dispersive X-ray spectrometer), an Electron Probe microanalyzer (EPMA: Electron Probe Micro Analyzer), and a laser irradiation inductively coupled plasma mass spectrometer (LA-ICP-MS) mounted on a Scanning Electron Microscope (SEM: Scanning Electron Microscope) or a Transmission Electron Microscope (TEM: Transmission Electron Microscope).

The piezoelectric ceramic layer 40 may contain at least 1 kind selected from Sc, Ti, V, Cr, Fe, Co, Ni, Cu, and Zn as a first transition element as necessary. By containing these elements in an appropriate amount, the firing temperature of the multilayer piezoelectric element 100 can be adjusted, the grain growth can be controlled, and the life under a high electric field can be prolonged.

The piezoelectric ceramic layer 40 may contain at least 1 kind selected from Y, Mo, Ru, Rh, and Pd as a second transition element as necessary. By containing these elements in an appropriate amount, the firing temperature of the multilayer piezoelectric element 100 can be adjusted, the grain growth can be controlled, and the life under a high electric field can be prolonged.

The piezoelectric ceramic layer 40 may contain, as a third transition element, at least 1 selected from La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Re, Os, Ir, Pt, and Au, if necessary. By containing these elements in an appropriate amount, the firing temperature of the multilayer piezoelectric element 100 can be adjusted, the grain growth can be controlled, and the life under a high electric field can be prolonged.

Of course, in the first embodiment, a plurality of types of the first transition element, the second transition element, and the third transition element described above may be contained in the piezoelectric ceramic layer 40.

In the piezoelectric ceramic layer 40, it is preferable that the 10% diameter (D10), the 50% diameter (D50), and the 90% diameter (D90) in the particle size distribution expressed at the cumulative frequency of the sintered particles constituting the piezoelectric ceramic layer satisfy 100 nm. ltoreq. D50. ltoreq.800 nm and (D90-D10)/D50. ltoreq.2.0. By setting D50 to 100nm or more, the total area of the interfaces of the sintered particles can be reduced, and the piezoelectric properties can be prevented from being lowered due to the influence of the stress generated at the interfaces. From this point of view, D50 is more preferably 150nm or more, and still more preferably 200nm or more. On the other hand, a high resistance is exhibited by setting D50 to 800nm or less. From this point of view, D50 is more preferably 700nm or less, and still more preferably 600nm or less. Further, satisfying (D90-D10)/D50. ltoreq.2.0 further improves the resistance of the piezoelectric ceramic layer 40 and facilitates the thinning thereof.

Here, the particle size distribution of the sintered particles in the piezoelectric ceramic layer 40 is measured by the following procedure. First, platinum is vapor-deposited as a measurement sample on the piezoelectric ceramic layer 40 exposed on the surface of the piezoelectric element in order to impart conductivity. Next, the measurement sample was observed with a Scanning Electron Microscope (SEM), and a photograph of the sintered pellet was taken. Next, a plurality of mutually parallel straight lines are drawn in the photographed photograph, and the length of a line segment obtained by cutting each straight line by the peripheral edge of each sintered particle (the distance between 2 points at which each straight line intersects with the peripheral edge of the sintered particle) is defined as the particle diameter (particle size) of the sintered particle. The particle size of the sintered particles was measured for 400 or more particles by this method, and the number-based particle size distribution was determined from the obtained results. Finally, from the obtained particle size distributions, D10, D50 and D90 were calculated, respectively.

The method for exposing the piezoelectric ceramic layer 40 on the surface is not particularly limited, and a method of cutting or polishing the piezoelectric element can be used. When the piezoelectric ceramic layer 40 exposed in this way is removed from the surface of the piezoelectric ceramic so that the outline of the particles is not easily visible, heat treatment (thermal etching) may be performed for about 5 minutes at a temperature lower than the temperature at which the piezoelectric ceramic layer 40 is fired, before platinum deposition.

In the first embodiment, as shown in fig. 1, the side margin portion 20 may be formed between both side surfaces in the Y-axis direction and the internal electrode 10, or the cover portions 30 may be formed on the upper and lower surfaces in the Z-axis direction. The skirt portion 20 and the cap portion 30 function as a protective portion for protecting the piezoelectric ceramic layers 40 and the internal electrodes 10.

The skirt portion 20 and the cover portion 30 are preferably formed of an alkali metal niobate-based sintered body similar to the piezoelectric ceramic layer 40, from the viewpoints of shrinkage rate during firing of the multilayer piezoelectric element 100, relaxation of internal stress in the multilayer piezoelectric element 100, and the like. However, the material forming the side margin portion 20 and the cover portion 30 is not limited to the alkali niobate-based piezoelectric ceramic, as long as it is a material having high electrical insulation properties.

When the skirt portion 20 and the cover portion 30 are formed of the same alkali metal niobate-based sintered body as the piezoelectric ceramic layers 40, Ag contained in the internal electrodes 10 is preferably uniformly diffused as in the piezoelectric ceramic layers 40. This can ensure high electrical resistance in the skirt portion 20 and the cover portion 30 and suppress internal stress in the laminated piezoelectric element 100.

In the first embodiment, the first external electrode and the second external electrode (not shown) may be further provided on the surface of the multilayer piezoelectric element 100. At this time, the internal electrodes 10 are connected to different external electrodes for every 1 layer. According to this configuration, the electrical energy between the first external electrode and the second external electrode and the mechanical energy in the stacking direction of the piezoelectric ceramic layers 40 disposed between the internal electrodes 10 can be efficiently converted to each other.

The material constituting the external electrode is not particularly limited as long as it is a material having high conductivity and being physically and chemically stable under polarization conditions and under the use environment of the piezoelectric element. Examples of electrode materials that can be used include silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), and alloys thereof.

[ method for producing multilayer piezoelectric element ]

A method for manufacturing a multilayer piezoelectric element according to another embodiment of the present invention (hereinafter, may be abbreviated as "second embodiment") includes: a step of preparing a green sheet containing a powder of an alkali metal niobate having a perovskite structure and an organic binder, and containing at least 1 alkaline earth metal element selected from calcium and barium, the total content of the alkaline earth metal elements being 0.2 mol% or more and less than 2.0 mol% when the content of the element in the B site of the alkali metal niobate is 100 mol%; disposing an internal electrode precursor containing a metal having a silver content of 80 mass% or more on the green sheet; a step of laminating the green sheets on which the internal electrode precursors are arranged to produce a laminate; and firing the laminate to obtain a fired body having internal electrodes between sintered body layers, the sintered body layers containing the alkali metal niobate as a main component, at least 1 alkaline earth metal element selected from the group consisting of calcium and barium, and silver, and at least 1 sintered particle including a silver segregation region having a long diameter of 10nm or less.

The powder of the alkali metal niobate having a perovskite structure can be obtained, for example, by mixing a powder of a compound containing at least 1 alkali metal element selected from lithium, sodium, and potassium and a powder of a compound containing niobium in a desired ratio and firing (pre-firing) the mixture. In order to make the characteristics of the piezoelectric ceramic as a final product desired, a compound containing an alkali metal and an element other than niobium may be blended. When a commercially available alkali metal niobate powder can be used, it can be used as it is.

One example of the compound used is lithium carbonate (Li) as a lithium compound₂CO₃) Sodium carbonate (Na) as a sodium compound₂CO₃) And sodium bicarbonate (NaHCO)₃) Potassium carbonate (K) as a potassium compound₂CO₃) And potassium bicarbonate (KHCO)₃) And niobium pentoxide (Nb) as a niobium compound₂O₅). Further, as a compound which is an arbitrary component but is commonly used, tantalum pentoxide (Ta) as a tantalum compound is exemplified₂O₅) Antimony trioxide (Sb) as an antimony compound₂O₃) And the like.

The mixing ratio of the above-mentioned compounds is preferably adjusted so that the sintered body of the alkali metal niobate obtained by firing becomes a sintered body represented by the following composition formula (1).

(Ag_tM2_u(K_1－v－wNa_vLi_w)_1－t－u)_a(Sb_xTa_yNb_{1－x－y－z}Zr_z)O₃…(1)

By setting such a mixing ratio, when the element is integrally fired with an internal electrode made of a metal containing silver in an amount of 80 mass% or more, the element is excellent in piezoelectric characteristics and has a long service life even under a high electric field.

The method for mixing the compound powder is not particularly limited as long as the mixing of impurities is suppressed and the respective powders are uniformly mixed, and any of dry mixing and wet mixing may be employed. When wet mixing using ball milling is employed as the mixing method, for example, Partially Stabilized Zirconium (PSZ) beads are used, an organic solvent such as ethanol is used as a dispersion medium, the mixture is stirred by ball milling for about 8 to 60 hours, and then the organic solvent is evaporated and dried.

The conditions for the calcination of the obtained mixed powder are not particularly limited as long as the above-mentioned respective compound powders react to obtain the desired alkali metal niobate. For example, the firing is carried out in the air at a temperature of 700 to 1000 ℃ for 1 to 10 hours. The pre-fired powder can be directly supplied for the production of piezoelectric ceramics, and is preferably pulverized by a ball mill, a pounder or the like from the viewpoint of improving the mixing property with an alkaline earth metal compound and an organic binder described later.

In a second embodiment, a compound of at least 1 alkaline earth metal selected from calcium and barium is added to the above-described alkali metal niobate powder having a perovskite structure. As described later, the alkaline earth metal compound interacts with silver diffused from the internal electrode during firing to suppress the sintered particle size and the fluctuation thereof in the resulting sintered body, thereby forming a dense sintered body and contributing to the expression of excellent piezoelectric characteristics. As described later, the silver diffused from the internal electrode participates in the sintered grains to form a fine silver segregation region. From the viewpoint of improving these effects, it is preferable to make at least a part of the alkaline earth metal element solid-dissolve in the a site of the alkali metal niobate having the perovskite structure by adjusting the composition of the alkali metal niobate and the firing conditions.

The alkaline earth metal compound used is not particularly limited as long as it is a compound containing calcium or barium. These two elements may be contained in the compound, or other elements may be contained in the range where a desired piezoelectric ceramic can be obtained. As an example of the alkaline earth metal compound, calcium carbonate (CaCO) can be mentioned as the calcium-containing compound₃) Calcium metasilicate (CaSiO)₃) And calcium orthosilicates (Ca)₂SiO₄) The barium-containing compound may be barium carbonate (BaCO)₃)。

As the alkaline earth metal compound, a compound containing strontium or the like other than calcium and barium may be used. However, strontium and the like are preferably not substantially contained because of small interaction with Ag described later and, if the content thereof is large, it becomes difficult to obtain dense ceramics. Here, the term "substantially free" means not containing an amount that is inevitably mixed in the production process, such as an amount contained as an impurity in the raw material or an amount mixed in when the intermediate product is handled.

In the second embodiment, an organic binder is added to the above-described alkali metal niobate powder having a perovskite structure and the alkaline earth metal compound. The organic binder is not limited in its kind as long as it can mold and hold the mixture of the above-described components in a desired shape and volatilize carbon and the like without remaining by firing or a binder removal treatment before that. Examples of the organic binder that can be used include polyvinyl alcohol-based, polyvinyl butyral-based, cellulose-based, polyurethane-based, and vinyl acetate-based binders.

The amount of the organic binder used is not particularly limited, and is preferably as small as possible within a range that can achieve desired moldability and shape retention from the viewpoint of reducing the raw material cost because it is to be removed by a subsequent step.

The mixing method of the above components is not particularly limited as long as the components can be uniformly mixed while preventing the mixing of impurities. As an example, ball milling mixing may be mentioned.

When the above components are mixed, various additives such as a plasticizer for improving the moldability of the green sheet to be formed later and a dispersant for uniformly dispersing the powder may be mixed.

In addition, a compound or a composition which functions as a sintering aid may be mixed with an additive element for improving various properties of the piezoelectric ceramic, mainly Li, Si, and Mn described in the first embodiment. Examples of the compound used when the additive elements are mixed include lithium carbonate (Li) which is a compound containing Li₂CO₃) Silicon dioxide (SiO) as a compound containing Si₂) Manganese carbonate (MnCO) as a Mn-containing compound₃) Manganese monoxide (MnO) and manganese dioxide (MnO)₂) Manganese tetratrioxide (Mn)₃O₄) And manganese acetate (Mn (OCOCH)₃)₂) As a material containing Li and SiLithium orthosilicate (Li) of the compound of (1)₂SiO₃) And lithium orthosilicate (Li)₄SiO₄) And calcium metasilicate (CaSiO) as a compound containing Ca and Si₃) And calcium orthosilicates (Ca)₂SiO₄)。

Among these additive elements, Si reacts with an element contained in the alkali metal niobate or an element separately added during firing to precipitate Li₂SiO₃、Li₄SiO₄、K₃Nb₃O₆Si₂O₇、KNbSi₂O₇、K₃LiSiO₄Or KLi₃SiO₄And the like, or an amorphous phase containing these elements, whereby volatilization of the alkali metal and precipitation between the sintered particles can be suppressed, and is useful in this respect.

Further, Si also acts as a sintering aid by being used in combination with Li, and also has an effect of lowering the firing temperature. The amounts of Si and Li added at this time are preferably set within the ranges described in the first embodiment.

As described above, in the second embodiment, various additive elements can be mixed. However, if Ag is contained in the green sheet, it is preferable not to mix Ag in the second embodiment, which actively utilizes the diffusion of Ag, because the diffusion of Ag from the internal electrode to the sintered body layer during firing is suppressed.

As a method for molding a green sheet from the mixture of the above-mentioned components, a conventional method such as a doctor blade method or an extrusion molding method is used.

In the second embodiment, the internal electrode precursor containing a metal having a silver content of 80 mass% or more is disposed on the green sheet obtained in the above-described step. The internal electrode precursor may be disposed by a conventional method, and a method of printing or coating a paste containing a metal powder having a silver content of 80 mass% or more into the shape of the internal electrode is preferable from the viewpoint of cost. When the internal electrode precursor is disposed by printing or coating, the paste may contain a glass frit and/or a powder having the same composition as the alkali metal niobate powder contained in the green sheet in order to improve the adhesion strength to the sintered body layer after firing.

When the internal electrode precursors are disposed on the green sheets, the internal electrode precursors can be disposed so as to leave a space to be a side margin portion when forming the laminated piezoelectric element.

In the second embodiment, the green sheets on which the internal electrode precursors described above are arranged are stacked, and the green sheets are bonded to each other to produce a stacked body.

The lamination and bonding may be performed by a conventional method, and from the viewpoint of cost, a method of thermocompression bonding green sheets by the action of a binder is preferable.

In the lamination and pressure bonding, green sheets serving as cover portions in the case of forming the multilayer piezoelectric element may be added to both ends in the lamination direction. In this case, the additional green sheet may have the same composition as the green sheet on which the internal electrode precursor described above is disposed, or may have a different composition from the green sheet. From the viewpoint of making the shrinkage rate uniform during firing, the composition of the additional green sheet is preferably the same as or similar to that of the green sheet on which the internal electrode precursor is disposed.

In the second embodiment, the laminate obtained in the above-described step is fired. The organic binder may be removed from the stack prior to firing. In this case, the removal and firing of the organic binder may be continuously performed using the same firing apparatus. The conditions for removing the organic binder and firing may be appropriately set in consideration of the volatilization temperature and content of the binder, the sinterability of the piezoelectric ceramic composition, the durability of the internal electrode material, and the like. Examples of the conditions for removing the organic binder include a condition of performing the removal at a temperature of 300 to 500 ℃ for 1 to 5 hours in an atmospheric atmosphere. Examples of the firing conditions to be maintained include maintaining at 800 to 1100 ℃ for 1 to 5 hours in an atmospheric atmosphere. When a plurality of fired bodies for a multilayer piezoelectric element are obtained from 1 produced body (molded body), the produced body may be divided into a plurality of blocks before firing.

In the second embodiment, the above firing produces sintered layers of alkali metal niobate from the green sheets and internal electrodes from the internal electrode precursors, thereby obtaining a fired body having internal electrodes between the sintered layers containing alkali metal niobate as a main component. At this time, it is considered that Ag diffuses from the internal electrode to the sintered body layer, and it interacts with at least 1 alkaline earth metal element selected from calcium and barium. It is presumed that the sintered body layer becomes a dense sintered body layer formed of fine sintered particles by the interaction. It is also presumed that Ag which is not completely dissolved in the a site of the perovskite structure among Ag diffused in the sintered body layer suppresses the decrease in the electrical insulation of the sintered body layer by forming silver segregation regions having a major diameter of 10nm or less in the sintered particles. That is, when the content of Ag in the internal electrode is small and the amount of diffusion of Ag into the sintered body layer is small, Ag is dissolved in the a site of the alkali metal niobate having the perovskite structure in a solid state, and therefore the problem of the decrease in the electrical insulation property of the sintered body layer is not caused. However, if the content of Ag in the metal constituting the internal electrode is as high as 80 mass% or more, the amount of Ag diffused into the sintered body layer also increases, and Ag is produced in which the Ag is not completely dissolved in the A site. Conventionally, such Ag precipitates between sintered particles to form a conductive path, and thus the electrical insulation of the sintered body layer is lowered. However, in the second embodiment, the fine silver segregation regions are formed inside the sintered particles by the interaction between the specific alkaline earth metal element and Ag, and the decrease in the electrical insulation property can be suppressed.

In the second embodiment, a fired body obtained by firing is subjected to polarization treatment to produce a multilayer piezoelectric element. The polarization treatment is typically performed by forming a pair of electrodes on the surface of the fired body from a conductive material and applying a high voltage between the electrodes.

In forming the electrode, a conventional method such as a method of applying or printing a paste containing an electrode material to the surface of the sintered body and baking the paste, a method of depositing an electrode material on the surface of the sintered body, or the like can be used. As the electrode material, silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni), an alloy thereof, and the like, which are listed as the materials constituting the external electrode in the first embodiment, can be used.

The conditions for the polarization treatment are not particularly limited as long as damage such as cracks does not occur in the fired body and the directions of spontaneous polarization in the respective sintered body layers are aligned. As an example, an electric field of 4kV/mm to 6kV/mm is applied at a temperature of 100 ℃ to 150 ℃.

Examples

The present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(example 1)

[ production of multilayer piezoelectric element ]

As a powder of alkali metal niobate having a perovskite structure, a powder of composition formula Li was prepared_0.064Na_0.52K_0.42NbO₃The pre-fired powder shown. 0.5 mol% of BaCO was added to each of the calcined powders in an amount of 100 mol%₃0.65 mol% Li₂CO₃1.3 mol% SiO₂And 0.5 mol% of MnO and a polyvinyl butyral organic binder, and mixing them by wet ball milling. The resulting mixed slurry was shaped by blade coating to obtain a green sheet having a thickness of 80 μm. An Ag — Pd alloy paste (Ag/Pd mass ratio: 8/2) was screen-printed on the green sheets to form an electrode pattern, and the green sheets were stacked and pressed under a pressure of about 50MPa while being heated to obtain a laminate. After the laminate was singulated, the binder removal treatment was performed in the air, and then firing was performed at 1000 ℃ for 2 hours in the air to obtain a fired body. A conductive paste containing Ag was applied to the surface of the fired body, and was brought into contact with the internal electrodes exposed at every 1 layer on the surface, and the temperature was raised to 600 ℃. Finally, an electric field of 3.0kV/mm was applied between the pair of external electrodes in a constant temperature bath at 100 ℃ for 3 minutes to perform polarization treatment, thereby obtaining a multilayer piezoelectric element according to example 1.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

As a result of confirming the presence or absence of silver segregation regions in the sintered grains and measuring the length of the long diameter thereof, the silver segregation regions were confirmed in the sintered grains, and the long diameter lengths thereof were all 5nm or less. Further, it was confirmed that the sintered grains were included in the silver segregation region 5 having a major axis length of 5nm or less.

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

The piezoelectric ceramic layers in the obtained multilayer piezoelectric element were measured for the particle size distribution of the sintered pellets by the above-described method, and as a result, D50-550 nm, (D90-D10)/D50-1.15.

[ Electrical reliability test ]

The electrical reliability of the obtained multilayer piezoelectric element was evaluated by the average lifetime. The multilayer piezoelectric element was placed in a thermostatic bath at 100 ℃, a direct current field of 8kV/mm was applied between the external electrodes, and the time until the current value flowing between the external electrodes became 1mA or more was measured. And, the average value of this time for 10 elements was taken as the average lifetime. The average life time obtained was 1800 minutes.

[ evaluation of piezoelectric Properties ]

By piezoelectric constants d based on displacement₃₃The obtained multilayer piezoelectric element was evaluated for piezoelectric characteristics. The displacement amount of the multilayer piezoelectric element was measured by applying a unipolar sine wave having a maximum electric field of 8kV/mm to the element at about 100Hz, and using a laser doppler displacement meter. D is calculated from the measurement results₃₃Is 220 pm/V.

Comparative example 1

[ production of multilayer piezoelectric element ]

A multilayer piezoelectric element according to comparative example 1 was produced in the same manner as in example 1, except that the Ag — Pd alloy paste used for forming the electrode patterns on the green sheets was changed to an alloy paste having an Ag/Pd mass ratio of 7/3, and the firing temperature of the laminate was set to 950 ℃.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

The presence or absence of silver segregation regions in the sintered pellets and the length of the long diameter thereof were confirmed in the same manner as in example 1 for the piezoelectric ceramic layers in the obtained multilayer piezoelectric element, and as a result, silver segregation regions were confirmed in the sintered pellets, and the lengths of the long diameters thereof were all 10nm or less. However, the silver segregation regions observed include relatively large silver segregation regions having a major axis length of more than 5 nm. The number of silver segregation regions having a major-diameter length of 10nm or less, which are observed in the sintered pellet, is at most 3.

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

The piezoelectric ceramic layers in the obtained multilayer piezoelectric element were measured for the particle size distribution of the sintered pellets in the same manner as in example 1, and found that D50-450 nm, (D90-D10)/D50-0.95.

[ Electrical reliability test ]

The obtained multilayer piezoelectric element was evaluated for electrical reliability by the same method as in example 1, and as a result, the average lifetime was 3200 minutes.

[ evaluation of piezoelectric Properties ]

The piezoelectric characteristics of the obtained multilayer piezoelectric element were evaluated in the same manner as in example 1, and as a result, d ×₃₃Is 210 pm/V.

(example 2)

[ production of multilayer piezoelectric element ]

A multilayer piezoelectric element according to example 2 was produced in the same manner as in example 1, except that the Ag — Pd alloy paste used for forming the electrode patterns on the green sheets was changed to an alloy paste having an Ag/Pd mass ratio of 9/1, and the firing temperature of the laminate was 1030 ℃.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

As a result of confirming the presence or absence of silver segregation regions in the sintered pellets and measuring the length of the major axis of the silver segregation regions in the sintered pellets, the piezoelectric ceramic layers in the obtained multilayer piezoelectric element were confirmed in the same manner as in example 1, and as a result, silver segregation regions were confirmed in the sintered pellets, and the length of the major axis was 10nm or less, the length of the minimum major axis was 1.6nm, the length of the maximum major axis was 4nm, and the average major axis was 2.2 nm.

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

The grain size distribution of the sintered pellets of the piezoelectric ceramic layers of the multilayer piezoelectric element thus obtained was measured in the same manner as in example 1, and found that D50 was 680nm and (D90-D10)/D50 was 1.20.

[ Electrical reliability test ]

The obtained multilayer piezoelectric element was evaluated for electrical reliability by the same method as in example 1, and as a result, the average lifetime was 1200 minutes.

[ evaluation of piezoelectric Properties ]

The piezoelectric characteristics of the obtained multilayer piezoelectric element were evaluated in the same manner as in example 1, and as a result, d ×₃₃Is 225 pm/V.

(example 3)

[ production of multilayer piezoelectric element ]

Adding BaCO into the pre-sintered powder of alkali metal niobate₃Conversion to CaCO₃Otherwise, the multilayer piezoelectric element according to example 3 was produced in the same manner as in example 2.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

The presence or absence of silver segregation regions in the sintered pellets and the length of the long diameter thereof were confirmed in the same manner as in example 1 for the piezoelectric ceramic layers in the obtained multilayer piezoelectric element, and as a result, silver segregation regions were confirmed in the sintered pellets, and the lengths of the long diameters thereof were all 10nm or less. The major axes of the regions were confirmed to have a minimum major axis length of 1.5nm and a maximum major axis length of 4.5nm, and an average major axis length of 2.6 nm.

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

[ Electrical reliability test ]

The obtained multilayer piezoelectric element was evaluated for electrical reliability by the same method as in example 1, and the average lifetime was 1060 minutes.

[ evaluation of piezoelectric Properties ]

To and withThe piezoelectric characteristics of the obtained multilayer piezoelectric element were evaluated in the same manner as in example 1, and as a result, d ×₃₃Is 210 pm/V.

Comparative example 2

[ production of multilayer piezoelectric element ]

Adding BaCO into the pre-sintered powder of alkali metal niobate₃Change to SrCO₃A multilayer piezoelectric element according to comparative example 2 was produced in the same manner as in example 1, except that the Ag — Pd alloy paste used for forming the electrode patterns on the green sheets was changed to 7/3 alloy paste in terms of Ag/Pd mass ratio and the firing temperature of the laminate was set to 1100 ℃.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

The presence or absence of silver segregation regions in the sintered pellets and the length of the long diameter thereof were confirmed in the same manner as in example 1 for the piezoelectric ceramic layers in the obtained multilayer piezoelectric element, and as a result, silver segregation regions were confirmed in the sintered pellets, and the lengths of the long diameters thereof were all 10nm or less. The major axes of the regions were confirmed to have a minimum major axis length of 2.9nm and a maximum major axis length of 7.2nm, and the average major axis was 5.2 nm.

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

[ Electrical reliability test ]

The obtained multilayer piezoelectric element was evaluated for electrical reliability by the same method as in example 1, and as a result, the average lifetime was 1500 minutes.

[ evaluation of piezoelectric Properties ]

The piezoelectric characteristics of the obtained multilayer piezoelectric element were evaluated in the same manner as in example 1, and as a result, d ×₃₃Is 210 pm/V.

Comparative example 3

[ production of multilayer piezoelectric element ]

The production of the multilayer piezoelectric element according to comparative example 3 was attempted in the same manner as in comparative example 2, except that the Ag — Pd alloy paste used for forming the electrode patterns on the green sheets was changed to an alloy paste having an Ag/Pd mass ratio of 9/1, and the firing temperature of the laminate was 1030 ℃. However, a dense sintered body layer was not obtained in the obtained fired body.

Comparative example 4

[ production of multilayer piezoelectric element ]

The production of the multilayer piezoelectric element according to comparative example 4 was attempted in the same manner as in comparative example 3, except that the firing temperature of the laminate was 1100 ℃. However, the internal electrodes melt in the obtained fired body, and the laminated structure cannot be maintained.

The compositions of the internal electrodes and the sintered body layers of examples 1 to 3 and comparative examples 1 to 4 described above are shown in table 1, and the results of checking the firing temperature and the characteristics are shown in table 2.

[ Table 1]

[ Table 2]

From a comparison between examples 1 and 2 and comparative example 1, it was found that the multilayer piezoelectric element according to the example in which the piezoelectric ceramic layers are composed mainly of an alkali metal niobate, further contain calcium or barium, and further contain silver, and the internal electrodes are formed of a metal containing 80 mass% or more of silver exhibits excellent piezoelectric characteristics while retaining electrical insulation properties that can withstand practical use. Here, the very excellent electrical insulation (average life of the device) in comparative example 1 is understood to be due to the fact that the internal electrodes are formed of a metal having a low silver content and the amount of silver that diffuses into the piezoelectric ceramic layers during firing is small due to the low firing temperature. That is, when the internal electrodes are formed of a metal having a low silver content, the difference in silver concentration between the internal electrodes and the piezoelectric ceramic layers is small, and the driving force for diffusion of silver into the piezoelectric ceramic layers is small, and the amount of silver diffusion is reduced, whereby the sintering property of the piezoelectric ceramic layers is suppressed from being lowered due to the diffusion of silver. As a result, it can be said that the multilayer piezoelectric elements according to examples 1 and 2 can achieve improved piezoelectric characteristics while suppressing a decrease in electrical insulation properties, despite an increase in the amount of diffusion of silver into the piezoelectric ceramic layers.

Further, according to the comparison between examples 1 to 3 and comparative examples 2 to 4, it can be said that in the examples in which calcium or barium is added as an alkaline earth metal element to an alkali metal niobate, even when the internal electrode formed of a metal having a silver content of 80 mass% or more is integrally fired, a dense sintered body layer including fine silver segregation regions is formed in the sintered grains, and a multilayer piezoelectric element having excellent electrical reliability and piezoelectric properties can be obtained. On the other hand, it can be said that in the comparative example in which strontium was added as an alkaline earth metal element to an alkali metal niobate, when the internal electrode formed of a metal having a silver content of 70 mass% was fired integrally, a dense sintered body layer in which fine silver segregation regions were included in sintered particles was produced in the same manner as in the example, and a multilayer piezoelectric element having excellent electrical reliability and piezoelectric properties was obtained.

(examples 4 and 5)

[ production of multilayer piezoelectric element ]

Adding BaCO into the pre-sintered powder of alkali metal niobate₃A multilayer piezoelectric element according to example 4 was produced in the same manner as in example 2, except that the amount of (d) was changed to 0.2 mol% based on 100 mol% of the calcined powder and the firing temperature of the laminate was changed to 930 ℃. Further, the above BaCO is mixed with₃A multilayer piezoelectric element according to example 5 was produced in the same manner as in example 2, except that the amount of (d) was changed to 1.0 mol% based on 100 mol% of the above-mentioned pre-fired powder.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

As a result of confirming the presence or absence of silver segregation regions in the sintered grains and measuring the length of the major axis of the piezoelectric ceramic layer in each of the obtained laminated piezoelectric elements in the same manner as in example 1, silver segregation regions were confirmed in the sintered grains in any of the elements, and the length of the major axis was 10nm or less.

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

The piezoelectric ceramic layers in the obtained laminated piezoelectric elements were measured for the particle size distribution of the sintered particles in the same manner as in example 1, and as a result, in example 4, D50 ═ 2300nm, (D90-D10)/D50 ═ 2.40, and in example 5, D50 ═ 480nm, (D90-D10)/D50 were 0.90.

[ Electrical reliability test ]

The electrical reliability of each of the obtained laminated piezoelectric elements was evaluated in the same manner as in example 1, and the average lifetime was 500 minutes in example 4 and 50 minutes in example 5.

[ evaluation of piezoelectric Properties ]

The piezoelectric characteristics of each of the obtained laminated piezoelectric elements were evaluated in the same manner as in example 1, d ×₃₃195pm/V in example 4 and 210pm/V in example 5.

Comparative examples 5 and 6

[ production of multilayer piezoelectric element ]

Adding BaCO into the pre-sintered powder of alkali metal niobate₃The multilayer piezoelectric element according to comparative example 5 was fabricated in the same manner as in example 2, except that the amount of (d) was changed to 2.0 mol% based on 100 mol% of the calcined powder. However, a dense sintered body layer was not obtained in the obtained fired body. Therefore, the firing temperature was increased to 1100 ℃, and the production of the multilayer piezoelectric element according to comparative example 6 was attempted. However, the internal electrodes melt in the obtained fired body, and the laminated structure cannot be maintained.

(examples 6 and 7)

[ production of multilayer piezoelectric element ]

CaCO added into pre-sintered powder of alkali metal niobate₃A multilayer piezoelectric element according to example 6 was produced in the same manner as in example 3, except that the amount of (d) was changed to 0.2 mol% based on 100 mol% of the calcined powder and the firing temperature of the laminate was changed to 930 ℃. Alternatively, the above-mentioned CaCO₃A multilayer piezoelectric element according to example 7 was produced in the same manner as in example 3, except that the amount of (d) was changed to 1.0 mol% based on 100 mol% of the above-mentioned pre-fired powder.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

The piezoelectric ceramic layers in the obtained laminated piezoelectric elements were measured for the particle size distribution of the sintered particles in the same manner as in example 1, and as a result, D50-1200 nm, (D90-D10)/D50-2.60 in example 6, and D50-430 nm, (D90-D10)/D50-0.81 in example 7.

[ Electrical reliability test ]

The electrical reliability of each of the obtained laminated piezoelectric elements was evaluated in the same manner as in example 1, and the average lifetime was 400 minutes in example 6 and 10 minutes in example 7.

[ evaluation of piezoelectric Properties ]

The piezoelectric characteristics of each of the obtained laminated piezoelectric elements were evaluated in the same manner as in example 1, d ×₃₃170pm/V in example 6 and 220pm/V in example 7.

Comparative examples 7 and 8

[ production of multilayer piezoelectric element ]

CaCO added into pre-sintered powder of alkali metal niobate₃The multilayer piezoelectric element according to comparative example 7 was fabricated in the same manner as in example 3, except that the amount of (d) was changed to 2.0 mol% based on 100 mol% of the calcined powder. However, a dense sintered body layer was not obtained in the obtained fired body. Therefore, the firing temperature was increased to 1100 ℃, and the production of the multilayer piezoelectric element according to comparative example 8 was attempted. However, the internal electrodes melt in the obtained fired body, and the laminated structure cannot be maintained.

The compositions of the internal electrodes and the sintered body layers of examples 4 to 7 and comparative examples 5 to 8 described above are shown in Table 3, and the results of checking the firing temperature and the characteristics are shown in Table 4. Table 4 also shows the results of examples 2 and 3 described above in order to facilitate the understanding of the tendency of characteristic change due to the amount of the alkaline earth metal element added.

[ Table 3]

[ Table 4]

From the comparison of examples 2, 4 and 5 with comparative examples 5 and 6 and the comparison of examples 3, 6 and 7 with comparative examples 7 and 8, it can be said that when the laminated piezoelectric element is produced by adding less than 2.0 mol% of the alkaline earth metal element to 100 mol% of the element in the B site of the alkali metal niobate, a dense sintered body layer can be obtained without melting the internal electrode even when the internal electrode containing a metal having an Ag/Pd mass ratio of 9/1 is used, whereas when the amount of the alkaline earth metal element added is 2 mol% or more, it is difficult to obtain the laminated piezoelectric element having a dense sintered body layer without melting the internal electrode. In addition, from the comparison of examples 2, 4 and 5, and the comparison of examples 3, 6 and 7, it is presumed that: when the amount of the alkaline earth metal element added is in the range of 0.2 to 0.5 mol%, the electrical reliability and piezoelectric characteristics of the multilayer piezoelectric element are significantly improved and excellent piezoelectric characteristics are obtained when the amount of the alkaline earth metal element added is in the range of 0.5 to 1.0 mol% with an increase in the amount of the alkaline earth metal element added. The multilayer piezoelectric elements according to examples 5 and 7 have a short average life but excellent piezoelectric properties, and therefore can be suitably used in applications with a short lifetime.

(examples 8 to 11)

[ production of multilayer piezoelectric element ]

Adding ZrO to the presintering powder of alkali metal niobate₂A multilayer piezoelectric element according to example 8 was produced in the same manner as in example 5, except that the amount of (d) was changed to 0.2 mol% based on 100 mol% of the calcined powder, and the firing temperature of the laminate was changed to 1010 ℃. Further, the above-mentioned ZrO is subjected to₂A multilayer piezoelectric element according to example 9 was fabricated in the same manner as in example 5, except that the amount of (d) was changed to 0.5 mol% based on 100 mol% of the pre-fired powder, and the firing temperature was changed to 980 ℃. Further, the above-mentioned ZrO is subjected to₂A multilayer piezoelectric element according to example 10 was produced in the same manner as in example 8, except that the amount of (d) was changed to 1.0 mol% based on 100 mol% of the above-mentioned pre-fired powder. Further, the above-mentioned ZrO is subjected to₂A multilayer piezoelectric element according to example 11 was fabricated in the same manner as in example 5, except that the amount of (d) was changed to 2.0 mol% based on 100 mol% of the pre-fired powder, and the firing temperature was changed to 1020 ℃.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

The piezoelectric ceramic layers in the obtained laminated piezoelectric elements were measured for the particle size distribution of the sintered particles in the same manner as in example 1, and as a result, D50 ═ 550nm, (D90-D10)/D50 ═ 1.20 in example 8, D50 ═ 800nm, (D90-D10)/D50 ═ 1.34 in example 9, D50 ═ 1400nm, (D90-D10)/D50 ═ 2.1 in example 10, and D50 ═ 580nm, (D90-D10)/D50 ═ 1.12 in example 11.

[ Electrical reliability test ]

The electrical reliability of each of the obtained laminated piezoelectric elements was evaluated in the same manner as in example 1, and the average lifetime was 890 minutes in example 8, 1540 minutes in example 9, 200 minutes in example 10, and 100 minutes in example 11.

[ evaluation of piezoelectric Properties ]

The piezoelectric characteristics of each of the obtained laminated piezoelectric elements were evaluated in the same manner as in example 1, d ×₃₃220pm/V in example 8, 240pm/V in example 9, 235pm/V in example 10, and 210pm/V in example 11.

In examples 8 to 11 described above, the compositions of the internal electrodes and the sintered body layer are shown in Table 5, and the results of checking the firing temperature and the characteristics are shown in Table 6. Table 6 also shows the results of example 5 described above, in order to facilitate the understanding of the tendency of characteristic change due to the amount of Zr added.

[ Table 5]

[ Table 6]

From the comparison between examples 8 to 11 and example 5, it can be said that the multilayer piezoelectric element according to the embodiment of the present invention is manufactured by adding ZrO during the manufacturing process₂The piezoelectric ceramic layer contains Zr to improve electrical reliability. In addition, it can be said thatZrO added in calcined powder₂The piezoelectric properties are also improved up to about 1.0 mol%, that is, up to an amount approximately equal to at least 1 alkaline earth metal element selected from calcium and barium. These phenomena are presumed to be caused by introduction of Zr as a 4-valent cation into the B site, which is an oxygen defect that occurs when the amount of the alkaline earth metal element added is large⁴⁺Suppression is obtained.

(examples 12 to 15)

[ production of multilayer piezoelectric element ]

Respectively adding Li into the pre-sintered powder of alkali metal niobate₂CO₃And SiO₂A multilayer piezoelectric element according to example 12 was fabricated in the same manner as in example 2, except that the amounts of (a) and (b) were changed to 0.4 mol% and 0.8 mol% with respect to 100 mol% of the calcined powder, and the firing temperature of the laminate was changed to 940 ℃. Separately, the above Li is added₂CO₃And SiO₂A multilayer piezoelectric element according to example 13 was fabricated in the same manner as in example 2, except that the amounts of (a) and (b) were changed to 1.5 mol% and 3.0 mol% relative to 100 mol% of the pre-fired powder, and the firing temperature was changed to 930 ℃. Further, the above Li is added₂CO₃And SiO₂A multilayer piezoelectric element according to example 14 was produced in the same manner as in example 13, except that the amount of (d) was changed to 0.4 mol% and 2.0 mol% based on 100 mol% of the above-mentioned calcined powder. Further, the above Li is added₂CO₃And SiO₂A multilayer piezoelectric element according to example 15 was produced in the same manner as in example 2, except that the amounts of the components were changed to 1.5 mol% and 0.4 mol%, respectively, based on 100 mol% of the pre-fired powder, and the firing temperature was changed to 950 ℃.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

The piezoelectric ceramic layers in the obtained laminated piezoelectric elements were measured for the particle size distribution of the sintered particles in the same manner as in example 1, and as a result, D50 ═ 520nm, (D90-D10)/D50 ═ 0.85 in example 12, D50 ═ 480nm, (D90-D10)/D50 ═ 0.92 in example 13, D50 ═ 490nm, (D90-D10)/D50 ═ 1.20 in example 14, and D50 ═ 720nm, (D90-D10)/D50 ═ 1.60 in example 15.

[ Electrical reliability test ]

The electrical reliability of each of the obtained laminated piezoelectric elements was evaluated in the same manner as in example 1, and the average lifetime was 2200 minutes in example 12, 2150 minutes in example 13, 2600 minutes in example 14, and 280 minutes in example 15.

[ evaluation of piezoelectric Properties ]

The piezoelectric characteristics of each of the obtained laminated piezoelectric elements were evaluated in the same manner as in example 1, d ×₃₃195pm/V in example 12, 200pm/V in example 13, 180pm/V in example 14, and 210pm/V in example 15.

In examples 12 to 15 described above, the compositions of the internal electrodes and the sintered body layer are shown in Table 7, and the results of checking the firing temperature and the characteristics are shown in Table 8. Table 8 also shows the results of example 2 described above in order to facilitate the grasp of the tendency of characteristic changes due to the total amount of addition of Li and Si and the ratio thereof.

[ Table 7]

[ Table 8]

Based on the results obtained, it can be said that the present inventionIn the multilayer piezoelectric element according to one embodiment of the present invention, an appropriate amount of Li is added during production₂CO₃And SiO₂The firing temperature can be lowered. It is also presumed that the formation of a compound containing Li and Si and having high electrical insulation properties is supplemented with the miniaturization of sintered grains due to the lowering of the firing temperature, and the electrical insulation properties of the piezoelectric ceramic layers are improved, thereby obtaining a multilayer piezoelectric element having high electrical reliability. In particular, in example 14 in which the molar ratio Si/Li of Si to Li was larger than that in other examples, it is presumed that a multilayer piezoelectric element having particularly excellent electrical reliability was obtained by the formation of a compound rich in Si and having high electrical insulating properties.

In example 2, in order to reliably obtain a dense sintered body layer, firing was performed at a temperature close to the melting point of the internal electrode, but a laminate composed of green sheets not having the above composition did not form a dense sintered body layer by firing at a temperature lower than the firing temperature.

(examples 16 to 18)

[ production of multilayer piezoelectric element ]

A multilayer piezoelectric element according to example 16 was produced in the same manner as in example 2, except that the amount of MnO added to the alkali metal niobate pre-fired powder was changed to 0.2 mol% with respect to 100 mol% of the pre-fired powder, and the firing temperature of the laminate was changed to 1040 ℃. A multilayer piezoelectric element according to example 17 was produced in the same manner as in example 2, except that the amount of MnO was changed to 1.0 mol% based on 100 mol% of the pre-fired powder, and the firing temperature was changed to 1010 ℃. A multilayer piezoelectric element according to example 18 was produced in the same manner as in example 2, except that the amount of MnO was changed to 2.0 mol% based on 100 mol% of the pre-fired powder, and the firing temperature was changed to 990 ℃.

[ confirmation of silver segregation region in piezoelectric ceramic layer ]

[ measurement of particle size distribution of sintered particles in piezoelectric ceramic layer ]

The piezoelectric ceramic layers in the obtained laminated piezoelectric elements were measured for the particle size distribution of the sintered particles in the same manner as in example 1, and as a result, in example 16, D50 ═ 820nm, (D90-D10)/D50 ═ 1.40, in example 17, D50 ═ 510nm, (D90-D10)/D50 ═ 1.00, and in example 18, D50 ═ 450nm, (D90-D10)/D50 ═ 0.85.

[ Electrical reliability test ]

The obtained individual laminated piezoelectric elements were evaluated for electrical reliability by the same method as in example 1, and the average lifetime was 950 minutes in example 16, 1560 minutes in example 17, and 1610 minutes in example 18.

[ evaluation of piezoelectric Properties ]

The piezoelectric characteristics of each of the obtained laminated piezoelectric elements were evaluated in the same manner as in example 1, d ×₃₃220pm/V in example 16, 185pm/V in example 17 and 170pm/V in example 18.

In examples 16 to 18 described above, the compositions of the internal electrodes and the sintered body layer are shown in Table 9, and the firing temperatures and the results of checking the characteristics are shown in Table 10. Table 10 also shows the results of example 2 described above, in order to facilitate the understanding of the tendency of characteristic change due to the amount of Mn added.

[ Table 9]

[ Table 10]

From the obtained results, it can be said that the multilayer piezoelectric element according to one embodiment of the present invention can improve the electrical reliability by adding an appropriate amount of MnO at the time of manufacturing. This is presumably because Mn generates an oxide having high electrical resistance in the sintered body layer, and thereby increases the electrical resistance of the piezoelectric ceramic layer.

Industrial applicability of the invention

According to the present invention, a multilayer piezoelectric element using an alkali niobate-based piezoelectric ceramic 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 therefore can reduce the burden on the environment during its life cycle. Further, the multilayer piezoelectric element described above is also useful in that the resistivity is low because the content ratio of silver in the internal electrodes is high, and the electrical loss during use can be reduced. Further, according to a preferred embodiment of the present invention, a multilayer piezoelectric element having desired characteristics can be obtained by including various additive elements in the piezoelectric ceramic layer, and this is also useful in this respect.

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