Laminated piezoelectric ceramic element and device

Abstract

To provide an inexpensive and lead-free laminated piezoelectric ceramic element which has high insulation properties even if used for a long period of time at a high temperature in a high electric field, and a device using the same.SOLUTION: A laminated piezoelectric ceramic element 100 is obtained by alternately laminating internal electrodes 104 and 105 containing Ni as a main component and a piezoelectric ceramic layer 103 composed of a main phase containing an alkali niobate-based perovskite-type oxide and a sub-phase containing an oxide different from the alkali niobate-based perovskite-type oxide, wherein the alkali niobate-based perovskite-type oxide contains Ni, and the oxide of the sub-phase contains Mn and Ti.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a laminated piezoelectric ceramic element that is displaced by application of a voltage, and to a device using the same. [Background technology]

[0002] In recent years, attention has been focused on multilayer piezoelectric ceramic actuators, which are small and can be driven with high displacement even at low voltage.General multilayer piezoelectric ceramic elements contain PZT (lead zirconate titanate) piezoelectric ceramics, which contain lead, which has a negative impact on the environment, and expensive Pt or Pd in ​​the internal electrodes.

[0003] Therefore, there is a demand for low-cost multilayer piezoelectric ceramic components with low environmental impact.To address this, lead-free multilayer piezoelectric ceramics containing Ni, an inexpensive base metal, as the main component have been proposed (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5862983 [Patent Document 2] Patent No. 6094682 Summary of the Invention [Problem to be solved by the invention]

[0005] Actuators may be required to be used for long periods of time under high electric fields (for example, 5 kV / mm), so they must maintain high insulation properties even under such harsh conditions under high electric fields.

[0006] For example, Patent Documents 1 and 2 propose multilayer piezoelectric ceramic elements in which internal electrodes mainly composed of Ni and piezoelectric ceramic layers mainly composed of alkali niobate perovskite oxide are alternately stacked, but do not take into consideration durability under high electric fields.

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide an inexpensive, lead-free multilayer piezoelectric ceramic element that has high insulation properties even when used for a long period of time under a high electric field, and a device using the same. [Means for solving the problem]

[0008] (1) In order to achieve the above object, the multilayer piezoelectric ceramic element of the present invention employs the following measures: That is, the multilayer piezoelectric ceramic element of an application example of the present invention is a multilayer piezoelectric ceramic element in which internal electrodes containing Ni as a main component and piezoelectric ceramic layers each consisting of a main phase containing an alkali niobate perovskite oxide and a subphase containing an oxide different from the alkali niobate perovskite oxide are alternately stacked, wherein the alkali niobate perovskite oxide contains Ni and the oxide of the subphase contains Mn and Ti.

[0009] (2) In the multilayer piezoelectric ceramic element according to the application example of (1) above, the alkali niobate perovskite oxide contains 1.5 mol % or less of Ni.

[0010] (3) In the multilayer piezoelectric ceramic element according to the application example of (1) or (2) above, the alkali niobate perovskite oxide further contains at least one of Cu and Ag.

[0011] (4) In the multilayer piezoelectric ceramic element of (3) above, the alkali niobate perovskite oxide contains 0.5 mol % or less of Cu or Ag, respectively.

[0012] (5) Also, in any of the laminated piezoelectric ceramic elements of (1) to (4) above, the main component of the alkali niobate perovskite-type oxide has a composition formula (K 1-a-b Na a M b ) c (Nb 1-d-e-f Mn d Zr e Ti f )O 3+g (where element M is at least one of Ba, Ca, and Sr, 0 ≦ a ≦ 1.0, 0 ≦ b ≦ 1.0, 0 < a + b ≦ 1.0, c satisfies 0.8 ≦ c ≦ 1.2, 0 ≦ d ≦ 0.3, 0 ≦ e ≦ 0.3, 0 ≦ f ≦ 0.3, 0 ≦ d + e + f < 0.5, and g represents a value of oxygen deficiency or excess).

[0013] (6) Also, in any of the laminated piezoelectric ceramic elements of (1) to (5) above, the oxide of the secondary phase contains at least a Mn-Ti-O-based oxide.

[0014] (7) Also, the device of the application example of the present invention includes the laminated piezoelectric ceramic element described in any of (1) to (6) above.

[0015] (8) Also, the device of the application example of (7) above is selected from the group consisting of an actuator, haptics, a buzzer, and an ultrasonic sensor. [Advantages of the Invention]

[0016] According to the present invention, it is possible to obtain a laminated piezoelectric ceramic element or a device using the same that has high insulation even when used under a high electric field for a long time, is inexpensive, and is lead-free. [Brief Description of the Drawings]

[0017] [Figure 1] It is a front cross-sectional view of a laminated piezoelectric ceramic element. [Figure 2] It is a schematic diagram showing an example of the schematic configuration of an actuator as a device. [Figure 3] It is a cross-sectional view showing an example of the schematic configuration of haptics as a device. [Figure 4] FIG. 1 is a cross-sectional view showing an example of a schematic configuration of a buzzer as a device. [Figure 5] 1 is a cross-sectional view showing an example of a schematic configuration of an ultrasonic sensor as a device. [Figure 6] 1 is a table showing the composition and volume resistivity of the main phase of Samples 1-1 to 1-8. [Figure 7] 1 is a table showing the composition and volume resistivity of the main phase of Samples 2-1 to 2-9. [Figure 8] 1 is a table showing the composition and volume resistivity of the main phase of Samples 3-1 to 3-3. DETAILED DESCRIPTION OF THE INVENTION

[0018] Next, an embodiment of the present invention will be described with reference to the drawings. To facilitate understanding of the description, the same reference numerals are used to designate the same components in the drawings, and duplicated descriptions will be omitted.

[0019] [Embodiment] (Structure of multilayer piezoelectric ceramic element) 1 is a front cross-sectional view showing a multilayer piezoelectric ceramic element 100. In the multilayer piezoelectric ceramic element 100, piezoelectric ceramic layers 103 and internal electrodes 104, 105 are alternately stacked in the stacking direction, and expand and contract when a voltage is applied to the internal electrodes 104, 105. The piezoelectric ceramic layers 103 are polarized in alternating directions in the thickness direction.

[0020] The internal electrodes 104, 105 are taken out onto opposing side surfaces of the element and connected to external electrodes 106, 107, respectively, and different voltages can be applied from the external electrodes 106, 107 to adjacent internal electrodes 104, 105. Applying a voltage to the internal electrodes 104, 105 causes each piezoelectric ceramic layer 103 to expand and contract, causing the entire multilayer piezoelectric ceramic element 100 to expand and contract. Note that the multilayer piezoelectric ceramic element 100 shown in the reference diagram is just one example, and the present invention is not limited by the number and thickness of the piezoelectric ceramic layers 103, the shape of the multilayer piezoelectric ceramic element 100, etc.

[0021] The piezoelectric ceramic layer 103 is formed of a lead-free piezoelectric ceramic composition having a main phase containing an alkali niobate perovskite oxide and a subphase containing an oxide different from the alkali niobate perovskite oxide. The alkali niobate perovskite oxide contains Ni (nickel). The oxide of the subphase contains Mn (manganese) and Ti (titanium).

[0022] The electrode material used for the internal electrodes 104, 105 is a metal containing Ni (nickel) as its main component. "Containing Ni as its main component" means that the internal electrodes 104, 105 contain 50 vol% or more of Ni. The internal electrodes 104, 105 may contain Cu, Ag, or other metals. The electrode material used for the external electrodes 106, 107 is, for example, Au (gold), Ag (silver), Pd (palladium), Ni (nickel), Cu (copper), Pt (platinum), or an alloy thereof. The thickness of the internal electrodes 104, 105 is preferably 0.1 to 5 μm.

[0023] Thus, in the multilayer piezoelectric ceramic element 100 including internal electrodes 104, 105 formed of a metal containing Ni as a main component, and piezoelectric ceramic layer 103 having a main phase containing an alkali niobate perovskite oxide and a subphase containing an oxide different from the alkali niobate perovskite oxide, the alkali niobate perovskite oxide of the lead-free piezoelectric ceramic composition forming piezoelectric ceramic layer 103 contains Ni, and the oxide of the subphase contains Mn and Ti, thereby providing an inexpensive, lead-free multilayer piezoelectric ceramic element 100 that exhibits high insulation properties even after long-term use under a high electric field (e.g., 5 kV / mm, 100 hours). The thickness of each piezoelectric ceramic layer 103 is preferably 10 μm or more and 100 μm or less. The number of stacked piezoelectric ceramic layers 103 is preferably 2 to 200.

[0024] The main phase of the lead-free piezoelectric ceramic composition forming the piezoelectric ceramic layer 103 contains an alkali niobate perovskite oxide. The alkali niobate perovskite oxide has a perovskite structure. Metal oxides with a perovskite structure are generally represented by the composition formula ABO3 and are composed of a metal element located at the A site, a metal element located at the B site, and oxygen. In an ideal perovskite structure, 12 oxygen atoms are coordinated around the metal element at the A site, and 6 oxygen atoms are coordinated around the metal element at the B site, with this structure repeating periodically to form a crystal.

[0025] The alkali niobate perovskite oxide of the present invention preferably contains at least one alkali metal (potassium (K), sodium (Na), lithium (Li), etc.) as an alkaline component at the A site, and particularly preferably contains at least one of potassium (K) and sodium (Na). It also preferably contains niobium (Nb) at the B site. It may also contain an alkaline earth metal (at least one of calcium (Ca), strontium (Sr), barium (Ba), etc.) as an alkaline component at the A site. The effects of the present invention can also be achieved even if some of the alkaline component is located at the B site or niobium is located at the A site.

[0026] Furthermore, although the composition formula of a metal oxide having a perovskite structure is expressed as the composition formula ABO3 as described above, in reality, due to volatilization during firing and errors in composition analysis, the ratio of the amounts of the metal element in the A site, the metal element in the B site, and oxygen in the entire alkali niobate perovskite oxide may not necessarily be 1:1:3. Even in such cases, the piezoelectric ceramic layer 103 is within the scope of the present invention as long as it has a perovskite structure as its primary structure. Whether the piezoelectric ceramic layer 103 has a perovskite structure as its primary structure, i.e., whether the piezoelectric ceramic layer 103 contains a primary phase containing a perovskite oxide, can be determined, for example, from the results of X-ray diffraction (XRD) or transmission electron microscope (TEM) measurements of the piezoelectric ceramic layer 103. The fact that the piezoelectric ceramic layer 103 has a perovskite structure as its primary structure means that the characteristics of the perovskite structure are more pronounced than the characteristics of other crystal structures in the results of XRD or TEM measurements.

[0027] The content of Ni in the alkali niobate perovskite oxide is preferably 1.5 mol % or less, which further improves the insulating properties of the multilayer piezoelectric ceramic element 100.

[0028] The alkali niobate perovskite oxide preferably further contains at least one of Cu and Ag. In this case, the amount of Cu or Ag contained in the alkali niobate perovskite oxide is preferably 0.5 mol % or less, respectively. This further improves the insulating properties of the multilayer piezoelectric ceramic element 100.

[0029] The proportion of metal elements contained in the main phase crystal grains containing alkali niobate perovskite oxide was measured by qualitative and quantitative analysis using an electron probe microanalyzer (EPMA) on a polished cross section parallel to the stacking direction of the fired piezoelectric ceramic layer 103. Specifically, the main phase oxide crystal grains were first identified using a backscattered electron composition image at 5000x magnification taken with a scanning electron microscope (SEM) and a wavelength-dispersive x-ray spectroscopy (WDS) image taken with the EPMA in the same field of view. At least three main phase oxide crystal grains were then randomly selected from the resulting images. The crystal grains estimated to contain alkali niobate perovskite oxide based on the EPMA measurement results were then defined as main phase crystal grains. Next, qualitative and quantitative analysis was performed on the selected crystal grains using the EPMA, and the amount (molar number) of each metal element was calculated for each crystal grain. The average (arithmetic mean) is then calculated and used as the amount of the metal element contained in the alkali niobate perovskite oxide of the sample.The proportions (mol%) of the above metal elements can be calculated using the calculated amounts of all metal elements.

[0030] The proportion (mol %) of Ni, Cu, or Ag contained in an alkali niobate perovskite oxide is the proportion relative to the entire alkali niobate perovskite oxide, i.e., the proportion of Ni, Cu, or Ag contained in the crystal grains when the total proportion of all metal elements contained in the crystal grains having an alkali niobate perovskite oxide as the main crystal structure is taken as 100 mol %.

[0031] The cut surface of the piezoelectric ceramic layer 103 parallel to the stacking direction is positioned as far away as possible from the side of the multilayer piezoelectric ceramic element 100. The position of the piezoelectric ceramic layer 103 where the EPMA analysis is performed is near the center in the stacking direction and in the direction parallel to the stacking direction, and at approximately the same distance from the upper and lower internal electrodes 104, 105. This is because the piezoelectric ceramic layer 103 positioned close to the side of the multilayer piezoelectric ceramic element 100 may not be involved in the expansion and contraction of the multilayer piezoelectric ceramic element 100. The results of the EPMA analysis will be approximately the same if the piezoelectric ceramic layer 103 is sandwiched between the internal electrodes 104, 105.

[0032] The main component (components other than Ni, Ag, and Cu) of the alkali niobate perovskite oxide contained in the main phase is preferably a compound represented by the following composition formula (1).

[0033] (K 1-a-b Na a M b ) c (Nb 1-d-e-f Mn d Zr e Ti f )O 3+g ···(1)

[0034] In the above composition formula (1), the element M is at least one of alkaline earth metals Ba (barium), Ca (calcium), and Sr (strontium).

[0035] In the composition formula (1), theoretically, K (potassium), Na (sodium), and element M are arranged at the A site of the perovskite structure, and Nb (niobium), Mn (manganese), Zr (zirconium), and Ti (titanium) are arranged at the B site.

[0036] As the values ​​of the coefficients a to g in the composition formula (1), values ​​that are preferable in terms of the electrical properties (particularly insulating properties) or piezoelectric properties (particularly piezoelectric constant d33) of the lead-free piezoelectric ceramic composition are selected from among the combinations of values ​​that establish a perovskite structure.

[0037] Specifically, the coefficients a to f are 0≦a≦1.0 0≦b≦1.0 0 <a+b≦1.0 0.8≦c≦1.2 0≦d≦0.3 0≦e≦0.3 0≦f≦0.3 0≦d+e+f<0.5 It is preferable that the range is as follows. By doing so, it is believed that the piezoelectric properties and insulating properties can be further improved.

[0038] Furthermore, the coefficients a to f are further 0 <a<0.9 0 <b<0.3 0 <a+b<1.0 0.85≦c≦1.15 0 <d≦0.2 0 <e≦0.2 0 <f≦0.2 0 <d+e+f<0.5 It is preferable that the range is as follows. By doing so, it is believed that the piezoelectric properties and insulating properties can be further improved.

[0039] The oxygen coefficient (3+g) is usually 3, and the coefficient g is a positive or negative value indicating an oxygen deficiency or excess. The oxygen coefficient (3+g) can take any value that constitutes a perovskite oxide. A typical value for the coefficient g is g=0, and it is preferable that the coefficient g satisfies the condition -0.1≦g≦0.1. The value of the coefficient g can be calculated from the electrical neutrality condition of the main phase composition. However, compositions that slightly deviate from the electrical neutrality condition are also acceptable for alkali niobate perovskite oxide compositions.

[0040] The alkali niobate perovskite oxide according to this embodiment may contain other elements as needed, such as a composition containing at least one of Li, Ta, Sc, V, Cr, Fe, Co, Zn, Y, Mo, Ru, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, W, Re, Os, and Ir, for the purposes of improving piezoelectric properties and insulating properties, controlling the sintering temperature, and suppressing grain growth.

[0041] The metal oxide particles serving as the subphase component are preferably oxides of manganese and titanium (hereinafter referred to as Mn-Ti-O-based oxides). Mn-Ti-O-based oxides have a good affinity with the alkali niobate perovskite oxide serving as the main phase component, and can provide a highly reliable piezoelectric ceramic layer 103. Therefore, by incorporating Mn-Ti-O-based oxides as a subphase component into the piezoelectric ceramic layer 103 whose main component is alkali niobate perovskite oxide, a denser and more reliable piezoelectric ceramic layer 103 can be obtained.

[0042] The Mn—Ti—O-based oxide is represented by the following composition formula (2), for example.

[0043] MnTiO y ···(2) In the above composition formula (2), the coefficient y satisfies 2≦y≦8.

[0044] The Mn-Ti-O-based oxide preferably has a spinel structure or an inverse spinel structure, and examples of the Mn-Ti-O-based oxide include MnTiO and MnTiO, which can provide a more reliable piezoelectric ceramic layer 103.

[0045] Furthermore, the values ​​may deviate from the above-mentioned standard ranges as long as the structure can be maintained and the changes in the properties of the compound are within acceptable limits. For example, the Mn-Ti-O-based oxide may have a structure represented by the following composition formula (3) or (4).

[0046] Mn h Ti 2i O 4+j (3) Mn 2h Ti i O 4+j (4) In the above compositional formulas (3) and (4), the coefficients h and i are respectively 0.8 < h < 1.2 and 0.8 < i < 1.2, and the coefficient j is a positive or negative value indicating oxygen deficiency or excess.

[0047] In addition, the Mn-Ti-O-based oxide may contain other elements as necessary. For example, it is possible to contain elements such as Na, K, Zr, Ba, Ca, Sr, Ni, Cu, Ag, Sc, etc. The secondary phase may contain a plurality of types of Mn-Ti-O-based oxides. Further, the secondary phase may contain oxides other than the Mn-Ti-O-based oxide. For example, manganese oxides (MnOx oxides, such as MnO, MnO2, Mn3O4, etc.), manganese and niobium oxides (Mn-Nb-O-based oxides, such as Mn4Nb2O9, MnNb2O6, etc.) may be included.

[0048] The crystal structures of the crystal particles of the main phase and the secondary phase can be identified using XRD or TEM. The cut surface and the position of the piezoelectric ceramic layer 103 used for identifying the crystal structure of the crystal particles of the main phase or the secondary phase can be determined under the same conditions as the cut surface and the position of the piezoelectric ceramic layer 103 used for measuring the metal element ratio of the main phase. Also, when it can be inferred that the composition and its distribution of the crystal particles of the main phase and the secondary phase are generally the same even outside the above positions (for example, when the thicknesses of each piezoelectric ceramic layer 103 are almost the same), it may be identified using XRD or TEM for regions other than the cut surface and the position used for measuring the metal element ratio of the main phase, or it may be identified by performing powder XRD on the powder including the piezoelectric ceramic layer 103 of the sample.

[0049] In this embodiment, the proportion of the subphase contained in the lead-free piezoelectric ceramic composition is not particularly limited as long as it does not impair the object of the present invention. For example, it can be 0.1 vol% or more and 30 vol% or less. It is most preferable to determine the mixing ratio of the main phase and the subphase by measuring the porosity generated when firing the main phase alone in the firing profile to be implemented, and adding the subphase in a volume proportion that can fill the voids. In the case of the main phase composition in the examples described below, for example, 0.5 to 2.0 vol% is preferable.

[0050] (Device) The device 150 according to the embodiment of the present invention includes the multilayer piezoelectric ceramic element 100. The device 150 according to the embodiment of the present invention is preferably selected from the group consisting of, for example, an actuator 200, a haptic 300, a buzzer 400, and an ultrasonic sensor 500.

[0051] FIG. 2 is a schematic diagram illustrating an example of the overall configuration of an actuator 200 as the device 150. The actuator 200 is not particularly limited, and may be used, for example, in a valve opening / closing control unit of a mass flow controller or a stage driving unit of a precision positioning device to displace a driven body. The actuator 200 shown in FIG. 2 is composed of an actuator body 205, terminals 226 and 227, a seat 250, and a cap 260, and expands and contracts when a voltage is applied. When a voltage is applied to a pair of external electrodes 106 and 107 via a pair of lead wires 221 and 222, the actuator body 205 expands and contracts, causing the tip of the multilayer piezoelectric ceramic element 100 to displace. The terminals 226 and 227 are connected to the lead wires 221 and 222 of the actuator body 205 and transmit the applied voltage to the lead wires 221 and 222.

[0052] The actuator body 205 is composed of a multilayer piezoelectric ceramic element 100 and lead wires 221 and 222. The multiple multilayer piezoelectric ceramic elements 100 that make up the actuator body 205 are arranged and connected in series (multi-series), and their end faces are bonded together with an adhesive. Bonding multiple multilayer piezoelectric ceramic elements 100 together ensures a large displacement. Note that "series" refers to the expansion / contraction direction, i.e., the stacking direction D1 of the piezoelectric ceramic layers 103 and internal electrodes 104 and 105 within the multilayer piezoelectric ceramic element 100. The lead wires 221 and 222 connect terminals 226 and 227 to the external electrodes 106 and 107 of each multilayer piezoelectric ceramic element 100. The actuator body 205 may be formed from a single multilayer piezoelectric ceramic element 100 instead of multiple multilayer piezoelectric ceramic elements 100.

[0053] FIG. 3 is a cross-sectional view showing an example of a schematic configuration of a haptic 300 as device 150. Haptic 300 is not particularly limited, but may include, for example, a multilayer piezoelectric ceramic element 100 and a vibrating body in contact therewith. Haptic 300 shown in FIG. 3 is a device including a touch-sensitive display 310 and provides tactile feedback in response to an actuation signal. Touch-sensitive display 310 forms the upper surface of housing 320 and is in contact with display 330. Housing 320 contains multilayer piezoelectric ceramic element 100 bonded to substrate 340. Substrate 340 bends when multilayer piezoelectric ceramic element 100 contracts as a result of charge accumulation in multilayer piezoelectric ceramic element 100 or in response to an external force applied to touch-sensitive display 310.

[0054] FIG. 4 is a cross-sectional view showing an example of the schematic configuration of a buzzer 400 as the device 150. The buzzer 400 is not particularly limited, and may include, for example, a multilayer piezoelectric ceramic element 100 and a diaphragm in contact therewith. The buzzer 400 shown in FIG. 4 has a substantially disc-shaped exterior and includes a plastic case 410, a piezoelectric diaphragm 420 built into the case 410, and the multilayer piezoelectric ceramic element 100 in contact with the piezoelectric diaphragm 420. The case 410 is integrally formed with a cylindrical support ring 412 and a circular top plate 414 arranged to close an opening on one end of the support ring 412. A circular sound emission hole 430 is formed in the center of the top plate 414 and penetrates in the thickness direction. The piezoelectric diaphragm 420 is a plate material that is circular in plan view and is fitted and joined to the support ring 412 so as to close the opening on the other end. A resonance space 440 is formed inside the case 410 between the top plate 414 and the piezoelectric diaphragm 420. The resonance space 440 resonates in response to the vibration of the piezoelectric diaphragm 420. When a voltage is applied to the multilayer piezoelectric ceramic element 100, the piezoelectric diaphragm 420 vibrates, and sound waves generated from the piezoelectric diaphragm 420 are radiated to the outside through the sound emission holes 430.

[0055] 5 is a cross-sectional view showing an example of a schematic configuration of an ultrasonic sensor 500 as the device 150. The ultrasonic sensor 500 is not particularly limited, but may include, for example, a multilayer piezoelectric ceramic element 100 and a diaphragm in contact therewith. When a voltage is applied to the multilayer piezoelectric ceramic element 100, the diaphragm vibrates to emit ultrasonic waves, and the diaphragm receives the ultrasonic waves, causing the multilayer piezoelectric ceramic element 100 to output a voltage. The ultrasonic sensor 500 shown in FIG. 5 includes a bottomed cylindrical case 510 having an opening 512 at one axial end, the multilayer piezoelectric ceramic element 100 fixed to the inside bottom surface of the bottomed cylindrical case 510, an acoustic matching layer 520 fixed to the outside bottom surface of the bottomed cylindrical case 510 so as to face the multilayer piezoelectric ceramic element 100, a base member 530 closing the opening 512 of the bottomed cylindrical case 510, and a pair of input / output terminals 540, 550 fixed to the base member 530 and electrically connected to the multilayer piezoelectric ceramic element 100.

[0056] [Manufacturing method of multilayer piezoelectric ceramic element] An example of a method for manufacturing the multilayer piezoelectric ceramic element 100 will be described below.

[0057] (Method for producing calcined powder of main phase) First, necessary raw material powders of the main components of the alkali niobate perovskite oxide that will become the main phase are selected and weighed to achieve the desired composition. The raw material powders of the main components of the main phase may be oxides, carbonates, or hydroxides of the elements contained in the main phase. Ethanol is added to these raw material powders of the main phase, and the mixture is wet-mixed in a ball mill, preferably for 15 hours or more, to obtain a slurry. The resulting slurry is dried, and the resulting mixed powder is calcined, for example, in an air atmosphere at 600 to 1100°C for 1 to 10 hours, to obtain a calcined powder of the main components of the main phase.

[0058] Next, additives are selected as needed and weighed out to achieve a predetermined amount relative to the calcined powder of the main component of the main phase. The raw material powder of the additives may be oxides, carbonates, or hydroxides of the elements to be added as additives to the alkali niobate perovskite oxide that will form the main phase. Ethanol is then added to the powder obtained by mixing the additives with the calcined powder of the main component of the main phase, and the mixture is wet-mixed in a ball mill, preferably for 15 hours or more, to obtain a slurry. The slurry is dried, and the resulting mixed powder is then calcined, for example, in air at 600 to 1100°C for 1 to 10 hours to produce the calcined powder of the main phase.

[0059] In this way, calcined powder of the main phase can be produced. By producing calcined powder of the main components of the main phase and then adding additives, the piezoelectric properties of the main phase can be further improved. This is thought to be because segregation of the additives is less likely to occur. The additives of the main phase refer to Ni, Ag, and Cu. The main components of the main phase refer to components other than Ni, Ag, and Cu, such as K, Na, alkaline earth metal elements M, Nb, Mn, Zr, and Ti in composition formula (1). The calcined powder of the main phase may be produced by simultaneously mixing raw powders of the main components of the main phase and raw powders of the additives, without producing the calcined powder of the main components of the main phase.

[0060] (Method for producing calcined subphase powder) Separately from the above, necessary raw material powders of oxides that will become the subphase are selected and weighed to obtain the desired composition. The raw material powders of the subphase may be oxides, carbonates, or hydroxides of the elements contained in the subphase. For example, MnCO3, TiO2, etc. are selected as needed and weighed. Compounds of other metal elements may also be added. Ethanol is then added to these raw material powders of the subphase, and the mixture is wet-mixed in a ball mill, preferably for 15 hours or more, to obtain a slurry. The mixed powder obtained by drying the slurry is then calcined, for example, in an air atmosphere at 600 to 1300°C for 1 to 10 hours to produce a calcined powder of the subphase.

[0061] (Method for manufacturing multilayer piezoelectric ceramic elements) The calcined powders of the main component and the subphase prepared as described above are weighed out to a predetermined ratio, and a dispersant, binder, and organic solvent (e.g., toluene) are added. The mixture is then pulverized and mixed to obtain a slurry. The most suitable mixing ratio of the main phase and the subphase is determined by measuring the porosity generated when the main phase alone is fired using the firing profile to be implemented, and adding a volume fraction of the subphase that will fill the voids. The slurry is then processed into a sheet using a doctor blade method or other method to produce a ceramic green sheet. The film thickness of one layer of the laminate can be controlled by adjusting the thickness of the green sheet.

[0062] Next, an electrode layer that will become an internal electrode is formed on one surface of the ceramic green sheet by, for example, screen printing using a conductive paste for an internal electrode. The electrode layer is mainly composed of nickel (Ni).

[0063] Then, multiple ceramic green sheets with electrode layers formed thereon are stacked so that the electrode layers are exposed alternately from both sides, and ceramic green sheets without electrode layers are stacked on both the front and back sides of the resulting laminate. The resulting laminate is thermocompression bonded to obtain a laminate in which the ceramic green sheets and electrode layers are alternately stacked. This laminate is cut into a desired shape and then subjected to a binder removal treatment, for example, by holding it at a temperature of 200 to 400°C for 2 to 10 hours.

[0064] The laminate after the binder removal treatment is placed on an alumina setter, and heated at, for example, 1050°C and an oxygen partial pressure of 10 -12 The laminate is fired in a reducing atmosphere at 1000 kJ / cm² for 5 hours, then annealed in an N2 atmosphere at 800°C for 10 hours. Placing the laminate on an alumina setter for firing allows for stable production, and the N2 annealing process allows for the production of a highly insulating laminate.

[0065] After the annealing treatment, the side surfaces of the laminate are polished appropriately, and then a pair of external electrodes 106, 107 made of Au are formed on the side surfaces of the laminate by, for example, sputtering. The pair of external electrodes 106, 107 are formed facing each other with the laminate placed between them. The laminate with the external electrodes 106, 107 formed thereon is subjected to a polarization treatment to obtain a multilayer piezoelectric ceramic element 100. In this manner, a multilayer piezoelectric ceramic element 100 is obtained, which has a structure in which piezoelectric ceramic layers 103 made of a lead-free piezoelectric composition and internal electrodes 104, 105 mainly composed of Ni are alternately stacked.

[0066] The above-described manufacturing method is merely an example, and various other steps and processing conditions can be used to manufacture a multilayer piezoelectric ceramic element. For example, the firing conditions may be adjusted so that the Ni, Ag, or Cu compound diffuses from the electrode material during firing without being added to the main phase. Alternatively, instead of separately producing calcined products of the main phase and subphase and then mixing and firing the powders of both, the raw materials may be mixed in a quantitative ratio appropriate for the final composition of the lead-free piezoelectric composition and then fired. However, the method of separately producing calcined products of the main phase and subphase and then mixing them makes it easier to more strictly control the compositions of the main phase and subphase, thereby increasing the yield of the lead-free piezoelectric composition.

[0067] [Examples and Comparative Examples] (Samples 1-1 to 1-8) The composition of the main metal element of the main phase is (K 0.46 Na 0.47 Ba 0.07 )(Nb 0.87 Mn 0.03 Ti 0.03 Zr 0.07 K2CO3 powder, Na2CO3 powder, BaCO3 powder, Nb2O5 powder, MnCO3 powder, TiO2 powder, and ZrO2 powder were weighed as raw material powders for the main components of the main phase so that the composition satisfies the following formula: ethanol was added to these raw material powders for the main components of the main phase, and the mixture was wet-mixed in a ball mill for 15 hours or more to obtain a slurry. The slurry was then dried, and the resulting mixed powder was calcined in air at 930°C for 4 hours to produce a calcined powder of the main components of the main phase.

[0068] Next, for samples 1-2 to 1-8, NiO powder was weighed and added as the raw material powder of the main phase additive so that Ni was 0.015, 0.05, 0.15, 0.25, 0.5, 1.5, and 2.5 mol% relative to the total metal elements of the main phase, including the added Ni. Sample 1-1 did not contain NiO powder. The raw material powder of the additive was then added to the calcined powder of the main component of the main phase, and ethanol was added to the mixed raw material powder. The resulting mixture was wet-mixed in a ball mill for 15 hours or more to obtain a slurry. The resulting mixed powder with the additive added, which was dried, was then calcined at 930°C for 4 hours in an air atmosphere to produce the calcined powder of the main phase.

[0069] Separately, MnCO3 powder and TiO2 powder were weighed as raw material powders for the subphase so that the crystal structure of the subphase would be Mn2TiO4 oxide. Ethanol was added to these raw material powders for the subphase, and they were wet-mixed in a ball mill for more than 15 hours to obtain a slurry. The slurry was dried, and the resulting mixed powder was calcined in air at 1150°C for 5 hours to produce the calcined powder of the subphase.

[0070] Next, the calcined powders of the main phase and the subphase were weighed so that the ratio of the calcined powder of the subphase to the calcined powder of the main phase was 1.5 vol%. Next, a dispersant, a binder, and an organic solvent were added to the weighed calcined powders of the main phase and the subphase, and the mixture was pulverized and mixed to obtain a slurry. Next, the slurry was processed into a sheet shape using a doctor blade method to produce a ceramic green sheet. The thickness of the green sheet was adjusted so that the thickness of each piezoelectric ceramic layer of the multilayer piezoelectric ceramic element after firing would be approximately 75 μm. Next, a Ni-based electrode layer that would become the internal electrode was formed on one side of the ceramic green sheet by screen printing using a conductive paste for the internal electrode so that the thickness of the electrode after firing would be approximately 2 μm.

[0071] Then, multiple ceramic green sheets with electrode layers formed thereon were stacked so that the electrode layers were exposed alternately from both sides, and ceramic green sheets without electrode layers were further stacked on both the front and back sides of the resulting laminate. The number of ceramic green sheets sandwiched between the electrode layers was 11. The resulting laminate was thermocompression bonded to obtain a laminate in which ceramic green sheets and electrode layers were alternately stacked. This laminate was cut into the desired shape and then subjected to a binder removal treatment by holding it in a nitrogen atmosphere at 300°C for 5 hours.

[0072] The laminate after binder removal was placed on an alumina setter and heated at 1050°C with an oxygen partial pressure of 10 -12The laminate was then fired for 5 hours in a reducing atmosphere at 800°C. The laminate was then annealed for 10 hours in a N2 atmosphere at 800°C. The top, bottom, and side surfaces of the annealed laminate were then polished appropriately, and a pair of external electrodes made of Au were formed on the side surfaces of the laminate by sputtering. The laminate with the external electrodes was then placed in silicone oil at 40°C and subjected to a polarization treatment by applying a DC electric field of 3 kV / mm for 15 minutes, resulting in the production of multilayer piezoelectric ceramic elements (Samples 1-1 to 1-8). The dimensions of the multilayer piezoelectric ceramic element for each sample were approximately 8 mm in length, 8 mm in width, and 1 mm in height. Samples 1-1 to 1-8 are collectively referred to as Sample 1.

[0073] (Samples 2-1 to 2-9) The multilayer piezoelectric ceramic elements of Samples 2-1 to 2-9 were fabricated under the same conditions as the multilayer piezoelectric ceramic elements of Samples 1-1 to 1-8, except for the type and amount of additives. For Samples 2-1 to 2-9, NiO powder was weighed and added as the raw material powder of the main phase additive so that Ni accounted for 0.1 mol% of the total metal elements of the main phase, including the added Ni, Ag, and Cu. For Samples 2-1 to 2-4 and 2-9, AgO powder was weighed and added as the raw material powder of the main phase additive so that Ag accounted for 0.01, 0.05, 0.25, 0.5, and 0.05 mol%, respectively, of the total metal elements of the main phase. In addition, in samples 2-5 to 2-9, CuO powder was weighed and added as a raw material powder of an additive for the main phase so that Cu was 0.01, 0.05, 0.25, 0.5, and 0.05 mol%, respectively, relative to the total metal elements of the main phase. Samples 2-1 to 2-9 are collectively referred to as sample 2.

[0074] (Samples 3-1 to 3-3) The multilayer piezoelectric ceramic element of Sample 3-1 was fabricated under the same conditions as the multilayer piezoelectric ceramic element of Sample 1-1. The multilayer piezoelectric ceramic elements of Samples 3-2 and 3-3 were fabricated under the same conditions as the multilayer piezoelectric ceramic element of Sample 1-1, except that the oxygen partial pressure during firing was changed to the values ​​shown in the table of Fig. 8. Samples 3-1 to 3-3 are collectively referred to as Sample 3.

[0075] [Volume resistivity measurement] Each sample of multilayer piezoelectric ceramic element was placed in silicone oil at 50°C and subjected to a DC electric field of 5 kV / mm for 100 hours. After that, a DC electric field of 100 V / mm was applied at 25°C for 10 minutes, after which the insulation resistance was measured.

[0076] [Identification of the crystal structures of the main and subphases] The multilayer piezoelectric ceramic element of each sample was cut along a cross section passing through the center of the top surface and perpendicular to the stacking direction, and the main and subphases were identified by measuring XRD on the cut surface.

[0077] [Measurement of metal element ratio in the main phase] A position on the piezoelectric ceramic layer near the center of the same cut surface as above, roughly equidistant from the upper and lower internal electrode layers, was selected and quantitatively analyzed using an EPMA. First, a COMPO image at 5000x magnification was used with an SEM to identify the crystal grains of the alkali niobate perovskite oxide, the main phase. Next, a WDS image was taken with the same field of view, and three crystal grains of the main phase oxide were randomly selected from the image. Next, quantitative analysis was performed on the selected crystal grains using an EPMA, and the amount (number of moles) of each metal element was calculated for each crystal grain. The average (arithmetic mean) was then calculated and used as the amount of that metal element contained in the alkali niobate perovskite oxide of that sample. The calculated amounts of all metal elements were used to calculate the percentage of the metal elements (mol%).

[0078] [result] 6 to 8 are tables showing the composition and volume resistivity of the main phase of each sample. From the results of Sample 1, it was found that, with regard to the crystal structure of the main phase, by adding Ni to an alkali niobate-based perovskite-type oxide, the volume resistivity is improved and can be maintained even after the application of a high electric field. It was also found that a content of 1.5 mol% or less is preferable. The structure of the main phase identified for each sample was a perovskite-type oxide. The subphase identified was a spinel-type Mn2TiO4-based oxide.

[0079] The results of Sample 2 show that, with regard to the crystal structure of the main phase, by adding Ni to an alkali niobate perovskite oxide and further adding at least one of Ag and Cu, the volume resistivity is further improved and the volume resistivity can be maintained even after the application of a high electric field.

[0080] The results of Sample 3 show that adjusting the oxygen partial pressure during firing allows Ni to diffuse from the internal electrodes into the alkali niobate perovskite oxide main phase, improving the volume resistivity and allowing the volume resistivity to be maintained even after the application of a high electric field. It is presumed that Ag or Cu can also be adjusted by incorporating it into the internal electrodes and diffusing it during firing.

[0081] From the above results, it was confirmed that the multilayer piezoelectric ceramic element of the present invention is a multilayer piezoelectric ceramic element that has high insulating properties even when used for a long period of time under a high electric field.

[0082] The present invention is not limited to the above-described embodiments, and various modifications and equivalents are included within the spirit and scope of the present invention. Furthermore, the structure, shape, number, position, size, etc. of the components shown in each drawing are for the convenience of explanation and may be changed as appropriate. [Explanation of symbols]

[0083] 100 Multilayer piezoelectric ceramic element 103 Piezoelectric ceramic layer 104, 105 Internal electrode 106, 107 External electrode 150 equipment 200 Actuator 205 Actuator body 221, 222 lead wires Terminals 226 and 227 250 seats 260 Cap 300 Haptics 310 Touch-sensitive display 320 Housing 330 Display 340 PCB 400 Buzzer 410 cases 412 Support Ring 414 Top plate 420 Piezoelectric diaphragm 430 Sound emission hole 440 Resonance space 500 ultrasonic sensor 510 Cylindrical case with bottom 512 Opening 520 Acoustic matching layer 530 Base material 540, 550 input / output terminals D1 Stacking direction

Claims

1. A multilayer piezoelectric ceramic element in which internal electrodes containing Ni as a main component and piezoelectric ceramic layers each having a main phase containing an alkali niobate perovskite oxide and a subphase containing an oxide different from the alkali niobate perovskite oxide are alternately stacked, The alkali niobate perovskite oxide contains Ni, The laminated piezoelectric ceramic element is characterized in that the oxide of the subphase contains Mn and Ti.

2. 2. The multilayer piezoelectric ceramic element according to claim 1, wherein the alkali niobate perovskite oxide contains 1.5 mol % or less of Ni.

3. 3. The multilayer piezoelectric ceramic element according to claim 1, wherein the alkali niobate perovskite oxide further contains at least one of Cu and Ag.

4. 4. The multilayer piezoelectric ceramic element according to claim 3, wherein the content of Cu or Ag in the alkali niobate perovskite oxide is 0.5 mol % or less.

5. The main component of the alkali niobate perovskite oxide is represented by the composition formula (K １－ａ－ｂ Na ａ M ｂ ) ｃ (Nb １－ｄ－ｅ－ｆ Mn ｄ Zr ｅ Ti ｆ ) O ３＋ｇ 3. The multilayer piezoelectric ceramic element according to claim 1, wherein the element M is at least one of Ba, Ca, and Sr, 0≦a≦1.0, 0≦b≦1.0, 0<a+b≦1.0, c satisfies 0.8≦c≦1.2, 0≦d≦0.3, 0≦e≦0.3, 0≦f≦0.3, 0≦d+e+f<0.5, and g is a value indicating an oxygen deficiency or excess.

6. 3. The multilayer piezoelectric ceramic element according to claim 1, wherein the oxides in the subphase include at least an Mn--Ti--O-based oxide.

7. A device comprising the multilayer piezoelectric ceramic element according to claim 1 or 2.

8. 8. The device of claim 7, wherein the sensor is selected from the group consisting of an actuator, a haptic, a buzzer, and an ultrasonic sensor.

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