Lead-free piezoelectric ceramic composition, piezoelectric element, and device

Abstract

To provide a lead-free piezoelectric ceramic composition which has a high coupling coefficient, copes with a wide range of applied voltage, and has high output, and to provide a piezoelectric element and a device using them.SOLUTION: The lead-free piezoelectric ceramic composition contains at least a main phase of a perovskite-type oxide containing K, Na and Nb as main components, wherein the main phase contains domains divided by Σ = n symmetric tilt grain boundaries (n is an odd number of 5 or more). Thereby, the lead-free piezoelectric ceramic composition and the piezoelectric element having a high coupling coefficient, corresponding to a wide range of applied voltage, and having high output, and the device using them can be obtained.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a lead-free piezoelectric ceramic composition, a piezoelectric element, and an apparatus using the same.

Background Art

[0002] Conventionally, as a ceramic exhibiting piezoelectricity, PZT (lead zirconate titanate) has been widely used. However, since PZT contains lead in its components, its environmental impact has been regarded as a problem, and in recent years, the development of lead-free piezoelectric ceramic materials has been promoted. As one of the promising candidates for lead-free piezoelectric ceramic materials, there is a lead-free piezoelectric ceramic composition having a main phase composed of an alkali niobate-based perovskite oxide.

[0003] Patent Document 1 discloses a main phase containing an alkali niobate / tantalate-based perovskite oxide and a sub-phase containing a spinel compound containing Ti (titanium), containing Mn (manganese), the content ratio x of Ti being greater than 0 mol% and not more than 4 mol%, and the content ratio x of Ti and the content ratio y of Mn satisfying the following relational expression x 2 / y ≦ 20.0.

[0004] Patent Document 2 discloses a composition formula (A1 a M1 b ) c (Nb d1 , Mn d2 , M2 d3 )O 3+e (where element A1 is at least one of alkali metals, element M1 is at least one of Ba, Ca, Sr, element M2 is at least one of Ti, Zr, 0 < a < 1, 0 < b < 1, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 <1, 0 < d2 < 1, 0 < d3 < 1, d1 + d2 + d3 = 1, and e represents a value indicating oxygen deficiency or excess). A lead-free piezoelectric ceramic composition including a main phase composed of an alkali niobate-based perovskite oxide satisfying b / (d2 + d3)>  1.0 is disclosed.

Prior Art Documents

[0005] [Patent Document 1] International Publication No. 2022 / 215666 [Patent Document 2] International Publication No. 2023 / 026614 Summary of the Invention [Problem to be solved by the invention]

[0006] In order to obtain lead-free piezoelectric ceramics with properties equivalent to those of lead-containing piezoelectric ceramics, research and development has been carried out on domains, such as the introduction of fine domains and control of the amount of linear domain walls. However, it is known that it is difficult to obtain a high coupling coefficient with lead-free piezoelectric ceramic compositions whose main phase is an alkali niobate perovskite oxide through simple domain manipulation alone.

[0007] For example, Patent Documents 1 and 2 describe increasing the mechanical quality factor Qm of a lead-free piezoelectric ceramic composition having an alkali niobate perovskite oxide as the main phase, but do not consider improving the coupling coefficient of the lead-free piezoelectric ceramic composition having an alkali niobate perovskite oxide as the main phase.

[0008] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a lead-free piezoelectric ceramic composition, a piezoelectric element, and a device using the same, which have a high coupling coefficient, are compatible with a wide range of applied voltages, and have high output. [Means for solving the problem]

[0009] (1) In order to achieve the above object, the lead-free piezoelectric ceramic composition of the present invention employs the following means: That is, the lead-free piezoelectric ceramic composition of an application example of the present invention is a lead-free piezoelectric ceramic composition containing at least a main phase of a perovskite-type oxide containing K, Na, and Nb as main components, and the main phase contains domains separated by Σ=n symmetric tilt grain boundaries (n is an odd number of 5 or more).

[0010] (2) In the lead-free piezoelectric ceramic composition of the application example of (1) above, when the electron diffraction patterns of two domains on either side of the boundary of the Σ=n symmetric tilt grain boundary are indexed as a pseudo-cubic perovskite structure, the {210} diffraction spots of the two domains overlap each other.

[0011] (3) A piezoelectric element according to an application example of the present invention comprises a piezoelectric body made of the lead-free piezoelectric ceramic composition according to either (1) or (2) above, and electrodes in contact with the piezoelectric body.

[0012] (4) Furthermore, a device according to an application example of the present invention includes the piezoelectric element described in (3) above.

[0013] (5) Furthermore, the device of the application example of (4) above is selected from the group consisting of an actuator, a haptic, a buzzer, an ultrasonic sensor, an ultrasonic scalpel, an ultrasonic scaler, an ultrasonic cleaner, an ultrasonic processing machine, a piezoelectric transducer, and an ultrasonic motor. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a lead-free piezoelectric ceramic composition, a piezoelectric element, and a device using the same, which have a high coupling coefficient, are compatible with a wide range of applied voltages, and have high output. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a schematic diagram showing an example of a Σ=n symmetric tilt grain boundary. [Figure 2] Perovskite structure <100> 1 is a schematic diagram showing an example of a unit cell projected from the direction. [Figure 3] 1A and 1B are perspective views each showing an example of a piezoelectric element according to an embodiment of the present invention. [Figure 4] 1 is a schematic cross-sectional view showing an example of a multilayer piezoelectric element according to an embodiment of the present invention. [Figure 5] FIG. 1 is a schematic cross-sectional view showing an example of the schematic configuration of an actuator as a device. [Figure 6] FIG. 1 is a schematic cross-sectional view showing an example of the general configuration of a haptic device. [Figure 7] 1 is a schematic cross-sectional view showing an example of the general configuration of a buzzer as a device. [Figure 8] 1 is a schematic cross-sectional view showing an example of the schematic configuration of an ultrasonic sensor as a device. [Figure 9] FIG. 1 is a schematic diagram showing an example of a schematic configuration of an ultrasonic scalpel as a device. [Figure 10] 1 is a schematic diagram showing an example of the schematic configuration of an ultrasonic scaler as a device. [Figure 11] 1 is a schematic diagram showing an example of a schematic configuration of an ultrasonic cleaning device. [Figure 12] 1 is a schematic diagram showing an example of a schematic configuration of an ultrasonic processing machine as an apparatus. [Figure 13] 1 is a schematic diagram showing an example of a schematic configuration of a piezoelectric transducer as a device. [Figure 14] 1 is a schematic diagram showing an example of a schematic configuration of an ultrasonic motor as a device. [Figure 15] 1(a) and 1(b) are transmission electron microscope images of crystal particles of perovskite oxides containing K, Na, and Nb as main components, respectively, according to an example. [Figure 16] 1A and 1B are electron diffraction spot images of crystal grains containing Σ=n symmetric tilt grain boundaries of an example, and an explanation thereof, respectively. DETAILED DESCRIPTION OF THE INVENTION

[0016] 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.

[0017] [Embodiment] The lead-free piezoelectric ceramic composition of the present invention contains at least a main phase of a perovskite-type oxide containing K, Na, and Nb as its main components. The main phase also contains domains separated by Σ=n symmetric tilt grain boundaries (n is an odd number of 5 or more). This increases the bonding coefficient of the lead-free piezoelectric ceramic composition, allowing it to be used as a piezoelectric element with a wide range of applied voltages and high output.

[0018] A symmetric tilt grain boundary is a grain boundary in which two domains on either side of the grain boundary are joined with an offset of θ degrees, and the domains are arranged symmetrically, like a mirror image. The value of n is determined by the direction of the domain's rotation axis and the crystal plane (hkl) where the domains meet. Figure 1 is a schematic diagram showing an example of a Σ=n symmetric tilt grain boundary. In Figure 1, it can be seen that the upper and lower domains are arranged symmetrically, like a mirror image, with boundary L as the dividing line.

[0019] The reason for this effect is not yet fully understood, but the following mechanism is presumed. Specifically, the Σ=n symmetric tilt grain boundaries formed in the crystal grains of perovskite-type oxides primarily composed of K, Na, and Nb have a smaller angle than the rotation angle (approximately 90°) between domains that normally form, facilitating domain switching when voltage is applied. Therefore, it is presumed that the inclusion of domains separated by Σ=n symmetric tilt grain boundaries or crystal grains containing domains separated by Σ=n symmetric tilt grain boundaries in the main phase of a lead-free piezoelectric ceramic composition increases the coupling coefficient of the lead-free piezoelectric ceramic composition.

[0020] In the lead-free piezoelectric ceramic composition, when two domains sandwiching a boundary of a Σ=n symmetric tilt grain boundary in the main phase are indexed as a pseudo-cubic perovskite structure, the {210} diffraction spots preferably overlap each other in the electron diffraction pattern.Furthermore, the lead-free piezoelectric ceramic composition preferably contains domains separated by a Σ=5{210} symmetric tilt grain boundary in the crystal grains of the main phase.

[0021] Perovskite structures usually have multiple crystal systems, such as cubic, tetragonal, orthorhombic, and monoclinic. The lead-free piezoelectric ceramic composition of the present invention also has different crystal systems depending on the temperature. Figure 2 shows the crystal systems of the perovskite structure. <100> 2(a) shows an example of a unit cell projected from the direction. Figure 2(a) shows the simplest unit cell in a perovskite structure. Figure 2(b) shows a perovskite structure with a unit cell different from that in (1). The value of the index (such as

[0100] ) representing the direction varies depending on how the unit cell is chosen. Depending on the crystal system, a unit cell different from the simple unit cell shown in Figure 2(b) may be chosen, but in this specification, we will use indexes to refer to a pseudo-cubic perovskite structure.

[0022] The lead-free piezoelectric ceramic composition, the piezoelectric body 60 of the piezoelectric element 50 described below, or the piezoelectric layer 103 of the multilayer piezoelectric element 100 are prepared and observed using a transmission electron microscope as follows. First, the sample is polished using waterproof abrasive paper until the sample film thickness is approximately 50 μm. Next, a dimple grinder is used to grind the sample into a cone shape so that the sample film thickness at the center is approximately 20 μm. After that, an ion milling device is used to penetrate the sample near the center, cutting the sample into a wedge-shaped thin section.

[0023] The prepared samples are evaluated using a transmission electron microscope. High-resolution transmission electron microscope images are collected at 400,000 magnification of perovskite-type oxide crystal grains whose crystal orientation is adjusted to the

[0100] direction and whose main components are K, Na, and Nb. Electron diffraction images of the same grains are also collected with a camera length of 500 mm. The presence or absence of Σ=n symmetric tilt grain boundaries is determined by analyzing the atomic arrangement and diffraction spots from the high-resolution transmission electron microscope images and electron diffraction.

[0024] It is preferable that the cross section of the lead-free piezoelectric ceramic composition is perpendicular to the electrodes 71, 72 or the internal electrodes 104, 105 in the piezoelectric body 60 of the piezoelectric element 50 or the piezoelectric layer 103 of the multilayer piezoelectric element 100, at a position as far away from the side surface of the piezoelectric element 50 or the multilayer piezoelectric element 100 as possible. It is also preferable that the cross section is positioned approximately equidistant from the electrodes 71, 72 or the internal electrodes 104, 105. This is because the piezoelectric body 60 or the piezoelectric layer 103 positioned close to the side surface of the piezoelectric element 50 or the multilayer piezoelectric element 100 may not be involved in the expansion and contraction of the piezoelectric element 50 or the multilayer piezoelectric element 100. It is to be noted that the results of the above measurement in the multilayer piezoelectric element 100 will be approximately the same if the piezoelectric layer 103 is sandwiched between the internal electrodes 104, 105.

[0025] Perovskite oxides, whose main components are K, Na, and Nb, have 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.

[0026] The perovskite oxide of the present invention, which is mainly composed of K, Na, and Nb, contains potassium (K) and sodium (Na) as alkaline components at the A site, and may also contain other alkaline metals (lithium (Li), etc.). It also 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. Furthermore, the effects of the present invention can be obtained even if some of the alkaline components are located at the B site or niobium is located at the A site.

[0027] 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 A-site metal element, the B-site metal element, and oxygen in the entire perovskite oxide containing K, Na, and Nb as its main components may not necessarily be 1:1:3. Even in such cases, the lead-free piezoelectric ceramic composition is within the scope of the present invention as long as the main phase of the composition has a perovskite structure as its main structure. Whether the main phase of the lead-free piezoelectric ceramic composition has a perovskite structure as its main structure, i.e., whether the lead-free piezoelectric ceramic composition contains a perovskite oxide as its main phase, can be determined, for example, from the results of XRD or TEM measurement of a piezoelectric body 60 made of the lead-free piezoelectric ceramic composition in a piezoelectric element 50. The lead-free piezoelectric ceramic composition having a perovskite structure as its main 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.

[0028] The perovskite oxide of the main phase containing K, Na, and Nb as its main components is preferably a compound represented by the following composition formula (i).

[0029] (A1 a M1 b ) c (Nb d1 Mn d2 M2 d3 )O 3+e (i)

[0030] In the above composition formula (i), the element A1 includes at least alkali metals K (potassium) and Na (sodium), and may include Li (lithium). The element M1 is at least one of alkaline earth metals Ba (barium), Ca (calcium), and Sr (strontium). The element M2 is at least one of Ti (titanium) and Zr (zirconium).

[0031] As the values of the coefficients a to e in the compositional formula (1), among the combinations of values that form a perovskite structure, the electrical properties (especially insulation properties) or piezoelectric properties (especially piezoelectric constant d 33 ) of the lead-free piezoelectric ceramic composition are preferably selected.

[0032] Specifically, the coefficients a and b satisfy 0 < a < 1 and 0 < b < 1, and a = 0 (i.e., a composition containing no alkali metals) and b = 0 (i.e., a composition containing no Ba, Ca, or Sr) are excluded. Also, it is preferable that a + b = 1.

[0033] The coefficient c with respect to the entire A site satisfies 0.80 < c < 1.10, and 0.90 ≤ c ≤ 1.10 is preferable.

[0034] The coefficient d1 of Nb is preferably 0 < d1 < 1, more preferably 0.800 ≤ d1 ≤ 0.980. The coefficient d2 of Mn is preferably 0 ≤ d2 < 0.100, more preferably 0.001 ≤ d2 ≤ 0.080. The coefficient d3 of M2 is preferably 0 ≤ d3 < 0.400, more preferably 0.005 ≤ d3 ≤ 0.300. Also, it is preferable that d1 + d2 + d3 = 1. The perovskite-type oxide mainly composed of K, Na, and Nb can increase the mechanical quality factor Qm of the lead-free piezoelectric ceramic composition by containing Mn.

[0035] Among the coefficients 3 + e of oxygen, the coefficient e is a positive or negative value indicating oxygen deficiency or excess with respect to the coefficient of oxygen which is usually 3. The coefficient 3 + e of oxygen can take a value that constitutes an oxide with a perovskite structure as the main phase. A typical value of the coefficient e is e = 0, and 0 ≤ e ≤ 0.1 is preferable. The value of the coefficient e can be calculated from the electrical neutrality condition of the composition of the main phase. However, as the composition of the main phase, a composition slightly deviating from the electrical neutrality condition is also acceptable.

[0036] The oxide mainly composed of K, Na, and Nb represented by the above compositional formula (i) is referred to as "KNN" or "KNN material" and is excellent in piezoelectric properties, electrical properties, etc.

[0037] Incidentally, the above compositional formula (1) can be rewritten as the following compositional formula (iA).

[0038] (K a1 Na a2 Li a3 Ba b1 Ca b2 Sr b3 ) c (Nb d1 Mn d2 Ti d3 Zr d4 )O 3+e ···(iA)

[0039] The above compositional formula (1) and compositional formula (iA) are equivalent, where a1 + a2 + a3 = a and b1 + b2 + b3 = b. The coefficient a1 of K is 0 < a1 ≤ 0.7 (preferably, 0.095 ≤ a1 ≤ 0.665), the coefficient a2 of Na is 0 < a2 ≤ 0.9 (preferably, 0.285 ≤ a2 ≤ 0.855), and the coefficient a3 of Li is 0 ≤ a3 ≤ 0.2 (preferably, 0 ≤ a3 ≤ 0.1). Also, the coefficient b1 of Ba is 0 ≤ b1 ≤ 0.20, the coefficient b2 of Ca is 0 ≤ b2 ≤ 0.20, and the coefficient b3 of Sr is 0 ≤ b3 ≤ 0.20. The coefficient d3 of Ti is preferably 0 ≤ d3 < 0.100, more preferably 0.005 ≤ d3 ≤ 0.080. The coefficient d4 of Zr is preferably 0 ≤ d4 < 0.200, more preferably 0.005 ≤ d4 ≤ 0.150. Also, it is preferable that d1 + d2 + d3 + d4 = 1.

[0040] In addition, the perovskite-type oxide mainly composed of K, Na, and Nb according to this embodiment may contain other elements as necessary, and for the purposes of improving piezoelectric properties and insulation properties, controlling sintering temperature, suppressing crystal grain growth, etc., for example, a composition containing at least one of Sc, Ta, Ni, Cu, 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, Ir may be added.

[0041] The lead-free piezoelectric ceramic composition of the present invention may contain a subphase containing an oxide different from the main phase, in addition to a main phase of a perovskite-type oxide containing K, Na, and Nb as the main components. In this case, the subphase may be a tungsten bronze-type compound. This can improve the piezoelectric properties of the lead-free piezoelectric ceramic composition.

[0042] The tungsten bronze compound is a compound having a tungsten bronze structure represented by the following composition formula (ii).

[0043] C k D l O 15+δ (ii)

[0044] In the composition formula (ii), C contains one or more monovalent or divalent elements, and D contains one or more divalent to pentavalent elements. Furthermore, while k, l, and δ in the composition formula (ii) are typically k=3, l=5, and δ=0, respectively, they may deviate from the standard values ​​as long as they are within a range that allows the tungsten bronze structure to be maintained (without significant changes in properties), and impurity elements may also be included. Preferred ranges for k, l, and δ in the composition formula (ii) are, for example, 2.8≦k≦3.2, 4.8≦l≦5.2, and −1≦δ≦0.

[0045] A specific example of the composition represented by the composition formula (ii) is Ba3Nb5O 15 , Ba2KNb5O 15 , Ba2NaNb5O 15 The composition of the tungsten bronze-type compound that forms the subphase may deviate from the compositional ratio of the above composition formula (ii) or may contain some other elements. Furthermore, a spinel-type compound may be mixed as a subphase in addition to or instead of the subphase made of a tungsten bronze-type compound.

[0046] The subphase consisting of a tungsten bronze-type compound, when mixed with the main phase, facilitates polarization of the lead-free piezoelectric ceramic composition. It also suppresses deterioration of the piezoelectric properties, particularly the vibration properties, of the lead-free piezoelectric ceramic composition under high voltage. This is presumably because the inclusion of the subphase consisting of a tungsten bronze-type compound increases the hardness of the entire lead-free piezoelectric ceramic composition.

[0047] In the lead-free piezoelectric ceramic composition, the content of the subphase made of a tungsten bronze-type compound is preferably such that the ratio of the main peak of the subphase made of a tungsten bronze-type compound at around 13.2° (13.2°±0.1°) to the intensity of the main peak of the main phase made of an alkali niobate perovskite-type oxide is 100, is 0 to 4.2. The content of the subphase is more preferably 0.89 to 1.67, and even more preferably 1.5 to 1.67.

[0048] The presence of a subphase consisting of a tungsten bronze type compound in a lead-free piezoelectric ceramic composition can be confirmed by the presence of a peak different from that of the main phase at at least one of 13.2°±0.1°, 11.5°±0.1°, and 12.4°±0.1° in powder X-ray diffraction using X-rays with a wavelength of 0.7 Å.

[0049] The tungsten bronze type compound preferably exhibits a peak at 13.2°±0.1° in powder X-ray diffraction using X-rays with a wavelength of 0.7 Å, which makes it easy to confirm that the piezoelectric ceramic composition contains a subphase made of a tungsten bronze type compound.

[0050] The tungsten bronze type compound preferably contains Nb (niobium) and at least one of Ba (barium), Ca (calcium), Sr (strontium), Na (sodium), and K (potassium). This specifically constitutes the tungsten bronze type compound. The tungsten bronze type compound may also contain Mn.

[0051] (Structure of piezoelectric element) 3(a) and 3(b) are perspective views showing an example of a piezoelectric element 50 according to an embodiment of the present invention. FIG. 3(a) shows a disk-shaped piezoelectric element 50, and FIG. 3(b) shows a doughnut-shaped piezoelectric element 50 with a through hole. The piezoelectric element 50 includes a piezoelectric body 60 and electrodes 71 and 72 in contact with the piezoelectric body 60. The piezoelectric body 60 is made of the lead-free piezoelectric ceramic composition described above. One of the electrodes 71 and 72 is disposed on one side of the piezoelectric body 60, and the other is disposed on the other side of the piezoelectric body 60, with the piezoelectric body 60 sandwiched between the electrodes 71 and 72. Note that various other shapes and configurations can be adopted for the piezoelectric element 50.

[0052] (Structure of multilayer piezoelectric element) 4 is a cross-sectional view showing an example of a multilayer piezoelectric element 100 according to an embodiment of the present invention. The multilayer piezoelectric element 100 has piezoelectric layers 103 and internal electrodes 104, 105 alternately stacked in the stacking direction, and expands and contracts when a voltage is applied to the internal electrodes 104, 105. The piezoelectric layers 103 are polarized in alternating directions in the thickness direction.

[0053] The internal electrodes 104 and 105 are extended onto opposing side surfaces of the element and connected to external electrodes 106 and 107, respectively. Different voltages can be applied from the external electrodes 106 and 107 to adjacent internal electrodes 104 and 105. Applying a voltage to the internal electrodes 104 and 105 causes each piezoelectric layer 103 to expand and contract, causing the entire multilayer piezoelectric element 100 to expand and contract. The thickness of each piezoelectric layer 103 is preferably 10 μm or more and 100 μm or less. The number of stacked piezoelectric layers 103 is preferably 2 to 200. Note that the multilayer piezoelectric element 100 shown in the reference drawing is an example, and the present invention is not limited by the number and thickness of the piezoelectric layers 103, the shape of the multilayer piezoelectric element 100, etc.

[0054] The electrode material used for the electrodes 71, 72 or the internal electrodes 104, 105 is preferably a metal containing Ni (nickel) as its main component. "Containing Ni as its main component" means that Ni is contained in an amount of 50 vol% or more. The electrodes 71, 72 or 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 electrodes 71, 72 or the internal electrodes 104, 105 is preferably 0.1 to 5 μm.

[0055] (Device) The device 150 according to the embodiment of the present invention includes the above-described piezoelectric element 50 (including the multilayer piezoelectric 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 350, an ultrasonic sensor 400, an ultrasonic scalpel 450, an ultrasonic scaler 500, an ultrasonic cleaner 550, an ultrasonic processing machine 600, a piezoelectric transducer 650, and an ultrasonic motor 700.

[0056] FIG. 5 is a schematic diagram showing 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. 4 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 116 and 117 via a pair of lead wires 221 and 222, the piezoelectric actuator body 205 expands and contracts, causing the tip of the multilayer piezoelectric element 100 to be displaced. The terminals 226 and 227 are connected to the lead wires 221 and 222 of the piezoelectric actuator body 205 and transmit the applied voltage to the lead wires 221 and 222.

[0057] The piezoelectric actuator body 205 is composed of a multilayer piezoelectric element 100 and lead wires 221 and 222. The multiple multilayer piezoelectric elements 100 that make up the piezoelectric actuator body 205 are arranged and connected in series (multiplexed), and their end faces are bonded together with an adhesive. Bonding multiple multilayer piezoelectric elements 100 together ensures a large amount of displacement. Note that "series" refers to the expansion / contraction direction, i.e., the stacking direction D1 of the piezoelectric layers 103 and internal electrodes 104 and 105 within the multilayer piezoelectric element 100. The lead wires 221 and 222 connect terminals 226 and 227 to the external electrodes 106 and 107 of each multilayer piezoelectric element 100. The actuator body 205 may be formed from a single multilayer piezoelectric element 100 instead of multiple multilayer piezoelectric elements 100.

[0058] FIG. 6 is a cross-sectional view showing an example of a schematic configuration of a haptic 300 as device 150. Haptic 250 is not particularly limited, but may include, for example, a piezoelectric element 50 or a multilayer piezoelectric element 100 and a vibrator in contact therewith. The haptic 300 shown in FIG. 6 is a device including a touch-sensitive display 310 that provides tactile feedback in response to an actuation signal. The touch-sensitive display 310 forms the upper surface of a housing 320 and is in contact with a display 330. The housing 320 contains the piezoelectric element 50 or multilayer piezoelectric element 100 bonded to a substrate 340. The substrate 340 bends when the piezoelectric element 50 or multilayer piezoelectric element 100 contracts as a result of charge accumulation in the piezoelectric element 50 or multilayer piezoelectric element 100 or in response to an external force applied to the touch-sensitive display 310.

[0059] FIG. 7 is a cross-sectional view showing an example of the schematic configuration of a buzzer 350 as the device 150. The buzzer 350 is not particularly limited, and may include, for example, a piezoelectric element 50 or a multilayer piezoelectric element 100, and a diaphragm in contact therewith. The buzzer 350 shown in FIG. 7 has a substantially disc-shaped exterior shape and includes a plastic case 360, a piezoelectric diaphragm 370 built into the case 360, and the piezoelectric element 50 or the multilayer piezoelectric element 100 in contact with the piezoelectric diaphragm 370. The case 360 ​​is integrally formed with a cylindrical support ring 362 and a circular top plate 364 arranged to close an opening on one end of the support ring 362. A circular sound emission hole 380 is formed in the center of the top plate 364, penetrating in the thickness direction. The piezoelectric diaphragm 370 is a plate material that is circular in plan view, and is fitted and joined to the support ring 362 so as to close the opening on the other end. A resonance space 390 is formed inside the case 360 ​​between the top plate 364 and the piezoelectric diaphragm 370. The resonance space 390 resonates in response to the vibration of the piezoelectric diaphragm 370. When a voltage is applied to the piezoelectric element 50 or the multilayer piezoelectric element 100, the piezoelectric diaphragm 370 vibrates, and sound waves generated from the piezoelectric diaphragm 370 are radiated to the outside through the sound emission holes 380.

[0060] 8 is a cross-sectional view showing an example of a schematic configuration of an ultrasonic sensor 400 as the device 150. The ultrasonic sensor 400 is not particularly limited, but may, for example, include a piezoelectric element 50 or a multilayer piezoelectric element 100 and a diaphragm in contact therewith, and when a voltage is applied to the piezoelectric element 50 or the multilayer piezoelectric element 100, the diaphragm vibrates and emits ultrasonic waves, and when the diaphragm receives the ultrasonic waves, the piezoelectric element 50 or the multilayer piezoelectric element 100 outputs a voltage. The ultrasonic sensor 400 shown in FIG. 8 includes a bottomed cylindrical case 410 having an opening 412 at one axial end, a piezoelectric element 50 or a multilayer piezoelectric element 100 fixed to the inside of the bottom surface of the bottomed cylindrical case 410, an acoustic matching layer 420 fixed to the outside of the bottom surface of the bottomed cylindrical case 410 so as to face the piezoelectric element 50 or the multilayer piezoelectric element 100, a base member 430 that closes the opening 412 of the bottomed cylindrical case 410, and a pair of input / output terminals 441, 442 that are fixed to the base member 430 and electrically connected to the piezoelectric element 50 or the multilayer piezoelectric element 100.

[0061] 9 is a schematic diagram showing an example of the general configuration of an ultrasonic scalpel 450 serving as the device 150. The ultrasonic scalpel 450 includes an ultrasonic vibrator 460 and an operating member 470. The ultrasonic vibrator 460 has a piezoelectric element 50 or a laminated piezoelectric element 100, and is driven to generate ultrasonic vibrations when an electrical signal is applied. The ultrasonic vibrator 460 operates to transmit ultrasonic vibrations to an operating member 470 configured in a shaft shape. The ultrasonic vibrator 460 drives the operating member 470 so as to perform an action of incising, ablating, or thermocoagulating hemostasis on biological tissue in the vicinity of the operating member 470.

[0062] 10 is a schematic diagram showing an example of the general configuration of an ultrasonic scaler 500 as the device 150. The ultrasonic scaler 500 includes an ultrasonic vibrator 460 and a dental tip 510. The ultrasonic vibrator 460 has a piezoelectric element 50 or a multilayer piezoelectric element 100, and is driven to generate ultrasonic vibrations when an electrical signal is applied. The ultrasonic vibrator 460 operates to transmit ultrasonic vibrations to the dental tip 510.

[0063] 11 is a schematic diagram showing an example of the schematic configuration of an ultrasonic cleaning machine 550 as the apparatus 150. The ultrasonic cleaning machine 550 includes an ultrasonic vibrator 460 and a cleaning container 560. The ultrasonic vibrator 460 has a piezoelectric element 50 or a multilayer piezoelectric element 100, and is driven to generate ultrasonic vibrations when an electric signal is applied. An object 570 to be cleaned is placed in the cleaning container 560 containing a cleaning liquid, and the ultrasonic vibrator 460 is vibrated to generate ultrasonic vibrations, which are transmitted to the cleaning liquid, thereby cleaning the object 570 to be cleaned.

[0064] 12 is a schematic diagram showing an example of the general configuration of an ultrasonic processing machine 600 as the apparatus 150. The ultrasonic processing machine 600 includes a substrate 610, an ultrasonic vibrator 460, a grinding stone unit 620, and a spindle 630. The substrate 610 is disk-shaped, and the grinding stone unit 620 is formed on its outer periphery. The center of the substrate 610 is fixed to the spindle 630.

[0065] The ultrasonic vibrator 460 has a piezoelectric element 50 or a laminated piezoelectric element 100, and is driven to generate ultrasonic vibrations when an electric signal is applied. The driving direction of the ultrasonic vibrator 460 is the radial direction from the center of the substrate 610 to the periphery. While the ultrasonic vibrator 460 generates vibrations, the spindle 630 is rotated about its axial direction, and the grinding stone portion 620 formed on the periphery of the substrate 610 is pressed against the workpiece, thereby cutting the workpiece.

[0066] 13 is a schematic diagram showing an example of a schematic configuration of a piezoelectric transducer 650 as the device 150. The piezoelectric transducer 650 includes a piezoelectric element 50 or a multilayer piezoelectric element 100.

[0067] 14 is a schematic diagram showing an example of the general configuration of an ultrasonic motor 700 as the device 150. The ultrasonic motor 700 includes an ultrasonic vibrator 460, a rotor 710, and an output shaft 720. The ultrasonic vibrator 460 has a piezoelectric element 50 or a multilayer piezoelectric element 100. For example, when an AC voltage is applied to the piezoelectric element 50 or the multilayer piezoelectric element 100, a bending traveling wave is generated in the ultrasonic vibrator 460, and each point on the sliding surface of the ultrasonic vibrator 460 performs an elliptical motion. When the rotor 710 is pressed against the sliding surface of the ultrasonic vibrator 460, the rotor 710 receives a frictional force from the ultrasonic vibrator 460 and rotates in the opposite direction to the bending traveling wave.

[0068] [Manufacturing method of piezoelectric element] An example of a method for manufacturing the piezoelectric element 50 will be described below.

[0069] (Method for producing calcined powder of main phase) First, the raw materials for the main phase of the lead-free piezoelectric ceramic composition are mixed. Here, the necessary raw material powders for the main phase are selected and weighed to achieve the desired composition. The raw material powders can be oxides, carbonates, or hydroxides of the elements contained in the perovskite-type oxides, primarily composed of K, Na, and Nb, that constitute the main phase. Specifically, K2CO3 powder, Na2CO3 powder, Li2CO3 powder, CaCO3 powder, SrCO3 powder, BaCO3 powder, Nb2O5 powder, TiO2 powder, ZrO2 powder, etc. are suitable. Ethanol is then added to these raw material powders, and the mixture is wet-mixed in a ball mill for preferably 15 hours or more to obtain a slurry. The slurry is then dried to obtain a mixed powder, which is then calcined, for example, at 600 to 1000°C in an air atmosphere for 1 to 10 hours to produce a calcined powder for the main phase.

[0070] In the above description, the calcined powder is produced by mixing the raw materials of the main phase and calcining, but other configurations are also possible. For example, the raw material powders may be mixed and fired multiple times. Specifically, first, raw material powders containing several elements that are part of the elements contained in the target perovskite oxide mainly composed of K, Na, and Nb are mixed and calcined to obtain calcined powder 1. Then, the obtained calcined powder 1 is mixed with raw material powders containing the remaining elements contained in the target alkali niobate perovskite oxide, and further calcined. In this manner, the calcined powder of the main phase may be produced.

[0071] (Method for producing calcined subphase powder) Separately from the mixing of the raw materials for the main phase, raw materials for the subphase of the lead-free piezoelectric ceramic composition are mixed. Here, necessary raw material powders for the subphase are selected and weighed to achieve the desired composition. The raw material powders can be, for example, oxides, carbonates, or hydroxides of the elements contained in the compound having a tungsten bronze structure that constitutes the subphase. Specifically, BaCO3 powder, CaCO3 powder, SrCO3 powder, Na2CO3 powder, K2CO3 powder, Nb2O5 powder, etc. are selected as needed and weighed. Ethanol is then added to these raw material powders, and the mixture is wet-mixed in a ball mill to obtain a slurry. The wet mixing using a ball mill is preferably carried out for 15 hours or more. The slurry is then dried to obtain a mixed powder, which 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.

[0072] (Method for producing sintered body) Ethanol and a binder are added to the calcined powder of the main phase, or the calcined powder of the main phase and the calcined powder of the subphase, prepared as described above, and wet-mixed in a ball mill to obtain a slurry. The slurry is then dried to produce a granulated powder. The granulated powder is then filled into a mold and uniaxially pressed at a pressure of, for example, 20 MPa to form it into a desired shape. A CIP (cold isostatic pressing) process is then performed at a pressure of, for example, 150 MPa to obtain a compact. The obtained compact (CIP pressed compact) is then fired, for example, at 900°C to 1300°C in an air atmosphere for 1 to 10 hours, to obtain a piezoelectric body from the piezoelectric ceramic composition.

[0073] At this time, the temperature rise rate is adjusted to 300°C / hour to 700°C / hour. By controlling the firing temperature and holding time while maintaining the temperature rise rate as described above, domains separated by Σ=n symmetric tilt grain boundaries (n is an odd number of 5 or more) are generated in the main phase of the lead-free piezoelectric ceramic composition.

[0074] (Processing method) Next, the obtained piezoelectric body is cut and the top and bottom surfaces are processed according to the dimensional accuracy required for the piezoelectric element. To stabilize the characteristics of the obtained piezoelectric body, for example, it is annealed in air at 100°C for 2 hours. Thereafter, electrodes 71 and 72 are formed on the surface of the obtained piezoelectric body 60 by, for example, a sputtering method, and a polarization process is performed to obtain the piezoelectric element 50.

[0075] The above-described manufacturing method is merely an example, and various other steps and processing conditions can be used to manufacture the piezoelectric element 50. For example, 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 corresponding to the final composition of the lead-free piezoelectric ceramic composition, and then fired. However, if the calcined products of the main phase and subphase are separately produced and then mixed, the compositions of the main phase and subphase can be more strictly controlled, and therefore the yield of the lead-free piezoelectric ceramic composition can be increased.

[0076] [Manufacturing method of multilayer piezoelectric element] Next, an example of a method for manufacturing the multilayer piezoelectric element 100 will be described below.

[0077] (Method for producing calcined powder of main phase and subphase) The method for producing the calcined powder of the main phase and the calcined powder of the subphase is the same as that described above, and therefore the explanation will be omitted.

[0078] (Method for manufacturing a multilayer piezoelectric element) The calcined powder of the main phase or the calcined powder of the main phase and the calcined powder of the subphase prepared as described above is 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. When a subphase is added, 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 the like to produce a ceramic green sheet.

[0079] 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 preferably contains nickel (Ni) as its main component.

[0080] Next, 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 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 condition of 200 to 400°C for 2 to 10 hours. At this time, the oxygen partial pressure is controlled as necessary to suppress oxidation of the electrode layers.

[0081] After the binder removal treatment, the laminate is heated at a temperature of, for example, 900 to 1300°C. acid The partial pressure is 10 -12 The mixture is fired in a reducing atmosphere of about atm% for 1 to 10 hours.

[0082] At this time, the heating rate is adjusted to 300°C / hour to 700°C / hour. By controlling the heating rate within the above range while controlling the firing temperature and holding time, domains separated by Σ=n symmetrical tilt grain boundaries (n is an odd number of 5 or more) are generated in the main phase of the lead-free piezoelectric ceramic composition.

[0083] After the fired laminate has been polished appropriately, 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 interposed therebetween. The laminate with the external electrodes 106, 107 formed thereon is subjected to a polarization process, thereby obtaining a multilayer piezoelectric element 100. In this manner, a multilayer piezoelectric element 100 is obtained, having a structure in which piezoelectric layers 103 made of the lead-free piezoelectric composition of the present invention and internal electrodes 104, 105 are alternately stacked.

[0084] The above-described manufacturing method is an example, and various other steps and processing conditions for manufacturing the multilayered piezoelectric element 100 can be used.

[0085] [Examples and Comparative Examples] (Example) The composition of the main phase is (K 0.48 Na 0.48 Ba 0.02 Ca 0.02 )(Nb 0.94 Ti 0.04 Mn 0.02 K2CO3 powder, Na2CO3 powder, Ba2CO3 powder, CaCO3 powder, Nb2O5 powder, TiO2 powder, and MnCO3 powder were weighed as raw material powders for the main phase so that the composition would be 0.03. Ethanol was added to these raw material powders for 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 at 930°C for 4 hours in an air atmosphere to produce the calcined powder for the main phase.

[0086] Separately, the subphase composition is Ba2KNbO 15 BaCO3 powder, KCO3 powder, and Nb2O5 powder were weighed as raw material powders for the subphase so that the composition satisfies the following formula. Ethanol was added to these raw material powders for the subphase, and they were wet mixed in a ball mill for 15 hours or more to obtain a slurry. The mixed powder obtained by drying the slurry was calcined at 1100°C for 5 hours in an air atmosphere to produce the calcined powder of the subphase.

[0087] Next, the calcined powder of the main phase and the calcined powder of the subphase were weighed so that the ratio of the calcined powder of the subphase to the calcined powder of the main phase was 2.0 vol%. Next, ethanol and a binder were added to the weighed calcined powder of the main phase and the calcined powder of the subphase, and the mixture was wet-mixed in a ball mill for 15 hours or more to obtain a slurry. The slurry was then dried to obtain a granulated powder. The granulated powder was then uniaxially pressed at a pressure of 20 MPa to form a disk-like shape. A CIP (cold isostatic pressing) process was then performed at a pressure of 150 MPa to obtain a compact. The obtained compact (CIP pressed compact) was fired in an air atmosphere to obtain a piezoelectric element of the example. The firing conditions were a temperature rise rate of 500°C / hour and a maximum temperature of 1130°C held for 3 hours.

[0088] Next, the obtained piezoelectric body was cut and the top and bottom surfaces were processed according to the dimensional accuracy required for the piezoelectric element. To stabilize the characteristics of the obtained piezoelectric body, it was annealed in air at 100°C for 2 hours. After that, electrodes were attached by sputtering, and a polarization process was performed to produce the piezoelectric element of the example.

[0089] (Comparative Example) The piezoelectric element of the comparative example was produced under the same conditions as the piezoelectric element of the example except that the firing condition was adjusted to a temperature rise rate of 200° C. / hour.

[0090] [Σ=n symmetrical tilt grain boundary confirmation] The piezoelectric elements of the examples and comparative examples were prepared as samples for transmission electron microscopy as follows. First, the sample was polished using waterproof abrasive paper until the sample film thickness was approximately 50 μm. Next, the sample was ground into a cone shape using a dimple grinder so that the sample film thickness at the center was approximately 20 μm. After that, an ion milling machine was used to penetrate the sample near the center, cutting the sample into a wedge-shaped thin section.

[0091] The prepared samples were evaluated using a transmission electron microscope (JEOL, JEM-F200). Transmission electron microscope images were collected at 400,000 magnifications of perovskite-type oxide crystal grains whose crystal orientation was adjusted to the

[0100] direction and whose main components were K, Na, and Nb. Electron diffraction images of the same grains were collected with a camera length of 500 mm. The presence or absence of Σ=n symmetric tilt grain boundaries was determined by analyzing the atomic arrangement and diffraction spots from transmission electron microscope images and electron diffraction.

[0092] [Coupling coefficient measurement] The piezoelectric elements of the examples and comparative examples were measured using an impedance analyzer (E4990A, manufactured by Keysight Technologies), and the coupling coefficient was determined by the resonance-antiresonance method.

[0093] [result] Figures 15(a) and (b) are transmission electron microscope images of crystal grains of a perovskite oxide containing K, Na, and Nb as its main components, respectively, according to the example. Figure 15(a) is a 40,000-magnification transmission electron microscope image, and Figure 15(b) is a 400,000-magnification transmission electron microscope image. The white line in Figure 15(a) is the boundary between two domains in the perovskite oxide containing K, Na, and Nb as its main components, separated by θ degrees. When this boundary was examined at a higher magnification, Figure 15(b) revealed that it was a Σ=n symmetric tilt grain boundary. This confirmed that the piezoelectric element of the example had domains separated by a Σ=n symmetric tilt grain boundary in the main phase.

[0094] Figures 16(a) and 16(b) show electron diffraction spot images and explanations of two adjacent domains containing the Σ=n symmetric tilt grain boundary of the example. Figures 16(a) and 16(b) show that the diffraction spots of each domain of the example have a rotational relationship of approximately 53°. Therefore, when the Σ=n symmetric tilt grain boundary of the example is indexed as a pseudo-cubic perovskite structure, the {210} diffraction spots overlap. These results confirm that the Σ=n symmetric tilt grain boundary of the crystal grains of the main phase of the example piezoelectric element is a Σ=5 {210} symmetric tilt grain boundary.

[0095] The coupling coefficient of the piezoelectric element of the comparative example was 18%, while the coupling coefficient of the piezoelectric element of the example was a very high value of 40%, which confirmed that the lead-free piezoelectric ceramic composition and piezoelectric element of the present invention can cope with a wide range of applied voltages and can obtain high output.

[0096] This confirmed that the formation of symmetric tilt grain boundaries can be controlled by adjusting the heating temperature, firing temperature, and holding time. Among these conditions, the heating rate is presumed to be particularly important for the formation of symmetric tilt grain boundaries.

[0097] From the above results, it was confirmed that the lead-free piezoelectric ceramic composition, piezoelectric element, and device using the same of the present invention can improve the coupling coefficient, can accommodate a wide range of applied voltages, and can produce high output.

[0098] 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]

[0099] 50 Piezoelectric element 60 Piezoelectric 71, 72 electrode 100 Multilayer piezoelectric element 103 Piezoelectric 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 350 Buzzer 360 cases 362 Support Ring 364 Top Plate 370 Piezoelectric diaphragm 380 Sound emission hole 390 Resonance space 400 ultrasonic sensor 410 Cylindrical case with bottom 412 Opening 420 Acoustic matching layer 430 Base material 441, 442 input / output terminals 450 Ultrasonic scalpel 460 Ultrasonic Transducer 470 Working member 500 Ultrasonic Scaler 510 Dental Tip 550 Ultrasonic Cleaner 560 Cleaning container 570 Items to be washed 600 Ultrasonic processing machine 610 Base material 620 Grindstone Department 630 Spindle 650 Piezoelectric Transducer 700 ultrasonic motor 710 rotor 720 output shaft D1 Stacking direction

Claims

1. A lead-free piezoelectric ceramic composition containing at least a main phase of a perovskite-type oxide containing K, Na, and Nb as main components, A lead-free piezoelectric ceramic composition characterized in that the main phase contains domains separated by Σ=n symmetrical tilt grain boundaries (n is an odd number of 5 or more).

2. 2. The lead-free piezoelectric ceramic composition according to claim 1, wherein, in an electron diffraction pattern of two domains sandwiching the boundary of the Σ=n symmetric tilt grain boundary, when indexed as a pseudo-cubic perovskite structure, the respective {210} diffraction spots overlap with each other.

3. A piezoelectric element comprising a piezoelectric body made of the lead-free piezoelectric ceramic composition according to claim 1 or 2, and electrodes in contact with the piezoelectric body.

4. A device comprising the piezoelectric element of claim 3 .

5. The device of claim 4 , which is selected from the group consisting of an actuator, a haptic, a buzzer, an ultrasonic sensor, an ultrasonic scalpel, an ultrasonic scaler, an ultrasonic cleaner, an ultrasonic processing machine, a piezoelectric transducer, and an ultrasonic motor.

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