Lead-free piezoelectric composition, piezoelectric device, and apparatus

Abstract

To suppress a change rate of a mechanical quality factor Qm between a low load and high load in an alkali niobate-based perovskite oxide.SOLUTION: A lead-free piezoelectric composition comprises: a main phase consisting of alkali niobate-based perovskite-type oxides; and a sub-phase including metal oxides different from the alkali niobate-based perovskite-type oxides constituting the main phase, wherein the Young's modulus is 90 GPa or more.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present disclosure relates to a lead-free piezoelectric composition, a piezoelectric element, and a device.

Background Art

[0002] Conventionally, as a composition exhibiting piezoelectricity, a PZT-based (lead zirconate titanate-based) composition has been widely used. However, due to the reduction of environmental impact, the development of a lead-free piezoelectric composition that does not use lead is desired. As candidates for such a lead-free piezoelectric composition, for example, alkali niobate-based perovskite oxides have been proposed. Specifically, in Patent Documents 1 and 2, by specifying the composition of a piezoelectric material (KNN-based piezoelectric material) containing a compound represented by K x Na (1-x) NbO3 as a main component, a configuration for improving piezoelectric properties such as the mechanical quality factor Qm has been disclosed. The mechanical quality factor Qm is a parameter representing the sharpness of mechanical vibration (sharpness of the resonance spectrum) near the resonance frequency when the piezoelectric composition causes natural vibration. The larger the mechanical quality factor Qm, the lower the loss, and the efficiency of an actuator provided with the piezoelectric composition can be increased.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In such lead-free piezoelectric compositions, further improvement in piezoelectric properties is required. Regarding the mechanical quality factor Qm, it is desirable that the rate of change of Qm from low load to high load (from low vibration stress to high vibration stress) be smaller. That is, generally, as the load increases, Qm decreases. Therefore, particularly in applications that require driving under high loads, it is desired to minimize the decrease in Qm when the load increases. However, with respect to configurations for suppressing the rate of change of the mechanical quality factor Qm between low load and high load in alkali niobate perovskite oxides, sufficient investigations have not been conducted.

Means for Solving the Problems

[0005] The present disclosure can be realized in the following forms. [1] According to one aspect of the present disclosure, a lead-free piezoelectric composition is provided. This lead-free piezoelectric composition includes a main phase composed of an alkali niobate perovskite-type oxide and a sub-phase containing a metal oxide different from the alkali niobate perovskite-type oxide constituting the main phase, and has a Young's modulus of 90 GPa or more. According to the lead-free piezoelectric composition of this aspect, by setting the Young's modulus of the lead-free piezoelectric composition including a main phase composed of an alkali niobate perovskite-type oxide and a sub-phase containing a metal oxide different from the alkali niobate perovskite-type oxide constituting the main phase to 90 GPa or more, the rate of change of the mechanical quality factor Qm between low load and high load (low vibration stress and high vibration stress) can be suppressed. Therefore, it becomes possible to obtain a piezoelectric element with stable piezoelectric properties from low load to high load. [2] In the lead-free piezoelectric composition of the above aspect, the Young's modulus may be 100 GPa or more. With such a configuration, the effect of suppressing the rate of change of the mechanical quality factor Qm can be further enhanced. [3] In the lead-free piezoelectric composition of the above aspect, the Young's modulus may be 105 GPa or more. With such a configuration, the effect of suppressing the rate of change of the mechanical quality factor Qm can be further enhanced. [4]In the lead-free piezoelectric composition of the above-described embodiment, the metal oxide constituting the secondary phase may include at least one of a metal oxide having a spinel-type structure and a metal oxide having a tungsten bronze-type structure. With such a configuration, the sinterability of the lead-free piezoelectric composition can be improved. [5]In the lead-free piezoelectric composition of the above-described embodiment, the alkali niobate-based perovskite-type oxide constituting the primary phase has a composition formula (A1 a M1 b ) c (Nb d1 M2 d2 M3 d3 )O 3+e (wherein element A1 is at least one of alkali metals, element M1 is at least one of Ba, Ca, and Sr, element M2 is at least one of Ti, Zr, Ta, Hf, Sn, Sb, and Si, element M3 is at least one of Mn, Mg, Al, Sc, Fe, Co, Ni, Zn, Ga, and Y, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, d1 + d2 + d3 = 1, and e represents a value of oxygen deficiency or excess). It may be an alkali niobate-based perovskite-type oxide represented by this. With such a configuration, the mechanical quality factor Qm in the lead-free piezoelectric composition can be increased. [6]In the lead-free piezoelectric composition of the above-described embodiment, element A1 may be at least one of K and Na, element M2 may be at least one of Ti and Zr, element M3 may be Mn, and 0 < a ≤ 1. With such a configuration, it becomes easy to enhance the piezoelectric properties in the lead-free piezoelectric composition. [7]According to another embodiment of the present disclosure, there is provided a piezoelectric element including a piezoelectric body formed of the lead-free piezoelectric composition according to any one of [1] to [6] above, and an electrode attached to the piezoelectric body. According to the piezoelectric element of this embodiment, the piezoelectric properties of the piezoelectric element can be stabilized from low load to high load. As a result, the energy loss in driving at high load can be reduced, and stable driving can be performed. [8]According to still another aspect of the present disclosure, there is provided an apparatus including the piezoelectric element described in [7]. According to the apparatus of this aspect, since it includes a piezoelectric element including a lead-free piezoelectric composition having stable piezoelectric characteristics from low load to high load, the performance of the entire apparatus can be improved. The present disclosure can be implemented in various forms. For example, it can be implemented in the forms of a lead-free piezoelectric composition, a piezoelectric element using the same, various apparatuses including the piezoelectric element (ultrasonic scalpel, ultrasonic scaler, ultrasonic cleaner, ultrasonic processing machine, piezoelectric transducer, ultrasonic motor, piezoelectric gyro sensor, piezoelectric filter, knock sensor, etc.), and a method for manufacturing a lead-free piezoelectric composition.

Brief Description of the Drawings

[0006]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Figure 13

Mode for Carrying Out the Invention

[0007] A. Lead-free piezoelectric composition: The lead-free piezoelectric composition of this embodiment includes a main phase composed of an alkali niobate-based perovskite-type oxide and a sub-phase containing a metal oxide different from the alkali niobate-based perovskite-type oxide constituting the main phase. And the lead-free piezoelectric composition of this embodiment has a Young's modulus of 90 GPa or more.

[0008] (A-1) Regarding the main phase: The alkali niobate-based perovskite oxide constituting the main phase preferably contains at least one of alkali metals (such as potassium (K), sodium (Na), lithium (Li), etc.) as an alkali component, and particularly preferably contains at least one of potassium (K) and sodium (Na). Further, the alkali niobate-based perovskite oxide constituting the main phase may contain at least one of alkaline earth metals (such as calcium (Ca), strontium (Sr), barium (Ba), etc.) as an alkali component.

[0009] The alkali niobate-based perovskite-type oxide constituting such a main phase may contain manganese (Mn). It is considered that the mechanical quality factor Qm is improved by the solid solution of manganese (Mn) as an acceptor at the niobium site (B site of the perovskite-type crystal structure). However, manganese (Mn) is not essential.

[0010] Further, the alkali niobate-based perovskite oxide constituting the main phase is preferably an alkali niobate-based perovskite-type oxide that satisfies the following compositional formula (1).

[0011] (A1 a M1 b ) c (Nb d1 M2 d2 M3 d3 )O 3+e … (1)

[0012] However, in the formula, element A1 is at least one of alkali metals, element M1 is at least one of Ba, Ca, and Sr, element M2 is at least one of Ti, Zr, Ta, Hf, Sn, Sb, and Si, element M3 is at least one of Mn, Mg, Al, Sc, Fe, Co, Ni, Zn, Ga, and Y, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, d1 + d2 + d3 = 1, and e is a value indicating oxygen deficiency or excess.

[0013] In the above composition formula (1), element A1 and element M1 are arranged at the A site of the perovskite structure, and Nb (niobium), element M2, and element M3 are arranged at the B site. As the values of the coefficients a, b, d1 to d3, and e in the above composition formula (1), among the combinations of values for which the perovskite structure is established, preferred values from the viewpoints of the electrical and piezoelectric properties of the lead-free piezoelectric composition are selected within the ranges described above. In the alkali niobate perovskite oxide represented by composition formula (1), d1 = 0 (a composition not containing Nb) is excluded. Further, the alkali niobate perovskite oxide represented by composition formula (1) contains at least one of element M2 and element M3.

[0014] Among the oxygen coefficients (3 + e), the coefficient e is a positive or negative value indicating oxygen deficiency or excess with respect to the oxygen coefficient that is usually 3. The oxygen coefficient (3 + e) can take a value for which the main phase constitutes a perovskite oxide. A typical value of the coefficient e is e = 0, and -0.1 ≤ e ≤ 0.1 is preferred. Note that 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.

[0015] In the above compositional formula (1), element A1 is at least one of K and Na, element M2 is at least one of Ti and Zr, element M3 is Mn, and it may be 0 < a ≤ 1. With such a configuration, it becomes easy to enhance the piezoelectric properties of the lead-free piezoelectric composition. Such an alkali niobate perovskite-type oxide can be represented by the following compositional formula (2).

[0016] ((K a1 Na a2 )(Ba b1 Ca b2 Sr b3 )) c (Nb d1 (Ti d2x Zr d2y )Mn d3 )O 3+e … (2)

[0017] However, in the formula, a1 + a2 = a, b1 + b2 + b3 = b, d2x + d2y = d2. a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, d1 + d2 + d3 = 1, e is a value indicating oxygen deficiency or excess, and -0.1 ≤ e ≤ 0.1 is preferable.

[0018] At this time, in particular, for element A1, 0 < a1 < 1 and 0 < a2 < 1, for element M1, 0 ≤ b1 ≤ 0.2, 0 ≤ b2 ≤ 0.2, 0 ≤ b3 ≤ 0.2, for element M2, 0 ≤ d2x ≤ 0.2, 0 ≤ d2y ≤ 0.2, and for Mn, 0 ≤ d3 ≤ 0.1 are desirable. Thereby, the piezoelectric properties of the lead-free piezoelectric composition can be further enhanced. Also, for element A1, 0 < a1 ≤ 0.7 and 0.3 ≤ a2 < 1, for element M1, 0 ≤ b1 ≤ 0.1, 0 ≤ b2 ≤ 0.1, 0 ≤ b3 ≤ 0.1, for element M2, 0 ≤ d2x ≤ 0.1, 0 ≤ d2y ≤ 0.1, and for Mn, 0 ≤ d3 ≤ 0.08 are more desirable. Thereby, the piezoelectric properties of the lead-free piezoelectric composition can be further enhanced.

[0019] (A-2) Regarding the secondary phase: The metal oxide constituting the secondary phase is a metal oxide different from the alkali niobate perovskite-type oxide constituting the primary phase. By providing such a secondary phase, for example, the sinterability in a lead-free piezoelectric composition can be improved. Further, the coexistence of the secondary phase with the primary phase can stabilize the crystal structure of the primary phase and improve the piezoelectric properties. Also, the secondary phase can suppress the occurrence of a rapid property change caused by the presence of a phase transition point between -50°C and +150°C in the lead-free piezoelectric composition. Note that the secondary phase may contain one type of metal oxide or a plurality of types of metal oxides as metal oxides different from the alkali niobate perovskite-type oxide. Further, the secondary phase may contain a crystal phase different from the crystal phase of the above-described metal oxide or may contain impurity elements.

[0020] The metal oxide constituting such a secondary phase can be, for example, at least one of a metal oxide having a spinel-type structure and a metal oxide having a tungsten bronze-type structure. Also, the metal oxide constituting the secondary phase, in addition to or instead of the above metal oxide, can be at least one of an A2B6O 13 system compound (element A is a monovalent metal, element B is a metal having a valence of 2 to 6), and an A-Ti-B-O system compound (element A is an alkali metal, element B is at least one of Nb and Ta).

[0021] In the present specification, the "metal oxide having a spinel-type structure" includes both a normal spinel compound having a normal spinel-type crystal structure and an inverse spinel compound having an inverse spinel-type crystal structure. Here, the metal oxide having a spinel-type structure can be, for example, an M-Ti-O system spinel compound, and preferably a compound represented by the following formula (3).

[0022] M x TiO y … (3)

[0023] In the above formula (3), the element M is a metal element with a valence of 1 to 4, and is at least one of lithium (Li), magnesium (Mg), aluminum (Al), scandium (Sc), chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), zinc (Zn), gallium (Ga), yttrium (Y), zirconium (Zr), tin (Sn), antimony (Sb), silicon (Si), hafnium (Hf). When Li is included as the element M, in order for the compound of formula (3) to form a spinel-type crystal structure, it is preferable that one or more metal elements other than Li among the above metal elements are included together with Li. The coefficients x and y are relative values when the Ti content is set to 1. In order for the compound of formula (3) to form a spinel compound, it is preferable that the coefficient x satisfies 0.5 ≤ x ≤ 5.0. Also, the coefficient y is an arbitrary value for forming a spinel compound, but typically it is preferable that 2 ≤ y ≤ 8 is satisfied. The coefficients x and y may deviate from the above standard values as long as they can maintain the spinel-type crystal structure and the change in the properties of the compound is acceptable. From the viewpoint of piezoelectric properties, the compound of formula (3) is preferably a compound of the composition formula M2TiO4 containing two divalent metal elements M, or a compound represented by (M1,M2)TiO4 containing two types of metal elements M.

[0024] Also, the compound having a tungsten bronze-type structure is a compound represented by the following formula (4).

[0025] A h B i O 15+δ … (4)

[0026] In the above formula (4), element A contains two or more elements with a valence of 1 to 2, and element B contains one or more elements with a valence of 2 to 5. Element A is preferably at least one of sodium (Na), potassium (K), lithium (Li), barium (Ba), calcium (Ca), and strontium (Sr). Also, element B is preferably at least one of niobium (Nb), manganese (Mn), iron (Fe), nickel (Ni), cobalt (Co), zinc (Zr), and zirconium (Zr). Further, for h, i, and δ, although h = 3, i = 5, and δ = 0 are standard, as long as the tungsten bronze-type crystal structure can be maintained and the change in the properties of the compound is within an acceptable range, they may deviate from the above standard values, and they may also contain impurity elements. As specific examples of the compound represented by the above formula (4), element B is preferably Nb. For example, Ba2KNb5O 15 , Ba2NaNb5O 15 , Ca2KNb5O 15 , Ca2NaNb5O 15 etc. can be cited.

[0027] As for the A2B6O 13 series compounds, compounds in which element A (a monovalent metal) is at least one of Li, Na, and K, and element B (a metal with a valence of 2 to 6) is at least one of Co, Fe, Mg, Ni, Zr, Mn, Al, Nb, Ta, and W can be used. Specifically, for example, K2(Ti,Nb,Mg)6O 13 , K2(Ti,Nb,Co,Zn)6O 13 etc. can be used.

[0028] As for the A-Ti-B-O series compounds, those having the following composition of formula (5) or (6) can be used.

[0029] A 1-x Ti 1-x B 1+x O5… (5) A1Ti3B1O9… (6)

[0030] Here, element A is at least one of alkali metals (such as potassium (K), rubidium (Rb), cesium (Cs), etc.), and element B is at least one of niobium (Nb) and tantalum (Ta). The coefficient x in the above formula (5) is an arbitrary value. However, it is preferable that the coefficient x satisfies 0 ≦ x ≦ 0.15. If the coefficient x takes a value within this range, the structure of the compound is stable and a uniform crystal phase can be obtained.

[0031] Metal oxides such as oxides having a spinel-type structure constituting the above-described secondary phase and compounds having a tungsten bronze-type structure generally do not have piezoelectric properties. However, by being mixed with the main phase composed of an alkali niobate perovskite oxide, the sinterability of the piezoelectric composition can be improved. From the viewpoint of ensuring the effect of enhancing the sinterability of the lead-free piezoelectric composition, the content ratio of the secondary phase is desirably 0.3% by volume or more, and more desirably 0.5% by volume or more. Further, from the viewpoint of ensuring the piezoelectric properties of the lead-free piezoelectric composition, the content ratio of the secondary phase is desirably 10% by volume or less, and more desirably 7% by volume or less. It should be noted that regarding the type of compound constituting the secondary phase, such as the metal oxide having a spinel-type structure or the metal oxide having a tungsten bronze-type structure, it can be determined by performing Rietveld Analysis using the diffraction results of powder X-ray diffraction (XRD).

[0032] (A-3) Regarding Young's modulus: As described above, the Young's modulus of the lead-free piezoelectric composition of this embodiment is 90 GPa or more. By setting the Young's modulus within the above range, in the lead-free piezoelectric composition, the change rate of the mechanical quality factor Qm between low load and high load (low vibration stress and high vibration stress) can be suppressed. The change rate of the mechanical quality factor Qm between low load and high load can be calculated and evaluated, for example, by defining the vibration stress Tm = 1 MPa as the low load, defining the vibration stress Tm = 20 MPa as the high load, and using the value of Qm at Tm = 1 MPa and the value of Qm at Tm = 20 MPa. The reason for obtaining the effect of suppressing the change rate of the mechanical quality factor Qm is considered to be that the hardness of the lead-free piezoelectric composition is ensured by setting the Young's modulus within the above range, and as a result, the structure of the ceramic constituting the lead-free piezoelectric composition, specifically, the domain structure within the particles, etc. is stabilized. From the viewpoint of obtaining the above effect by increasing the Young's modulus of the lead-free piezoelectric composition to ensure the hardness of the lead-free piezoelectric composition, the Young's modulus of the lead-free piezoelectric composition is preferably 100 GPa or more, more preferably 105 GPa or more, and even more preferably 120 GPa or more.

[0033] On the other hand, when the Young's modulus of the lead-free piezoelectric composition increases and the lead-free piezoelectric composition becomes excessively hard, it becomes difficult for the lead-free piezoelectric composition to vibrate, so the piezoelectric performance of the piezoelectric element including the lead-free piezoelectric composition may decrease. Therefore, from the viewpoint of suppressing the above-described decrease in piezoelectric performance, the Young's modulus of the lead-free piezoelectric composition is preferably, for example, 150 GPa or less, more preferably 140 GPa or less, and even more preferably 130 GPa or less.

[0034] The Young's modulus of the lead-free piezoelectric composition can be adjusted, for example, by the composition of the main phase and the secondary phase constituting the lead-free piezoelectric composition, particularly the composition of the main phase with a higher content ratio in the lead-free piezoelectric composition. Also, the Young's modulus of the lead-free piezoelectric composition can be adjusted by the manufacturing conditions of the lead-free piezoelectric composition, particularly the firing temperature when producing the lead-free piezoelectric composition. For example, the higher the firing temperature, specifically the maximum temperature during firing, the greater the Young's modulus of the lead-free piezoelectric composition can be made.

[0035] B. Piezoelectric element: (B-1) Structure of piezoelectric element: FIG. 1 is a perspective view showing the appearance of a piezoelectric element 10 according to the present embodiment. This piezoelectric element 10 includes a piezoelectric body 20 formed of the lead-free piezoelectric composition of the present embodiment and electrodes 31 and 32. This piezoelectric element 10 has a configuration in which the electrodes 31 and 32 are attached to the upper surface and the lower surface of the disk-shaped piezoelectric body 20. Note that, as the piezoelectric element, piezoelectric elements having various other shapes and configurations can be formed.

[0036] (B-2) Manufacturing method of piezoelectric element: FIG. 2 is a flowchart showing an example of the manufacturing method of the piezoelectric element 10. When manufacturing the piezoelectric element 10, first, raw material mixing of the main phase of the lead-free piezoelectric composition is performed (step T110). Here, the necessary raw material powders of the main phase are selected and weighed so as to obtain the target composition. The raw material powders can be oxides, carbonates, and hydroxides of the respective elements contained in the alkali niobate-based perovskite oxide constituting the main phase. Specifically, K2CO3 powder, Na2CO3 powder, Li2CO3 powder, CaCO3 powder, SrCO3 powder, BaCO3 powder, Nb2O5 powder, TiO2 powder, ZrO2 powder, etc. can be preferably used. In step T110, ethanol is added to the above-mentioned raw material powders, and wet mixing is preferably performed for 15 hours or more in a ball mill to obtain a slurry. Then, the slurry is dried to obtain a mixed powder, and the obtained mixed powder is calcined, for example, at 600 to 1000 ° C. in an air atmosphere for 1 to 10 hours to produce a calcined powder of the main phase (step T120).

[0037] In the above description, the calcined powder is produced by mixing the raw materials in step T110 and calcining in step T120. However, a different configuration may also be used. For example, the operation of mixing and firing the raw material powder may be performed multiple times. Specifically, first, a plurality of types of raw material powders containing some of the elements included in the target alkali niobate perovskite oxide are mixed and calcined to obtain calcined powder 1. Then, with respect to the obtained calcined powder 1, raw material powders containing the remaining elements among the elements included in the target alkali niobate perovskite oxide are mixed and further calcined to obtain calcined powder 2. In this way, the calcined powder of the main phase may be produced.

[0038] Also, separately from the above-described step T110, raw materials for the secondary phase of the lead-free piezoelectric composition are mixed (step T130). Here, the necessary materials are selected as the raw material powders for the secondary phase and weighed to obtain the target composition. The raw material powders can be oxides, carbonates, or hydroxides of each element contained in metal oxides such as oxides having a spinel-type structure or oxides having a tungsten bronze-type structure that constitute the secondary phase. Specifically, raw material powders are selected and weighed as needed from BaCO3 powder, CO3 powder, SrCO3 powder, Na2CO3 powder, K2CO3 powder, Nb2O5 powder, Co3O4 powder, ZnO powder, TiO2 powder, etc. Then, ethanol is added to these raw material powders and wet-mixed in a ball mill to obtain a slurry. The wet mixing using a ball mill is preferably performed for 15 hours or more. Thereafter, the slurry is dried to obtain a mixed powder, and the obtained mixed powder is calcined, for example, at 600 to 1300 °C in an air atmosphere for 1 to 10 hours to produce a calcined powder of the secondary phase (step T140).

[0039] Thereafter, the calcined powder of the main phase obtained in step T120 and the calcined powder of the secondary phase obtained in step T140 are each weighed, a binder and ethanol are added, and wet mixing is performed using a ball mill to obtain a slurry. Then, the obtained slurry is dried, granulated, and molded (step T150). Specifically, for example, by performing uniaxial pressing at a pressure of 20 MPa, it is molded into a desired shape, and the obtained molded body is subjected to CIP treatment (cold isostatic pressing treatment) at a pressure of, for example, 150 MPa. The obtained CIP pressed body is fired by holding it at 900 to 1300 °C for 5 hours in, for example, an air atmosphere to obtain a piezoelectric body composed of a lead-free piezoelectric composition (step T160). As described above, the Young's modulus of the lead-free piezoelectric composition can also be adjusted by the firing temperature in step T160.

[0040] Next, the piezoelectric body obtained in step T160 is cut according to the dimensional accuracy required for the piezoelectric element 10, and the upper and lower surfaces are processed. The size of the piezoelectric element 10 may be appropriately set according to the application in which the piezoelectric element 10 is used. The piezoelectric body thus obtained is subjected to an annealing treatment involving heating to stabilize its properties (step T170). The annealing treatment may be performed in the air, and the annealing temperature is preferably, for example, 300 °C or higher and 800 °C or lower, and more preferably 300 °C or higher and 600 °C or lower. Also, the holding time during the annealing treatment is preferably 3 hours or longer and 20 hours or shorter, and more preferably 5 hours or longer and 10 hours or shorter. By performing such an annealing treatment, the structure of the ceramic such as domains is stabilized, and the change rate of Qm can be further reduced. Thereafter, electrodes are attached to the surface of the piezoelectric body (step T180), and poling treatment is performed (step T190) to complete the piezoelectric element 10.

[0041] Note that the above manufacturing method is just an example, and various other processes and processing conditions for manufacturing the piezoelectric element 10 can be used. For example, instead of separately generating the calcined products of the main phase and the secondary phase in advance and then mixing and firing the powders of both, the raw materials may be mixed and fired in a quantitative ratio according to the composition of the final lead-free piezoelectric composition. However, according to the method of separately generating the calcined products of the main phase and the secondary phase in advance and then mixing them, it is easier to strictly control the compositions of the main phase and the secondary phase, so the yield of the lead-free piezoelectric composition can be increased.

[0042] C. Devices Applied with Piezoelectric Elements: The piezoelectric element 10 can be suitably used in the following devices. Examples of the devices include a ultrasonic scalpel 40, an ultrasonic scaler 50, an ultrasonic cleaner 60, an ultrasonic processing machine 70, a piezoelectric transducer 80, an ultrasonic motor 90, a piezoelectric gyro sensor 100, a piezoelectric filter 110, and a knock sensor 120.

[0043] (C-1) Ultrasonic Scalpel FIG. 3 is a schematic diagram showing an ultrasonic scalpel 40 which is one of the embodiments of the present disclosure. The ultrasonic scalpel 40 includes an ultrasonic vibrator 41 and an operating member 43. The ultrasonic vibrator 41 has the above piezoelectric element 10 and generates ultrasonic vibrations when an electric signal is applied. The ultrasonic vibrator 41 operates to transmit ultrasonic vibrations to the axially configured operating member 43. The ultrasonic vibrator 41 drives the operating member 43 so that an action of incising, peeling or thermocoagulating and hemostasizing biological tissues occurs in the vicinity of the operating member 43.

[0044] (C-2) Ultrasonic Scaler FIG. 4 is a schematic diagram showing an ultrasonic scaler 50 which is one of the embodiments of the present disclosure. The ultrasonic scaler 50 is a dental medical device for crushing and cleaning dental calculus and contaminants adhering to the surface of teeth by ultrasonic vibrations. The ultrasonic scaler 50 includes an ultrasonic vibrator 51 and a dental tip 52. The ultrasonic vibrator 51 has the above piezoelectric element 10 and generates ultrasonic vibrations when an electric signal is applied. The ultrasonic vibrator 51 operates to transmit ultrasonic vibrations to the dental tip 52.

[0045] (C-3) Ultrasonic cleaner FIG. 5 is a schematic diagram showing an ultrasonic cleaner 60 which is one of the embodiments of the present disclosure. The ultrasonic cleaner 60 includes an ultrasonic vibrator 61 and a cleaning container 63. The ultrasonic vibrator 61 has the piezoelectric element 10 and generates ultrasonic vibration when an electric signal is applied. The object to be cleaned 65 is put into the cleaning container 63 containing the cleaning liquid, and the ultrasonic vibration generated by vibrating the ultrasonic vibrator 61 is transmitted to the cleaning liquid, and the object to be cleaned 65 is cleaned.

[0046] (C-4) Ultrasonic processing machine FIG. 6 is a schematic diagram showing an ultrasonic processing machine 70 which is one of the embodiments of the present disclosure. The ultrasonic processing machine 70 includes a base material 71, an ultrasonic vibrator 73, a grindstone part 75, a spindle 77, and a mounting jig 79. The base material 71 is in a disk shape, and a grindstone part 75 is formed on its outer periphery. The center of the base material 71 is fixed to the spindle 77.

[0047] The ultrasonic vibrator 73 has the piezoelectric element 10 and generates ultrasonic vibration when an electric signal is applied. The driving direction of the ultrasonic vibrator 73 is the radial direction from the center of the base material 71 toward the outer periphery. While generating vibration by the ultrasonic vibrator 73, the grindstone part 75 formed on the outer periphery of the base material 71 is pressed against the object to be processed with the spindle 77 rotated about its axis, whereby the object to be processed can be cut.

[0048] (C-5) Piezoelectric transducer FIG. 7 is a schematic diagram showing a piezoelectric transducer 80 which is one of the embodiments of the present disclosure. The piezoelectric transducer 80 is an electromechanical energy conversion device that converts an electric signal into mechanical displacement. The piezoelectric transducer 80 includes a piezoelectric element 81. The piezoelectric element 81 has the same configuration as the piezoelectric element 10. The piezoelectric element 81 has a lead-free piezoelectric member 83 and electrodes 85 and 87 attached to both surfaces of the lead-free piezoelectric member 83.

[0049] (C-6) Ultrasonic Motor FIG. 8 is a schematic diagram showing an ultrasonic motor 90 which is one of the embodiments of the present disclosure. The ultrasonic motor 90 includes an ultrasonic vibrator 91, a rotor 93, and an output shaft 95. The ultrasonic vibrator 91 has the piezoelectric element 10. The ultrasonic motor 90 is an actuator that converts the natural vibration generated by the ultrasonic vibrator 91 into rotational motion of the rotor 93 or the like by frictional force. For example, when an alternating voltage is applied to the piezoelectric element 10, a flexural traveling wave is generated in the ultrasonic vibrator 91, and each point on the sliding surface of the ultrasonic vibrator 91 performs elliptical motion. When the rotor 93 is pressed against the sliding surface of the ultrasonic vibrator 91, the rotor 93 receives frictional force from the ultrasonic vibrator 91 and rotates in the direction opposite to the flexural traveling wave.

[0050] (C-7) Piezoelectric Gyro Sensor FIG. 9 is a schematic diagram showing a piezoelectric gyro sensor 100 which is one of the embodiments of the present disclosure. The piezoelectric gyro sensor 100 is a device that detects an angular velocity by utilizing the Coriolis force generated in the vibrator. The piezoelectric gyro sensor 100 has a piezoelectric element 107 including a lead-free piezoelectric member 101 and electrodes 103 and 105 coated on both surfaces of the lead-free piezoelectric member 101. The piezoelectric element 107 has the same configuration as the piezoelectric element 10.

[0051] (C-8) Piezoelectric Filter FIG. 10 is a schematic diagram showing a laminated piezoelectric filter 110 which is one of the embodiments of the present disclosure. The piezoelectric filter 110 is a device that excites elastic waves and extracts an electrical signal in a specific frequency band. The laminated piezoelectric filter 110 has a cylindrical lead-free piezoelectric member 111 and a piezoelectric element 117 including electrodes 113 and 115 on both surfaces of the lead-free piezoelectric member 111. The piezoelectric element 117 has the same configuration as the piezoelectric element 10.

[0052] (C-9) Knock Sensor FIG. 11 is a schematic diagram of a knock sensor 120 which is one of the embodiments of the present disclosure. The knock sensor 120 is used, for example, by being attached to an engine block, and is a device that converts the force applied by the vibration of the engine block caused by knocking into an electrical signal to detect knocking. The knock sensor 120 has a lead-free piezoelectric member 121 and a piezoelectric element 127 including electrodes 123 and 125. The piezoelectric element 127 has the same configuration as the piezoelectric element 10 described above.

[0053] According to the lead-free piezoelectric composition of the present embodiment configured as described above, by setting the Young's modulus of the lead-free piezoelectric composition including a main phase composed of an alkali niobate perovskite-type oxide and a sub-phase including a metal oxide different from the alkali niobate perovskite-type oxide constituting the main phase to 90 GPa or more, the change rate of the mechanical quality factor Qm between low load and high load (low vibration stress and high vibration stress) can be suppressed. Therefore, the piezoelectric characteristics are stable from low load to high load, and it becomes possible to manufacture a piezoelectric element that performs stable operation with less energy loss during driving.

Examples

[0054] Twelve types of lead-free piezoelectric compositions of samples S1 to S12 having different configurations related to the main phase and the sub-phase were prepared, and an evaluation was performed on the change rate of Qm from low load to high load.

[0055] FIG. 12 is an explanatory diagram collectively showing the configurations and evaluation results of the prepared samples. FIG. 13 is an explanatory diagram showing the configuration of the main phase of each sample. In FIG. 13, the "composition of the calcined powder 1" prepared to form the main phase, the "additive" added to the calcined powder 1, and the composition of the obtained main phase are shown.

[0056] <Preparation of Lead-Free Piezoelectric Composition> [Sample S1] As Sample S1, a lead-free piezoelectric composition was prepared which includes a main phase shown as "main phase A1" in FIG. 13 and a secondary phase including an oxide having a spinel-type structure represented by CoZnTiO4 (see FIG. 12). In FIG. 2, in order to produce the calcined powder constituting the main phase, the process T110 of mixing the raw material powders of the main phase and the process T120 of calcining the mixed raw materials were described. However, when producing the calcined powder constituting the main phase of Sample S1 and Samples S2 to S12 described later, after mixing a part of the raw material powders of the main phase, it was calcined to produce calcined powder 1. Then, the remaining raw material powders were mixed with calcined powder 1 and calcined to produce calcined powder 2 as the calcined powder of the main phase. When producing calcined powder 1, K2CO3 powder, Na2CO3 powder, and Nb2O5 powder were used as the raw material powders and weighed according to the "composition of calcined powder 1" shown in FIG. 13. Ethanol was added to the weighed raw material powders, and wet mixing was performed with a ball mill for 15 hours or more to obtain a slurry. Then, the mixed powder obtained by drying the slurry was calcined at 900 ° C. for 5 hours in an air atmosphere to obtain calcined powder 1.

[0057] Additives having the composition shown as the additives of "main phase A1" in FIG. 13 were added to the obtained calcined powder 1 at the ratio shown in FIG. 13 (2.5 mol% of BaCO3 and 2.5 mol% of ZrO2). Here, the addition amounts of the additives shown for Samples S1 to S12 in FIG. 13 are shown as relative amounts when the calcined powder 1 to which the addition is made is 100 mol%. Then, ethanol was added to the raw material powders to which the additives were added, and wet mixing was performed with a ball mill for 15 hours or more to obtain a slurry. Then, the mixed powder obtained by drying the slurry was calcined at 900 ° C. for 5 hours in an air atmosphere to obtain calcined powder 2 which is the calcined powder of the main phase.

[0058] Separate from the production of the calcined powder 2 of the main phase, a calcined powder of the secondary phase was produced. When producing the calcined powder of the secondary phase, Co3O4 powder, ZnO powder, and TiO2 powder were used as raw material powders and weighed according to the composition of the secondary phase (CoZnTiO4) shown in Fig. 12. Ethanol was added to the weighed raw material powders, and wet mixing was carried out in a ball mill for 15 hours or more to obtain a slurry. Thereafter, the mixed powder obtained by drying the slurry was calcined at 1200 °C for 5 hours in an air atmosphere to obtain a calcined powder of the secondary phase (steps T130 to T140).

[0059] Thereafter, the above-mentioned calcined powder 2 of the main phase and the calcined powder of the secondary phase were each weighed, a binder and ethanol were added, and wet mixing was carried out in a ball mill to obtain a slurry. Thereafter, the obtained slurry was dried, granulated, uniaxially pressed at a pressure of 20 MPa, and formed into a desired shape. Thereafter, CIP treatment (cold isostatic pressing treatment) was carried out at a pressure of 150 MPa to obtain a formed body (step T150). The obtained formed body was fired at 1130 °C for 5 hours in an air atmosphere (step T160) to produce a sample S1, which is a lead-free piezoelectric composition (piezoelectric body) comprising a "main phase A1" and a secondary phase composed of CoZnTiO4, which is a spinel-type oxide. The content ratio (volume %) of the secondary phase in sample S1 and samples S3 to S12 described later was unified at 1.5 volume %.

[0060] [Sample S2] As sample S2, a lead-free piezoelectric composition composed of the main phase shown as "main phase A2-1" in Fig. 13 and not having a secondary phase was produced. The calcined powder 1 for forming the main phase of sample S2 was produced in the same manner as sample S1. Then, additives having the composition shown as the additives of "main phase A2-1" in Fig. 13 were added to the obtained calcined powder 1 at the ratio shown in Fig. 13 (2.5 mol% BaCO3, 2.5 mol% ZrO2, and 0.5 mol% MnO2), and calcined powder 2 was produced under the same conditions as sample S1.

[0061] Thereafter, ethanol and a binder were added to the calcined powder 2, and wet mixing was performed using a ball mill to obtain a slurry. Thereafter, the slurry was dried, granulated, uniaxially pressed at a pressure of 20 MPa, and formed into a desired shape. Thereafter, a CIP treatment was performed at a pressure of 150 MPa to obtain a formed body (corresponding to step T150). The obtained formed body was fired at 1130 °C for 5 hours in an air atmosphere (corresponding to step T160) to produce a lead-free piezoelectric composition (piezoelectric body) of sample S2.

[0062] [Sample S3] As sample S3, a lead-free piezoelectric composition was prepared that includes a main phase shown as "main phase B1" in FIG. 13 and a secondary phase containing an oxide having a tungsten bronze structure represented by Ba2KNb5O 15 (see FIG. 12). Sample S3 was prepared in the same manner as the calcined powder 1 of sample S1, except that the mixing ratios of the raw material powders, K2CO3 powder, Na2CO3 powder, and Nb2O5 powder, were made different from those of sample S1 as shown in "Composition of calcined powder 1" in FIG. 13 when preparing the calcined powder 1. Also, the conditions for adding additives to the calcined powder 1 to prepare the calcined powder 2 were the same as those of sample S1.

[0063] When preparing the calcined powder of the secondary phase, BaCO3 powder, K2CO3 powder, and Nb2O5 powder were used as raw material powders and weighed according to the composition of the secondary phase (Ba2KNb5O 15 ) shown in FIG. 12. Ethanol was added to the weighed raw material powders, and wet mixing was performed using a ball mill for 15 hours or more to obtain a slurry. Thereafter, the mixed powder obtained by drying the slurry was calcined at 1200 °C for 5 hours in an air atmosphere to obtain a calcined powder of the secondary phase (steps T130 to T140). The production of the lead-free piezoelectric composition (piezoelectric body) using the calcined powder 2 of the main phase and the calcined powder of the secondary phase was performed in the same manner as that of sample S1.

[0064] [Samples S4 to S9] Samples S4 to S9 were prepared in the same manner as Sample S1, except that the type and ratio of the additives added to the calcined powder 1 were varied so as to include the main phase shown in Fig. 13. Also, Samples S4, S5, S7 to S9 used the same calcined powder for the secondary phase as Sample S3, and Sample S6 used the same calcined powder as Sample S1. The lead-free piezoelectric composition (piezoelectric body) was prepared using the calcined powder 2 for the main phase and the calcined powder for the secondary phase in the same manner as Sample S1.

[0065] [Samples S10 to S11] Samples S10 to S11 were prepared using the same calcined powder 2 for the main phase and the same calcined powder for the secondary phase as Sample S7, and have the same composition, but the firing temperatures in step T160 were varied. The firing temperatures were 1130°C for Sample S7, 1100°C for Sample S10, 1120°C for Sample S11, and 1140°C for Sample S12. The manufacturing conditions other than the firing temperature for Samples S10 to S11 were the same as those for Sample S7.

[0066] <Method for Measuring Young's Modulus> The Young's modulus of each sample was measured by an elastic modulus test using the ultrasonic pulse method specified in JIS R 1602. That is, the dynamic elastic modulus was measured based on the velocity when an ultrasonic pulse propagated through the test piece. Specifically, for the mirror-polished sample, using a longitudinal wave oscillator and a transverse wave oscillator, the longitudinal wave velocity V I (unit: m / s) and the transverse wave velocity V S (unit: m / s) were measured. For the measurement, an ultrasonic high-precision thickness gauge MODEL25L manufactured by Nihon Panametrix Co., Ltd. was used. The elastic modulus (Young's modulus) was calculated from the measured values by the following equation (7). In equation (7), ρ is the density of the sample (unit: kg / m 3) ). The Archimedes method was used to measure the density. Here, the density represents the bulk density, and the bulk density was determined from the mass of the sample measured in air and the mass of the sample measured in a liquid.

[0067]

Equation

[0068] <Method for Evaluating Lead-Free Piezoelectric Composition> The lead-free piezoelectric composition was evaluated based on the change rate of the mechanical quality factor Qm. The measurement of the mechanical quality factor Qm at each load was performed by the electrical transient response method. The electrical transient response method is a well-known method for calculating piezoelectric characteristics at high vibrations from the decay waveform immediately after the application of a pulse voltage. In this example, for each sample processed into a 31 shape (strip shape, 1 mm × 3 mm × 12 mm), with the device configuration of a function generator (33500B), a bipolar amplifier (HAS 4052), a laser Doppler vibrometer (NLV-2500), and an oscilloscope (DLM3034), a burst wave of the resonance frequency of each sample existing between 100 kHz and 300 kHz was applied at 100 V, and the decay waveforms of the vibration velocity and current immediately after the voltage application were obtained. Using the obtained measurement data, the mechanical quality factor Qm and the vibration stress Tm were calculated by the following equations (8) to (10), respectively.

[0069]

Equation

Equation

Equation

[0070] Here, f r is the instantaneous frequency of the vibration velocity, V is the instantaneous amplitude of the vibration velocity, β is the decay coefficient, Qm is the mechanical quality factor, s 11 EElastic compliance is represented by, ρ is the density of the sample, X is the length of the sample, and Tm indicates the amplitude (load) of the maximum stress at the equivalent center of the sample. When Tm = 1 MPa is defined as a low load and Tm = 20 MPa is defined as a high load, the rate of change of Qm was calculated using the value of Qm at Tm = 1 MPa and the value of Qm at Tm = 20 MPa. The "rate of change of Qm" was defined as the ratio (unit: %) of "the difference between the value of Qm at Tm = 1 MPa and the value of Qm at Tm = 20 MPa" to "the value of Qm at Tm = 1 MPa". In Fig. 12, those with a rate of change of the mechanical quality factor Qm of 40% or less were evaluated as good products and indicated as "○", and those with a rate of change of Qm exceeding 40% were indicated as "×".

[0071] As shown in Fig. 12, by setting the Young's modulus of the lead-free piezoelectric composition to 90 GPa or more, it was confirmed that the rate of change of the mechanical quality factor Qm between low load and high load (low vibration stress and high vibration stress) can be suppressed (it can be made 40% or less in the examples). At this time, the Young's modulus of the lead-free piezoelectric composition may be adjusted by, for example, the composition of the main phase, secondary phase, etc. (see Samples S1, S3 to S9), or may be adjusted by manufacturing conditions such as the firing temperature during manufacturing (see Samples S7, S10 to S12). It was confirmed that if the Young's modulus can be made 90 GPa or more, the rate of change of Qm can be suppressed.

[0072] The present disclosure is not limited to the above-described embodiments and the like, and can be realized in various configurations without departing from the gist thereof. For example, the technical features in the embodiments corresponding to the technical features in each form described in the summary of the invention can be appropriately replaced or combined in order to solve some or all of the above-described problems or to achieve some or all of the above-described effects. Further, if the technical feature is not described as essential in this specification, it can be appropriately deleted.

[0073] The present disclosure can also be realized in the following forms. [Application Example 1] A lead-free piezoelectric composition, A main phase composed of an alkali niobate perovskite-type oxide, and a secondary phase containing a metal oxide different from the alkali niobate perovskite-type oxide constituting the main phase, comprising, characterized in that the Young's modulus is 90 GPa or more lead-free piezoelectric composition. [Application Example 2] The lead-free piezoelectric composition according to Application Example 1, characterized in that the Young's modulus is 100 GPa or more lead-free piezoelectric composition. [Application Example 3] The lead-free piezoelectric composition according to Application Example 1 or 2, characterized in that the Young's modulus is 105 GPa or more lead-free piezoelectric composition. [Application Example 4] The lead-free piezoelectric composition according to any one of Application Examples 1 to 3, characterized in that the metal oxide constituting the secondary phase contains at least one of a metal oxide having a spinel structure and a metal oxide having a tungsten bronze structure lead-free piezoelectric composition. [Application Example 5] The lead-free piezoelectric composition according to any one of Application Examples 1 to 4, wherein the alkali niobate perovskite-type oxide constituting the main phase has a composition formula (A1 a M1 b ) c (Nb d1 M2 d2 M3 d3 )O 3+e(However, element A1 is at least one of alkali metals, element M1 is at least one of Ba, Ca, and Sr, element M2 is at least one of Ti, Zr, Ta, Hf, Sn, Sb, and Si, element M3 is at least one of Mn, Mg, Al, Sc, Fe, Co, Ni, Zn, Ga, and Y, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, d1 + d2 + d3 = 1, and e represents a value indicating oxygen deficiency or excess), characterized in that it is an alkali niobate perovskite-type oxide Lead-free piezoelectric composition. [Application Example 6] The lead-free piezoelectric composition according to Application Example 5, wherein element A1 is at least one of K and Na, element M2 is at least one of Ti and Zr, element M3 is Mn, characterized in that 0 < a ≤ 1 Lead-free piezoelectric composition. [Application Example 7] A piezoelectric body formed of the lead-free piezoelectric composition according to any one of Application Examples 1 to 6, and electrodes attached to the piezoelectric body, characterized in that it comprises a piezoelectric element. [Application Example 8] An apparatus characterized by comprising the piezoelectric element according to Application Example 7. [Application Example 9] The apparatus according to Application Example 8, wherein the apparatus is any one of a ultrasonic scalpel, a ultrasonic scaler, a ultrasonic cleaner, a ultrasonic processing machine, a piezoelectric transducer, a ultrasonic motor, a piezoelectric gyro sensor, a piezoelectric filter, and a knock sensor.

Description of Reference Numerals

[0074] 10... Piezoelectric element 20... Piezoelectric body 31, 32... Electrodes 40... Ultrasonic scalpel 41... Ultrasonic oscillator 43…Actuating member 50…Ultrasonic scaler 51…Ultrasonic vibrator 52…Dental tip 60…Ultrasonic cleaner 61…Ultrasonic vibrator 63…Cleaning container 65…Object to be cleaned 70…Ultrasonic processing machine 71…Base material 73…Ultrasonic vibrator 75…Grinding wheel part 77…Spindle 79…Mounting jig 80…Piezoelectric transducer 81…Piezoelectric element 83…Lead-free piezoelectric member 85…Electrode 90…Ultrasonic motor 91…Ultrasonic vibrator 93…Rotor 95…Output shaft 100…Piezoelectric gyro sensor 101…Lead-free piezoelectric member 103…Electrode 107…Piezoelectric element 110…Piezoelectric filter 111…Lead-free piezoelectric member 113…Electrode 117…Piezoelectric element 120…Knock sensor 121…Lead-free piezoelectric member 123…Electrode 127…Piezoelectric element

Claims

1. A lead-free piezoelectric composition comprising: A main phase composed of an alkali niobate-based perovskite-type oxide; and A secondary phase containing a metal oxide different from the alkali niobate-based perovskite-type oxide constituting the main phase, and having a Young's modulus of 90 GPa or more. Lead-free piezoelectric composition.

2. The lead-free piezoelectric composition according to claim 1, having a Young's modulus of 100 GPa or more. Lead-free piezoelectric composition.

3. The lead-free piezoelectric composition according to claim 1, having a Young's modulus of 105 GPa or more. Lead-free piezoelectric composition.

4. The lead-free piezoelectric composition according to claim 1, wherein the metal oxide constituting the secondary phase contains at least one of a metal oxide having a spinel-type structure and a metal oxide having a tungsten bronze-type structure. Lead-free piezoelectric composition.

5. The lead-free piezoelectric composition according to claim 1, wherein the alkali niobate-based perovskite-type oxide constituting the main phase has a composition formula (A1 ａ M1 ｂ ) ｃ (Nb ｄ１ M2 ｄ２ M3 ｄ３ )O ３＋ｅ(However, element A1 is at least one of alkali metals, element M1 is at least one of Ba, Ca, and Sr, element M2 is at least one of Ti, Zr, Ta, Hf, Sn, Sb, and Si, element M3 is at least one of Mn, Mg, Al, Sc, Fe, Co, Ni, Zn, Ga, and Y, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, d1 + d2 + d3 = 1, and e represents a value of oxygen deficiency or excess), and it is characterized by being an alkali niobate perovskite-type oxide. Lead-free piezoelectric composition.

6. The lead-free piezoelectric composition according to claim 5, wherein the element A1 is at least one of K and Na, the element M2 is at least one of Ti and Zr, the element M3 is Mn, and 0 < a ≦ 1, and it is characterized by Lead-free piezoelectric composition.

7. A piezoelectric body formed of the lead-free piezoelectric composition according to any one of claims 1 to 6, and an electrode attached to the piezoelectric body, and A piezoelectric element characterized by comprising the above.

8. An apparatus characterized by comprising the piezoelectric element according to claim 7.

9. The apparatus according to claim 8, wherein the apparatus is any one of an ultrasonic scalpel, an ultrasonic scaler, an ultrasonic cleaner, an ultrasonic processing machine, a piezoelectric transducer, an ultrasonic motor, a piezoelectric gyro sensor, a piezoelectric filter, and a knock sensor.

Images