Lead-free piezoelectric composition, piezoelectric element, and device

Abstract

This lead-free piezoelectric composition has a primary phase formed from an alkali niobate-based perovskite-type oxide and a secondary phase comprising a metal oxide that is different from the alkali niobate-based perovskite-type oxide which forms the primary phase. The composition has a Young's modulus of at least 90 GPa.

Description

Lead-free piezoelectric compositions, piezoelectric elements, and devices

[0001] The present disclosure relates to lead-free piezoelectric compositions, piezoelectric elements, and devices.

[0002] Conventionally, PZT (lead zirconate titanate) compositions have been widely used as compositions exhibiting piezoelectricity, but there is a demand for the development of lead-free piezoelectric compositions that do not use lead in order to reduce environmental impact, etc. As a candidate for such lead-free piezoelectric compositions, for example, alkali niobate perovskite oxides have been proposed. Specifically, Patent Documents 1 and 2 disclose K ｘ Na （１－ｘ） NbO ３ The publication discloses a configuration in which piezoelectric properties such as the mechanical quality factor Qm are improved by specifying the composition of a piezoelectric material (KNN-based piezoelectric material) containing as a main component a compound represented by the formula: The mechanical quality factor Qm is a parameter that represents the sharpness of mechanical vibration (sharpness of the resonance spectrum) near the resonance frequency when the piezoelectric composition generates a natural vibration, and the larger the mechanical quality factor Qm, the lower the loss, and the more efficient the actuator including the piezoelectric composition can be.

[0003] Patent No. 6326198 Patent No. 4929522

[0004] Further improvements in piezoelectric properties are required for such lead-free piezoelectric compositions, and it is desirable to have a smaller rate of change in the mechanical quality factor Qm from low load to high load (from low vibration stress to high vibration stress). In other words, since Qm generally decreases as the load increases, it is desirable to minimize the decrease in Qm as the load increases, particularly in applications requiring operation under high load. However, in alkali niobate perovskite oxides, a configuration for suppressing the rate of change in the mechanical quality factor Qm between low and high loads has not been fully investigated.

[0005] The present disclosure can be realized in the following embodiments. [1] According to one embodiment of the present disclosure, a lead-free piezoelectric composition is provided. The lead-free piezoelectric composition comprises a main phase made of an alkali niobate perovskite oxide and a subphase containing a metal oxide different from the alkali niobate perovskite oxide constituting the main phase, and has a Young's modulus of 90 GPa or more. According to this embodiment, the lead-free piezoelectric composition, which comprises a main phase made of an alkali niobate perovskite oxide and a subphase containing a metal oxide different from the alkali niobate perovskite oxide constituting the main phase, has a Young's modulus of 90 GPa or more. By setting the Young's modulus of the lead-free piezoelectric composition to 90 GPa or more, the rate of change in the mechanical quality factor Qm between low and high loads (low vibration stress and high vibration stress) can be suppressed. This makes it possible to obtain a piezoelectric element with stable piezoelectric characteristics from low to high loads. [2] The lead-free piezoelectric composition of the above embodiment may have a Young's modulus of 100 GPa or more. This configuration further enhances the effect of suppressing the rate of change in the mechanical quality factor Qm. [3] In the lead-free piezoelectric composition of the above embodiment, 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 embodiment, the metal oxide constituting the subphase may include at least one of a metal oxide having a spinel structure and a metal oxide having a tungsten bronze 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 embodiment, the alkali niobate perovskite oxide constituting the main phase is a niobate-based perovskite oxide represented by the composition formula (A1 ａ M1 ｂ ) ｃ (Nb ｄ１ M2 ｄ２ M3 ｄ３ ) O ３＋ｅ(wherein element A1 is at least one alkali metal, 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). With this configuration, the mechanical quality factor Qm of the lead-free piezoelectric composition can be increased. [6] In the lead-free piezoelectric composition of the above embodiment, the element A1 may be at least one of K and Na, the element M2 may be at least one of Ti and Zr, and the element M3 may be Mn, with 0<a≦1. This configuration facilitates improving the piezoelectric properties of the lead-free piezoelectric composition. [7] According to another embodiment of the present disclosure, there is provided a piezoelectric element comprising a piezoelectric body formed from the lead-free piezoelectric composition of any one of [1] to [6] and electrodes attached to the piezoelectric body. The piezoelectric element of this embodiment can stabilize the piezoelectric properties of the piezoelectric element from low loads to high loads. This reduces energy loss during driving under high loads, allowing for stable driving. [8] According to yet another embodiment of the present disclosure, there is provided a device comprising the piezoelectric element of [7]. The device of this embodiment includes a piezoelectric element comprising a lead-free piezoelectric composition with stable piezoelectric properties from low loads to high loads, thereby improving the performance of the entire device. The present disclosure can be realized in various forms, for example, a lead-free piezoelectric composition, a piezoelectric element using the same, various devices including a 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.

[0006] 1 is a perspective view showing the appearance of a piezoelectric element; 2 is a flowchart showing an example of a method for manufacturing a piezoelectric element; 3 is a schematic view showing an ultrasonic scalpel as an example of an apparatus; 4 is a schematic view showing an ultrasonic scaler as an example of an apparatus; 5 is a schematic view showing an ultrasonic cleaner as an example of an apparatus; 6 is a schematic view showing an ultrasonic processing machine as an example of an apparatus; 7 is a schematic view showing a piezoelectric transducer as an example of an apparatus; 8 is a schematic view showing an ultrasonic motor as an example of an apparatus; 9 is a schematic view showing a piezoelectric gyro sensor as an example of an apparatus; 10 is a schematic view showing a laminated piezoelectric filter as an example of an apparatus; 11 is a schematic view showing a knock sensor as an example of an apparatus; 12 is an explanatory view showing the configuration and evaluation results of each sample together; 13 is an explanatory view showing the configuration of the main phase of each sample.

[0007] A. Lead-free piezoelectric composition: The lead-free piezoelectric composition of this embodiment comprises a main phase made of an alkali niobate perovskite oxide and a subphase containing a metal oxide different from the alkali niobate perovskite oxide constituting the main phase. 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 perovskite oxide constituting the main phase preferably contains at least one alkali metal (potassium (K), sodium (Na), lithium (Li), etc.) as the alkali component, and particularly preferably contains at least one of potassium (K) and sodium (Na). The alkali niobate perovskite oxide constituting the main phase may also contain an alkaline earth metal (at least one of calcium (Ca), strontium (Sr), barium (Ba), etc.) as the alkali component.

[0009] The alkali niobate perovskite oxide constituting the main phase may contain manganese (Mn). It is believed that manganese (Mn) dissolves as an acceptor in the niobium site (B site of the perovskite crystal structure) to improve the mechanical quality factor Qm. However, manganese (Mn) is not essential.

[0010] The alkali niobate perovskite oxide constituting the main phase is preferably an alkali niobate perovskite oxide that satisfies the following composition formula (1):

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

[0012] In the formula, the element A1 is at least one alkali metal, the element M1 is at least one of Ba, Ca, and Sr, the element M2 is at least one of Ti, Zr, Ta, Hf, Sn, Sb, and Si, the 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, and d1+d2+d3=1, and e is a value indicating an oxygen deficiency or excess.

[0013] In the composition formula (1), the elements A1 and M1 are located at the A site of the perovskite structure, and Nb (niobium), M2, and M3 are located at the B site. The values ​​of the coefficients a, b, d1 to d3, and e in the composition formula (1) are selected from the aforementioned ranges, among the combinations of values ​​that establish the perovskite structure, and are preferred in terms of the electrical and piezoelectric properties of the lead-free piezoelectric composition. In the alkali niobate perovskite oxide shown in the composition formula (1), d1 = 0 (a composition that does not contain Nb) is excluded. The alkali niobate perovskite oxide shown in the composition formula (1) also contains at least one of the elements M2 and M3.

[0014] In the oxygen coefficient (3+e), the coefficient e is a positive or negative value indicating a deficiency or excess of oxygen, with the oxygen coefficient usually being 3. The oxygen coefficient (3+e) can take a value where the main phase constitutes a perovskite oxide. A typical value for the coefficient e is e=0, and -0.1≦e≦0.1 is preferred. The value of the coefficient e can be calculated from the electrical neutrality condition of the composition of the main phase. However, a composition that slightly deviates from the electrical neutrality condition is also acceptable for the composition of the main phase.

[0015] In the above composition formula (1), the element A1 may be at least one of K and Na, the element M2 may be at least one of Ti and Zr, and the element M3 may be Mn, with 0<a≦1. This configuration facilitates improving the piezoelectric properties of the lead-free piezoelectric composition. Such an alkali niobate perovskite oxide can be expressed by the following composition 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] In the formula, a1+a2=a, b1+b2+b3=b, and d2x+d2y=d2. 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, with -0.1≦e≦0.1 being preferred.

[0018] In this case, it is particularly desirable that the values ​​of 0<a1<1 and 0<a2<1 be satisfied for the element A1, 0≦b1≦0.2, 0≦b2≦0.2, and 0≦b3≦0.2 be satisfied for the element M1, 0≦d2x≦0.2 and 0≦d2y≦0.2 be satisfied for the element M2, and 0≦d3≦0.1 be satisfied for the element Mn. This can further improve the piezoelectric properties of the lead-free piezoelectric composition. It is also more desirable that the values ​​of 0<a1≦0.7 and 0.3≦a2<1 be satisfied for the element A1, 0≦b1≦0.1, 0≦b2≦0.1, and 0≦b3≦0.1 be satisfied for the element M1, 0≦d2x≦0.1 and 0≦d2y≦0.1 be satisfied for the element M2, and 0≦d3≦0.08 be satisfied for the element Mn. This can further improve the piezoelectric properties of the lead-free piezoelectric composition.

[0019] (A-2) Regarding the Subphase: The metal oxide constituting the subphase is a metal oxide different from the alkali niobate perovskite oxide constituting the main phase. The presence of such a subphase can improve, for example, the sinterability of the lead-free piezoelectric composition. Furthermore, the presence of the subphase in the main phase can stabilize the crystal structure of the main phase and improve the piezoelectric properties. Furthermore, the subphase can suppress the occurrence of a sudden change in properties due to the existence of a phase transition point between −50°C and +150°C in the lead-free piezoelectric composition. The subphase may contain one type of metal oxide or multiple types of metal oxides as the metal oxide different from the alkali niobate perovskite oxide. Furthermore, the subphase may contain a crystal phase different from the crystal phase of the above-mentioned metal oxide, and may contain impurity elements.

[0020] The metal oxide constituting such a subphase can be, for example, at least one of a metal oxide having a spinel structure and a metal oxide having a tungsten bronze structure. In addition to or instead of the above metal oxides, the metal oxide constituting the subphase can be, for example, A ２ B ６ O １３The element may be at least one of a Ti-based compound (wherein element A is a monovalent metal and element B is a divalent to hexavalent metal) and an A-Ti-B-O based compound (wherein element A is an alkali metal and element B is at least one of Nb and Ta).

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

[0022] M ｘ TiO ｙ … (3)

[0023] In the formula (3), the element M is a monovalent to tetravalent metal element, 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), and hafnium (Hf). When the element M contains Li, it is preferable that one or more metal elements other than Li be included together with Li in order for the compound of formula (3) to form a spinel crystal structure. The coefficients x and y are relative values ​​when the Ti content is taken as 1. In order for the compound of formula (3) to form a spinel compound, it is preferable that the coefficient x satisfy the relationship 0.5≦x≦5.0. The coefficient y can be any value that forms a spinel compound, but typically it is preferable that the coefficient y satisfy the relationship 2≦y≦8. The coefficients x and y may deviate from the above-mentioned standard values ​​as long as the spinel crystal structure can be maintained and the change in the properties of the compound is within an acceptable range. From the viewpoint of piezoelectric properties, the compound of formula (3) is a compound of the composition formula M containing two divalent metal elements M. ２ TiO ４ or a compound containing two kinds of metal elements M, (M1, M2) TiO ４It is preferable that the compound is represented by the following formula:

[0024] The compound having a tungsten bronze structure is a compound represented by the following formula (4):

[0025] A ｈ B ｉ O １５＋δ … (4)

[0026] In the formula (4), element A includes two or more monovalent or divalent elements, and element B includes one or more divalent to pentavalent elements. Element A is preferably at least one of sodium (Na), potassium (K), lithium (Li), barium (Ba), calcium (Ca), and strontium (Sr). Element B is preferably at least one of niobium (Nb), manganese (Mn), iron (Fe), nickel (Ni), cobalt (Co), zinc (Zr), and zirconium (Zr). Standard values ​​for h, i, and δ are h = 3, i = 5, and δ = 0, respectively. However, as long as the tungsten bronze crystal structure can be maintained and the change in the properties of the compound is within an acceptable range, deviations from the standard values ​​are permissible, and impurity elements may also be included. Specific examples of compounds represented by the formula (4) include those in which element B is preferably Nb, and examples thereof include Ba. ２ KNb ５ O １５ , Ba ２ NaNb ５ O １５ , Ca ２ KNb ５ O １５ , Ca ２ NaNb ５ O １５ The following can be mentioned:

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

[0028] As the A-Ti-B-O based compound, compounds having a composition represented by the following formula (5) or (6) can be used.

[0029] A １－ｘ Ti １－ｘ B １＋ｘ O ５ … (5) A １ Ti ３ B １ O ９ … (6)

[0030] Here, element A is at least one of alkali metals (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) can be any 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 crystalline phase can be obtained.

[0031] Metal oxides such as oxides having a spinel structure and compounds having a tungsten bronze structure that constitute the subphase generally do not have piezoelectric properties. However, their presence in a main phase composed of an alkali niobate perovskite oxide can improve the sinterability of the piezoelectric composition. To ensure the effect of improving the sinterability of the lead-free piezoelectric composition, the content of the subphase is preferably 0.3 vol% or more, and more preferably 0.5 vol% or more. To ensure the piezoelectric properties of the lead-free piezoelectric composition, the content of the subphase is preferably 10 vol% or less, and more preferably 7 vol% or less. The type of compound that constitutes the subphase, such as whether the subphase is a metal oxide having a spinel structure or a metal oxide having a tungsten bronze structure, can be determined by Rietveld analysis using the diffraction results of powder X-ray diffraction (XRD).

[0032] (A-3) Young's Modulus: As described above, the lead-free piezoelectric composition of this embodiment has a Young's modulus of 90 GPa or more. By setting the Young's modulus within the above range, the rate of change in the mechanical quality factor Qm between low and high loads (low vibration stress and high vibration stress) can be suppressed in the lead-free piezoelectric composition. The rate of change in the mechanical quality factor Qm between low and high loads can be calculated and evaluated, for example, by defining a vibration stress Tm = 1 MPa as a low load and a vibration stress Tm = 20 MPa as a high load, using the Qm value when Tm = 1 MPa and the Qm value when Tm = 20 MPa. The reason for the effect of suppressing the rate of change in the mechanical quality factor Qm is thought to be that setting the Young's modulus within the above range ensures the hardness of the lead-free piezoelectric composition, thereby stabilizing the structure of the ceramic constituting the lead-free piezoelectric composition, specifically the domain structure within the particles. From the viewpoint of obtaining the above-mentioned effect by increasing the Young's modulus of the lead-free piezoelectric composition and ensuring 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, if the Young's modulus of the lead-free piezoelectric composition becomes large and the lead-free piezoelectric composition becomes excessively hard, the lead-free piezoelectric composition becomes difficult to vibrate, which may result in a decrease in the piezoelectric performance of a piezoelectric element including the lead-free piezoelectric composition. Therefore, from the viewpoint of suppressing the decrease in the piezoelectric performance, the Young's modulus of the lead-free piezoelectric composition is, for example, preferably 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 subphase that make up the lead-free piezoelectric composition, particularly the composition of the main phase that is contained in a higher proportion in the lead-free piezoelectric composition. The Young's modulus of the lead-free piezoelectric composition can also 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.

[0035] B. Piezoelectric Element: (B-1) Configuration of Piezoelectric Element: Fig. 1 is a perspective view showing the appearance of a piezoelectric element 10 according to this embodiment. This piezoelectric element 10 includes a piezoelectric body 20 formed from the lead-free piezoelectric composition of this 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 and lower surfaces of the disc-shaped piezoelectric body 20. Note that piezoelectric elements of 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 a manufacturing method of the piezoelectric element 10. When manufacturing the piezoelectric element 10, first, raw materials for the main phase of the lead-free piezoelectric composition are mixed (step T110). Here, the raw materials necessary for the main phase raw material powder are selected and weighed to obtain the target composition. The raw material powder can be an oxide, carbonate, or hydroxide of each element contained in the alkali niobate perovskite oxide that constitutes the main phase. Specifically, K ２ CO ３ Powder, Na ２ CO ３ Powder, Li ２ CO ３ powder, CaCO ３Powder, SrCO ３ Powder, BaCO ３ powder, Nb ２ O ５ Powder, TiO ２ Powder, ZrO ２ In step T110, ethanol is added to the raw material powder, 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, in air at 600 to 1000°C 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 raw material mixing in step T110 and calcination in step T120, but a different configuration may be used. For example, the raw material powders may be mixed and fired multiple times. Specifically, first, raw material powders containing multiple elements that are some of the elements contained in the target alkali niobate perovskite oxide 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 to obtain calcined powder 2. In this manner, the calcined powder of the main phase may be produced.

[0038] Separately from the above-described step T110, raw materials for the subphase of the lead-free piezoelectric composition are mixed (step T130). Here, the raw materials necessary for the subphase are selected and weighed to obtain the target composition. The raw material powders can be oxides, carbonates, or hydroxides of the elements contained in the metal oxides that form the subphase, such as oxides having a spinel structure or oxides having a tungsten bronze structure. Specifically, BaCO ３ powder, CO ３ Powder, SrCO ３ Powder, Na ２ CO ３ powder, K ２ CO ３ powder, Nb ２ O ５ Powder, Co ３ O ４ powder, ZnO powder, TiO ２Raw material powders are selected as needed from powders and other materials and weighed. Ethanol is then added to these raw material powders, and they are wet-mixed in a ball mill to obtain a slurry. 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 (step T140).

[0039] The calcined powder of the main phase obtained in step T120 and the calcined powder of the subphase obtained in step T140 are then weighed, and a binder and ethanol are added. The mixture is then wet-mixed in a ball mill to obtain a slurry. The resulting slurry is then dried, granulated, and molded (step T150). Specifically, the mixture is molded into a desired shape, for example, by uniaxial pressing at a pressure of 20 MPa. The resulting molded body is then subjected to cold isostatic pressing (CIP) at a pressure of 150 MPa, for example. The resulting CIP-pressed body is then sintered, for example, at 900 to 1300°C in air for 5 hours, to obtain a piezoelectric body composed of the lead-free piezoelectric composition (step T160). As previously mentioned, the Young's modulus of the lead-free piezoelectric composition can also be adjusted by the sintering 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 top and bottom surfaces are processed. The size of the piezoelectric element 10 can be appropriately determined depending on the application for which the piezoelectric element 10 is to be used. The piezoelectric body thus obtained is subjected to an annealing treatment involving heating to stabilize its characteristics (step T170). The annealing treatment may be performed in the atmosphere, and the annealing temperature is preferably, for example, 300°C to 800°C, and more preferably 300°C to 600°C. Furthermore, the holding time during the annealing treatment is preferably 3 hours to 20 hours, and more preferably 5 hours to 10 hours. Such an annealing treatment stabilizes the ceramic structure, such as domains, and further reduces the rate of change in Qm. Subsequently, electrodes are attached to the surface of the piezoelectric body (step T180), and a polarization treatment is performed (step T190), completing the piezoelectric element 10.

[0041] The above-described manufacturing method is merely an example, and various other steps and processing conditions can be used to manufacture the piezoelectric element 10. 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 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 precisely controlled, which can increase the yield of the lead-free piezoelectric composition.

[0042] C. Devices using the piezoelectric element: The piezoelectric element 10 can be suitably used in the following devices, such as an 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 according to one embodiment of the present disclosure. The ultrasonic scalpel 40 includes an ultrasonic vibrator 41 and an operating member 43. The ultrasonic vibrator 41 has the piezoelectric element 10 and is driven to generate ultrasonic vibrations when an electrical signal is applied. The ultrasonic vibrator 41 operates to transmit ultrasonic vibrations to the operating member 43, which is configured in a shaft shape. The ultrasonic vibrator 41 drives the operating member 43 so as to perform an incision, ablation, or thermal coagulation hemostasis on biological tissue in the vicinity of the operating member 43.

[0044] (C-2) Ultrasonic Scaler FIG. 4 is a schematic diagram showing an ultrasonic scaler 50 according to one embodiment of the present disclosure. The ultrasonic scaler 50 is a dental medical device for breaking down and cleaning tartar and other contaminants adhering to the surface of teeth using ultrasonic vibrations. The ultrasonic scaler 50 includes an ultrasonic vibrator 51 and a dental tip 52. The ultrasonic vibrator 51 has the piezoelectric element 10 and is driven to generate ultrasonic vibrations when an electrical signal is applied. The ultrasonic vibrator 51 operates to transmit the ultrasonic vibrations to the dental tip 52.

[0045] (C-3) Ultrasonic Cleaner Figure 5 is a schematic diagram showing an ultrasonic cleaner 60 according to one embodiment 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 is driven to generate ultrasonic vibrations when an electrical signal is applied. An object 65 to be cleaned is placed in the cleaning container 63 containing a cleaning solution, and the ultrasonic vibrator 61 is vibrated to generate ultrasonic vibrations, which are transmitted to the cleaning solution, thereby cleaning the object 65 to be cleaned.

[0046] (C-4) Ultrasonic Processing Machine Figure 6 is a schematic diagram showing an ultrasonic processing machine 70 according to one embodiment of the present disclosure. The ultrasonic processing machine 70 includes a substrate 71, an ultrasonic vibrator 73, a grinding stone 75, a spindle 77, and a mounting jig 79. The substrate 71 is disk-shaped, and the grinding stone 75 is formed on its outer periphery. The center of the substrate 71 is fixed to the spindle 77.

[0047] The ultrasonic vibrator 73 has the piezoelectric element 10 and is driven to generate ultrasonic vibrations when an electric signal is applied. The driving direction of the ultrasonic vibrator 73 is a radial direction from the center of the substrate 71 to the periphery. While the ultrasonic vibrator 73 generates vibrations, the spindle 77 is rotated about its axis, and the grinding stone portion 75 formed on the periphery of the substrate 71 is pressed against the workpiece, thereby cutting the workpiece.

[0048] (C-5) Piezoelectric Transducer Fig. 7 is a schematic diagram showing a piezoelectric transducer 80 according to one embodiment of the present disclosure. The piezoelectric transducer 80 is an electromechanical energy conversion device that converts an electrical signal into a mechanical displacement. The piezoelectric transducer 80 includes a piezoelectric element 81. The piezoelectric element 81 has a configuration similar to that of the piezoelectric element 10 described above. The piezoelectric element 81 includes a lead-free piezoelectric member 83 and electrodes 85 and 87 attached to both sides of the lead-free piezoelectric member 83.

[0049] (C-6) Ultrasonic Motor FIG. 8 is a schematic diagram showing an ultrasonic motor 90 according to one embodiment 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 includes the piezoelectric element 10. The ultrasonic motor 90 is an actuator that converts the natural vibration generated in the ultrasonic vibrator 91 into rotational motion of the rotor 93 by frictional force. For example, when an AC voltage is applied to the piezoelectric element 10, a bending traveling wave is generated in the ultrasonic vibrator 91, and each point on the sliding surface of the ultrasonic vibrator 91 moves elliptically. When the rotor 93 is pressed against the sliding surface of the ultrasonic vibrator 91, the rotor 93 receives a frictional force from the ultrasonic vibrator 91 and rotates in the opposite direction to the bending traveling wave.

[0050] (C-7) Piezoelectric Gyro Sensor Fig. 9 is a schematic diagram showing a piezoelectric gyro sensor 100 according to an embodiment of the present disclosure. The piezoelectric gyro sensor 100 is a device that detects angular velocity by utilizing the Coriolis force generated in a vibrator. The piezoelectric gyro sensor 100 includes a lead-free piezoelectric member 101 and a piezoelectric element 107 that includes electrodes 103 and 105 applied to both sides of the lead-free piezoelectric member 101. The piezoelectric element 107 has the same configuration as the piezoelectric element 10 described above.

[0051] (C-8) Piezoelectric Filter Fig. 10 is a schematic diagram showing a laminated piezoelectric filter 110 according to one embodiment of the present disclosure. The piezoelectric filter 110 is a device that excites elastic waves to extract an electrical signal in a specific frequency band. The laminated piezoelectric filter 110 includes a cylindrical lead-free piezoelectric member 111 and a piezoelectric element 117 having electrodes 113 and 115 on both sides of the lead-free piezoelectric member 111. The piezoelectric element 117 has a configuration similar to that of the piezoelectric element 10.

[0052] (C-9) Knock Sensor FIG. 11 is a schematic diagram of a knock sensor 120 according to an embodiment of the present disclosure. The knock sensor 120 is attached to, for example, an engine block and detects knocking by converting a force applied by vibration of the engine block resulting from knocking into an electrical signal. The knock sensor 120 includes a piezoelectric element 127 that includes a lead-free piezoelectric member 121 and electrodes 123 and 125. The piezoelectric element 127 has a configuration similar to that of the piezoelectric element 10 described above.

[0053] According to the lead-free piezoelectric composition of the present embodiment configured as described above, the lead-free piezoelectric composition has a main phase made of an alkali niobate perovskite oxide and a subphase containing a metal oxide different from the alkali niobate perovskite oxide constituting the main phase, and by setting the Young's modulus of the composition to 90 GPa or more, the rate of change in the mechanical quality factor Qm between low and high loads (low vibration stress and high vibration stress) can be suppressed. As a result, it is possible to manufacture a piezoelectric element whose piezoelectric characteristics are stable from low to high loads and which operates stably with little energy loss during operation.

[0054] Twelve types of lead-free piezoelectric compositions, samples S1 to S12, which differ in the configuration of the main phase and subphase, were prepared and evaluated for the rate of change in Qm from low load to high load.

[0055] Fig. 12 is an explanatory diagram showing the structure and evaluation results of each sample produced. Fig. 13 is an explanatory diagram showing the structure of the main phase of each sample. Fig. 13 shows the "composition of calcined powder 1" produced to form the main phase, the "additives" added to calcined powder 1, and the composition of the obtained main phase.

[0056] <Preparation of lead-free piezoelectric composition> [Sample S1] Sample S1 has a main phase shown as "main phase A1" in FIG. 13 and contains CoZnTiO ４ A lead-free piezoelectric composition was prepared having a subphase containing an oxide having a spinel structure represented by the formula (see FIG. 12). In FIG. 2, the process of mixing raw material powders of the main phase and the process of calcining the mixed raw materials are described, but when preparing the calcined powders that constitute the main phase of sample S1 and samples S2 to S12 described below, a part of the raw material powders of the main phase was mixed and then calcined to prepare calcined powder 1, and then the remaining raw material powder was mixed with calcined powder 1 and calcined to prepare calcined powder 2 as the calcined powder of the main phase. When preparing calcined powder 1, K was used as the raw material powder. ２ CO ３ Powder, Na ２ CO ３ powder, and Nb ２ O ５The powder was weighed according to the "Composition of Calcined Powder 1" shown in Figure 13. Ethanol was added to the weighed raw material powder, and wet mixing was carried out in a ball mill for 15 hours or more to obtain a slurry. The slurry was then dried, and the obtained mixed powder was calcined at 900°C for 5 hours in an air atmosphere to obtain calcined powder 1.

[0057] To the obtained calcined powder 1, an additive having a composition shown as an additive of "main phase A1" in FIG. 13 was added in the proportion shown in FIG. 13 (2.5 mol% BaCO ３ and 2.5 mol% ZrO ２ 13, the amounts of additives added for samples S1 to S12 are shown as relative amounts when the calcined powder 1 to be added is taken as 100 mol%. Ethanol was then added to the raw material powder to which the additives had been added, 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 900°C for 5 hours in an air atmosphere to obtain calcined powder 2, which was the calcined powder of the main phase.

[0058] Separately from the preparation of the calcined powder 2 of the main phase, a calcined powder of the subphase was prepared. ３ O ４ powder, ZnO powder, and TiO ２ The powder was used to obtain the subphase composition shown in FIG. ４ Ethanol was added to the weighed raw material powder, and wet mixing was carried out in a ball mill for 15 hours or more to obtain a slurry. The slurry was then dried, and the obtained mixed powder was calcined at 1200°C for 5 hours in an air atmosphere to obtain a calcined powder of the subphase (steps T130 to T140).

[0059] Then, the calcined powder 2 of the main phase and the calcined powder of the subphase were weighed, and a binder and ethanol were added thereto. The mixture was wet-mixed in a ball mill to obtain a slurry. The obtained slurry was then dried, granulated, and uniaxially pressed at a pressure of 20 MPa to form a desired shape. A cold isostatic pressing (CIP) process was then performed at a pressure of 150 MPa to obtain a compact (step T150). The obtained compact was fired at 1130°C for 5 hours in an air atmosphere (step T160) to obtain the "main phase A1" and the spinel-type oxide CoZnTiO ４ A lead-free piezoelectric composition (piezoelectric body) having a subphase constituted by the following was prepared: Sample S1. The content (volume %) of the subphase in Sample S1 and Samples S3 to S12 described below was uniformly set at 1.5 volume %.

[0060] [Sample S2] As Sample S2, a lead-free piezoelectric composition was prepared that was composed of a main phase shown as "main phase A2-1" in FIG. 13 and had no subphase. Calcined powder 1 for forming the main phase of Sample S2 was prepared in the same manner as Sample S1. Then, an additive having a composition shown as an additive for "main phase A2-1" in FIG. 13 was added to the obtained calcined powder 1 in the proportion shown in FIG. 13 (2.5 mol % BaCO ３ and 2.5 mol% ZrO ２ and 0.5 mol% MnO ２ ), and calcined powder 2 was prepared under the same conditions as sample S1.

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

[0062] [Sample S3] Sample S3 has a main phase shown as "main phase B1" in FIG. 13 and contains Ba ２ KNb ５ O １５The lead-free piezoelectric composition was prepared by adding a subphase containing an oxide having a tungsten bronze structure represented by the formula (1) (see FIG. 12). ２ CO ３ Powder, Na ２ CO ３ powder, and Nb ２ O ５ It was prepared in the same manner as the calcined powder 1 of sample S1, except that the powder mixing ratio was different from that of sample S1, as shown as "Composition of calcined powder 1" in Figure 13. In addition, the conditions for preparing calcined powder 2 by adding additives to calcined powder 1 were the same as those for sample S1.

[0063] When preparing the calcined powder of the subphase, BaCO ３ powder, K ２ CO ３ powder, and Nb ２ O ５ The powder was used to obtain the subphase composition shown in FIG. ２ KNb ５ O １５ ) were weighed out. Ethanol was added to the weighed raw material powder, and wet mixing was carried out 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 1200°C for 5 hours in an air atmosphere to obtain a calcined powder of the subphase (steps T130 to T140). A lead-free piezoelectric composition (piezoelectric body) was produced using the calcined powder 2 of the main phase and the calcined powder of the subphase in the same manner as in sample S1.

[0064] [Samples S4 to S9] For samples S4 to S9, calcined powder 2 was prepared in the same manner as sample S1, except that the types and proportions of additives added to calcined powder 1 were varied so as to provide the main phase shown in Fig. 13. Samples S4, S5, and S7 to S9 used the same subphase calcined powder as sample S3, and sample S6 used the same calcined powder as sample S1. A lead-free piezoelectric composition (piezoelectric body) was prepared using main phase calcined powder 2 and subphase calcined powder in the same manner as sample S1.

[0065] [Samples S10 to S11] Samples S10 to S11 were produced using the same main phase calcined powder 2 and subphase calcined powder as sample S7, and had the same composition, but the firing temperatures in step T160 were different. 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 for samples S10 to S11, other than the firing temperature, 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 speed at which an ultrasonic pulse propagated through the test piece. Specifically, a longitudinal wave vibrator and a shear wave vibrator were used on a mirror-polished sample to calculate the longitudinal wave velocity V from the propagation speed of the pulse. Ｉ (unit: m / s), shear wave velocity V Ｓ The elastic modulus (Young's modulus) was calculated from the measured values ​​using the following formula (7): ρ is the density of the sample (unit: kg / m ３） The density was measured using the Archimedes method. Here, density represents bulk density, which was calculated from the mass of the sample measured in air and the mass of the sample measured in liquid.

[0067]

[0068] <Evaluation Method for Lead-Free Piezoelectric Compositions> Lead-free piezoelectric compositions were evaluated based on the rate of change in mechanical quality factor Qm. The mechanical quality factor Qm at each load was measured using the electrical transient response method. The electrical transient response method is a well-known method for calculating piezoelectric properties at high vibration from the decay waveform immediately after pulse voltage application. In this example, each sample was machined into a 31-shape (rectangular, 1 mm x 3 mm x 12 mm). A burst wave of 100 V at the resonant frequency of each sample, between 100 kHz and 300 kHz, was applied to each sample using an equipment configuration consisting of a function generator (33500B), a bipolar amplifier (HAS 4052), a laser Doppler vibrometer (NLV-2500), and an oscilloscope (DLM3034). The vibration velocity and current decay waveforms were obtained immediately after the voltage application. Using the obtained measurement data, the mechanical quality factor Qm and vibration stress Tm were calculated using the following equations (8) to (10), respectively.

[0069]

[0070] where f _r is the instantaneous frequency of the vibration velocity, V is the instantaneous amplitude of the vibration velocity, β is the damping coefficient, Qm is the mechanical quality factor, s １１ Ｅ where ρ is the elastic compliance, ρ is the density of the sample, X is the length of the sample, and Tm is the equivalent amplitude (load) of the maximum stress at the center of the sample. Tm = 1 MPa is defined as a low load, and Tm = 20 MPa is defined as a high load. The rate of change in Qm was calculated using the values ​​of Qm at Tm = 1 MPa and Tm = 20 MPa. The "rate of change in Qm" was defined as the ratio (unit: %) of the "difference between the values ​​of Qm at Tm = 1 MPa and Tm = 20 MPa" to the "value of Qm at Tm = 1 MPa." In FIG. 12, a product with a rate of change in mechanical quality factor Qm of 40% or less is evaluated as a good product and indicated by "○," while a product with a rate of change in Qm of more than 40% is indicated by "×."

[0071] 12 , it was confirmed that by setting the Young's modulus of the lead-free piezoelectric composition to 90 GPa or more, the rate of change in the mechanical quality factor Qm between low and high loads (low vibration stress and high vibration stress) can be suppressed (40% or less in the examples). In this case, the Young's modulus of the lead-free piezoelectric composition may be adjusted, for example, by the composition of the main phase, subphase, etc. (see Samples S1, S3 to S9), or by the 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 set to 90 GPa or more, the rate of change in Qm can be suppressed.

[0072] The present disclosure is not limited to the above-described embodiments, and can be realized in various configurations without departing from the spirit thereof. For example, the technical features in the embodiments corresponding to the technical features in each aspect described in the Summary of the Invention section can be appropriately replaced or combined to solve some or all of the above-described problems or achieve some or all of the above-described effects. Furthermore, if a 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 comprising a main phase made of an alkali niobate perovskite oxide and a subphase containing a metal oxide different from the alkali niobate perovskite oxide constituting the main phase, wherein the lead-free piezoelectric composition has a Young's modulus of 90 GPa or more. [Application Example 2] The lead-free piezoelectric composition according to Application Example 1, wherein the Young's modulus is 100 GPa or more. [Application Example 3] The lead-free piezoelectric composition according to Application Example 1 or 2, wherein the Young's modulus is 105 GPa or more. [Application Example 4] The lead-free piezoelectric composition according to any one of Application Examples 1 to 3, wherein the metal oxide constituting the subphase includes at least one of a metal oxide having a spinel structure and a metal oxide having a tungsten bronze structure. [Application Example 5] In the lead-free piezoelectric composition according to any one of Application Examples 1 to 4, the alkali niobate perovskite oxide constituting the main phase is represented by the composition formula (A1 ａ M1 ｂ ) ｃ (Nb ｄ１ M2 ｄ２ M3 ｄ３ ) O ３＋ｅA lead-free piezoelectric composition comprising an alkali niobate perovskite oxide represented by the formula (wherein element A1 is at least one alkali metal; 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 an oxygen deficiency or excess). [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; and element M3 is Mn; and 0<a≦1. [Application Example 7] A piezoelectric element comprising: a piezoelectric body formed from the lead-free piezoelectric composition according to any one of Application Examples 1 to 6; and an electrode attached to the piezoelectric body. [Application Example 8] A device comprising the piezoelectric element according to Application Example 7. [Application Example 9] The device according to Application Example 8, wherein the device 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.

[0074] 10... Piezoelectric element 20... Piezoelectric body 31, 32... Electrode 40... Ultrasonic scalpel 41... Ultrasonic vibrator 43... Working 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... Substrate 73... Ultrasonic vibrator 75... Grinding stone 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 made of an alkali niobate perovskite oxide and a subphase containing a metal oxide different from the alkali niobate perovskite oxide constituting the main phase, the lead-free piezoelectric composition having a Young's modulus of 90 GPa or more.

2. The lead-free piezoelectric composition according to claim 1, characterized in that the Young's modulus is 100 GPa or more.

3. The lead-free piezoelectric composition according to claim 1 or 2, characterized in that the Young's modulus is 105 GPa or more.

4. A lead-free piezoelectric composition according to any one of claims 1 to 3, characterized in that the metal oxide constituting the subphase contains at least one of a metal oxide having a spinel structure and a metal oxide having a tungsten bronze structure.

5. The lead-free piezoelectric composition according to any one of claims 1 to 4, wherein the alkali niobate perovskite oxide constituting the main phase is represented by the composition formula (A1 ａ M1 ｂ ) ｃ (Nb ｄ１ M2 ｄ２ M3 ｄ３ ) O ３＋ｅ 1. A lead-free piezoelectric composition comprising an alkali niobate perovskite oxide represented by the formula (1), wherein A1 is at least one alkali metal, M1 is at least one of Ba, Ca, and Sr, M2 is at least one of Ti, Zr, Ta, Hf, Sn, Sb, and Si, and 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 an oxygen deficiency or excess.

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, and the element M3 is Mn, and 0<a≦1.

7. A piezoelectric element comprising: a piezoelectric body formed from the lead-free piezoelectric composition according to any one of claims 1 to 6; and electrodes attached to the piezoelectric body.

8. A device comprising the piezoelectric element according to claim 7.

9. The device according to claim 8, characterized in that the device 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