Lead-free piezoelectric composition, piezoelectric element, and device

Abstract

This lead-free piezoelectric composition comprises: a main phase comprising an alkali niobate-based perovskite oxide; and a sub-phase comprising a compound having a tungsten bronze structure containing Nb and at least one element selected from Ba, Ca, Sr, Na and K. The sub-phase satisfies at least one condition among the following three conditions represented by formulae (1)-(3) related to D80, D50 and D20 in a volume-based particle size distribution.　(1): 1.3 μm≤D80≤218.6 μm; (2): 0.4 μm≤D50≤68.7 μm; and (3): 0.1 μm≤D20≤22.2 μm

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)-based 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, for example, to reduce environmental impact. Alkali niobate-based perovskite oxides have been proposed as candidates for such lead-free piezoelectric compositions. However, alkali niobate-based perovskite oxides have the problem of potentially insufficient sinterability.

[0003] As a configuration for improving the sinterability of alkali niobate perovskite oxides, a configuration has been proposed in which a subphase composed of other oxides is provided in addition to a main phase composed of alkali niobate perovskite oxide in a lead-free piezoelectric composition (see, for example, Patent Documents 1 to 4). Specifically, Patent Document 1 discloses a configuration in which a subphase containing an M-Ti-O spinel compound (wherein element M is a monovalent to tetravalent element) is provided. Patent Document 2 also discloses a configuration in which a (M4,Ti)O ４ (wherein the metal element M4 is one or more of Fe, Co, and Zn) is provided as a subphase containing a spinel compound. Patent Document 3 discloses a configuration in which a subphase containing a spinel compound containing Ti is provided. Patent Document 4 discloses a configuration in which a subphase containing a spinel compound represented by composition formula A2 １－ｘ Ti １－ｘ Nb １＋ｘ O ５ (wherein element A2 is at least one alkali metal and satisfies 0≦x≦0.15), and oxides represented by the composition formula A3Ti ３ NbO ９ (wherein element A3 is at least one kind of alkali metal) is provided.

[0004] Japanese Patent No. 5715309 Japanese Patent No. 6895845 International Publication No. 2022 / 215666 International Publication No. 2023 / 026614

[0005] In such piezoelectric compositions, it is necessary to increase the mechanical quality factor Qm and reduce the dielectric loss (dielectric loss tangent) tanδ, which is the reciprocal of the mechanical quality factor Qm. The mechanical quality factor Qm is a parameter that indicates the sharpness of the resonance spectrum of a piezoelectric element, and by increasing the mechanical quality factor Qm, it is possible to effectively vibrate the piezoelectric element. However, the mechanical quality factor Qm and dielectric loss tanδ of lead-free piezoelectric compositions have not been sufficiently studied, and further improvement of the mechanical quality factor Qm and further reduction of the dielectric loss tanδ have been desired.

[0006] The present disclosure can be realized in the following aspects. [1] According to one aspect of the present disclosure, there is provided a lead-free piezoelectric composition. The lead-free piezoelectric composition includes a main phase made of an alkali niobate perovskite oxide and a subphase containing a compound having a tungsten bronze structure that includes niobium (Nb) and at least one element selected from barium (Ba), calcium (Ca), strontium (Sr), sodium (Na), and potassium (K), wherein the subphase satisfies at least one of the three conditions shown in the following formulas (1) to (3) regarding the 80% cumulative frequency particle diameter (D80), the 50% cumulative frequency particle diameter (D50), and the 20% cumulative frequency particle diameter (D20) in a volume-based particle size distribution:

[0023] According to the lead-free piezoelectric composition of this embodiment, in a lead-free piezoelectric composition having a main phase made of an alkali niobate perovskite oxide, the particle size of the subphase containing the compound having a tungsten bronze structure satisfies at least one of the three conditions shown in the above formulas (1) to (3), thereby increasing the mechanical quality factor Qm and reducing the dielectric loss tan δ of the lead-free piezoelectric composition.

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[0051] 1.3 μm≦D80≦155.2 μm ... (4) With this configuration, the mechanical quality factor Qm of the lead-free piezoelectric composition can be increased, and the effect of reducing the dielectric loss tan δ can be further enhanced. [3] In the subphase of the lead-free piezoelectric composition of the above embodiment, the particle diameter (D50) at 50% cumulative frequency in the volume-based particle size distribution satisfies the above formula (2) and may also satisfy the following formula (5): 0.4 μm≦D50≦60.7 μm ... (5) With this configuration, the mechanical quality factor Qm of the lead-free piezoelectric composition can be increased, and the effect of reducing the dielectric loss tan δ can be further enhanced.[4] In the subphase of the lead-free piezoelectric composition of the above embodiment, the particle size (D20) at 20% cumulative frequency in the volume-based particle size distribution satisfies the formula (3) above and may further satisfy the following formula (6): 0.1 μm≦D20≦6.7 μm (6) With this configuration, the lead-free piezoelectric composition can have an increased mechanical quality factor Qm and a further improved effect of reducing dielectric loss tanδ. [5] In the lead-free piezoelectric composition of the above embodiment, the alkali niobate perovskite oxide constituting the main phase may contain manganese (Mn). With this configuration, the lead-free piezoelectric composition can have an increased mechanical quality factor Qm and a further improved effect of reducing dielectric loss tanδ. [6] In the lead-free piezoelectric composition of the above embodiment, the alkali niobate perovskite oxide constituting the main phase may contain manganese (Mn). With this configuration, the lead-free piezoelectric composition can have an increased mechanical quality factor Qm and a further improved effect of reducing dielectric loss tanδ. ａ M1 ｂ ) ｃ (Nb ｄ１ , Mn ｄ２ , M2 ｄ３ ) O ３＋ｅand b / (d2+d3)>1.0. (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 and Zr; 0<a<1, 0<b<1, a+b=1; c satisfies 0.80<c<1.10; 0<d1<1, 0<d2<1, 0<d3<1, d1+d2+d3=1; and e is a value indicating oxygen deficiency or excess), and b / (d2+d3)>1.0 may be satisfied. With this configuration, the mechanical quality factor Qm of the lead-free piezoelectric composition can be increased, and the effect of reducing dielectric loss tanδ can be further enhanced. [7] According to another aspect of the present disclosure, there is provided a piezoelectric element comprising: a piezoelectric body formed from the lead-free piezoelectric composition according to any one of [1] to [6]; and electrodes attached to the piezoelectric body. According to this aspect of the piezoelectric element, the piezoelectric element includes a piezoelectric body formed from a lead-free piezoelectric composition having an increased mechanical quality factor Qm and a reduced dielectric loss tan δ, thereby improving piezoelectric performance. [8] According to yet another aspect of the present disclosure, there is provided a device including the piezoelectric element described in [7]. According to this aspect of the device, the device includes a piezoelectric element including a lead-free piezoelectric composition having an increased mechanical quality factor Qm and a reduced dielectric loss tan δ, thereby improving the performance of the entire device. The present disclosure can be realized in various forms, for example, in the form of a lead-free piezoelectric composition, a piezoelectric element using the same, various devices including a piezoelectric element (e.g., a knock sensor, an ultrasonic vibrator, a cutting tool, an ultrasonic sensor, an actuator), and a method for manufacturing a lead-free piezoelectric composition.

[0007] 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 of a knock sensor as an example of an apparatus; 12 is an explanatory diagram showing the configuration and evaluation results of each sample; 13 is an explanatory diagram showing the configuration and evaluation results of each sample; 14 is an explanatory diagram showing the configuration of the main phase of each sample; 15 is an explanatory diagram related to subphase calcined powder for forming the subphase of each sample.

[0008] 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 compound having a tungsten bronze structure containing niobium (Nb) and at least one element selected from barium (Ba), calcium (Ca), strontium (Sr), sodium (Na), and potassium (K). The subphase satisfies at least one of the three conditions shown in the following formulas (1) to (3) regarding the 80% cumulative frequency particle diameter (D80), the 50% cumulative frequency particle diameter (D50), and the 20% cumulative frequency particle diameter (D20) in a volume-based particle size distribution:

[0009] 1.3μm≦D80≦218.6μm… (1) 0.4μm≦D50≦68.7μm… (2) 0.1μm≦D20≦22.2μm… (3)

[0010] (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.

[0011] The alkali niobate perovskite oxide constituting the main phase may contain manganese (Mn), which is thought to improve the mechanical quality factor Qm by dissolving as an acceptor in the niobium site (B site of the perovskite crystal structure).

[0012] The alkali niobate perovskite oxide constituting the main phase is preferably an alkali niobate perovskite oxide that satisfies the following composition formula (7):

[0013] (A1 ａ M1 ｂ ) ｃ (Nb ｄ１ , Mn ｄ２ , M2 ｄ３ ) O ３＋ｅ … (7)

[0014] 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 and Zr, 0<a<1, 0<b<1, a+b=1, c satisfies 0.80<c<1.10, 0<d1<1, 0<d2<1, 0<d3<1, d1+d2+d3=1, e is a value indicating oxygen deficiency or excess, and b / (d2+d3)>1.0 is satisfied.

[0015] In the composition formula (7), the elements A1 and M1 are located at the A site of the perovskite structure, and Nb (niobium), Mn (manganese), and M2 are located at the B site. The values ​​of the coefficients a to e in the composition formula (7) 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 (7), the following are excluded: a = 0 (a composition that does not contain an alkali metal), b = 0 (a composition that does not contain any of Ca, Sr, and Ba), d1 = 0 (a composition that does not contain Nb), d2 = 0 (a composition that does not contain Mn), and d3 = 0 (a composition that does not contain either Ti or Zr).

[0016] 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 such that 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.

[0017] In the composition formula (7), the coefficients b, d2, and d3 satisfy the aforementioned relationship "b / (d2 + d3) > 1.0," thereby enhancing the mechanical quality factor Qm of the lead-free piezoelectric composition. The reason for this is presumed to be as follows. It is believed that the mechanical quality factor Qm is improved by Mn dissolving in the Nb site as an acceptor. However, Mn is difficult to dissolve in alkali niobate perovskite oxides and is prone to segregation as a heterophase in the lead-free piezoelectric composition. The ease of dissolution is believed to depend on the ionic radius and valence of the dissolved metal atom. It is believed that trivalent Mn is difficult to dissolve in the B site, where pentavalent Nb is primarily located. On the other hand, divalent elements Ba, Ca, and Sr are easily dissolved in the A site, where monovalent alkali metals are located. It is also presumed that the presence of appropriate amounts of Ba, Ca, and Sr, which have valences similar to that of Mn, in the A site helps Mn to dissolve in the B site. By adjusting the composition ratio of Mn to Ba, Ca, and Sr so that "b / (d2+d3)>1.0", an appropriate amount of Mn is dissolved in the B site, improving the mechanical quality factor Qm. There are no particular restrictions on the upper limit of "b / (d2+d3)", but it is preferable that "b / (d2+d3)≦2.0".

[0018] (A-2) Regarding the Subphase: As described above, the subphase of the lead-free piezoelectric composition of the present embodiment includes a compound having a tungsten bronze structure that includes niobium (Nb) and at least one element selected from barium (Ba), calcium (Ca), strontium (Sr), sodium (Na), and potassium (K). Here, the compound having a tungsten bronze structure is a compound represented by the following formula (8):

[0019] A ｋ B ｌ O １５＋δ … (8)

[0020] In the formula, A contains two or more monovalent or divalent elements, and B contains one or more divalent to pentavalent elements. Furthermore, while the standard values ​​of k, l, and δ are k=3, l=5, and δ=0, respectively, they may deviate from the standard values ​​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, and the compound may also contain impurity elements. Specific examples of the compound represented by the formula (8) include Ba, ３ Nb ５ O １５ , Ba ２ KNb ５ O １５ , Ba ２ NaNb ５ O １５ Furthermore, the subphase may contain other types of compounds, such as spinel compounds, as long as the degree to which the properties of the subphase are changed by the inclusion of a compound having a tungsten bronze crystal structure is within an acceptable range.

[0021] Although the compound having a tungsten bronze structure that constitutes the subphase does not have piezoelectric properties, its presence in the main phase composed of an alkali niobate perovskite oxide improves the sinterability of the piezoelectric composition, improving its structural stability and piezoelectric properties. From the viewpoint of ensuring 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. Furthermore, from the viewpoint of ensuring 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. Whether or not a compound that constitutes the subphase has a tungsten bronze structure can be determined by Rietveld analysis using the diffraction results of powder X-ray diffraction (XRD).

[0022] As described above, the subphase of the lead-free piezoelectric composition of the present embodiment satisfies at least one of the three conditions shown in the following formulas (1) to (3) regarding the 80% cumulative frequency particle diameter (D80), the 50% cumulative frequency particle diameter (D50), and the 20% cumulative frequency particle diameter (D20) in the volume-based particle size distribution.

[0023] 1.3μm≦D80≦218.6μm… (1) 0.4μm≦D50≦68.7μm… (2) 0.1μm≦D20≦22.2μm… (3)

[0024] To determine the D80, D50, and D20 values, a sintered body, which is the target lead-free piezoelectric composition, is mirror-polished and subjected to a conductive treatment, and then a backscattered electron image is taken at 500 to 3000 magnifications using an electron probe microanalyzer (EPMA). The backscattered electron image is then binarized using image analysis software to classify the main phase and subphase. The particle diameter equivalent to a circle is then calculated from the area of ​​each particle in the obtained subphase, and the D80, D50, and D20 values ​​can be determined.

[0025] In the subphase of the lead-free piezoelectric composition of this embodiment, the particle diameter (D80) at 80% cumulative frequency in the volume-based particle size distribution satisfies the above-described formula (1) and preferably also the following formula (4), which allows the lead-free piezoelectric composition to achieve a higher mechanical quality factor Qm and a lower dielectric loss tanδ.

[0026] 1.3μm≦D80≦155.2μm… (4)

[0027] Furthermore, in the subphase of the lead-free piezoelectric composition of this embodiment, it is desirable that the particle diameter at 50% cumulative frequency (D50) in the volume-based particle size distribution satisfies the above-described formula (2) and further satisfies the following formula (5), which allows the lead-free piezoelectric composition to achieve a higher mechanical quality factor Qm and a lower dielectric loss tanδ.

[0028] 0.4μm≦D50≦60.7μm… (5)

[0029] Furthermore, in the subphase of the lead-free piezoelectric composition of this embodiment, the particle diameter (D20) at 20% cumulative frequency in the volume-based particle size distribution satisfies the above-described formula (3) and preferably also the following formula (6), which allows the lead-free piezoelectric composition to achieve a higher mechanical quality factor Qm and a lower dielectric loss tanδ.

[0030] 0.1μm≦D20≦6.7μm… (6)

[0031] 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.

[0032] (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 ３ Powder, 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).

[0033] In the above description, the calcined powder is produced by mixing raw materials in step T110 and calcining 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. In this manner, calcined powder of the main phase may be produced.

[0034] 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 desired composition. The raw material powders can be oxides, carbonates, or hydroxides of the elements contained in the compound having a tungsten bronze structure that constitutes the subphase. Specifically, BaCO ３ powder, CaCO ３ Powder, SrCO ３ Powder, Na ２ CO ３ powder, K ２ CO ３ powder, Nb ２ O ５ Powders, etc. are selected as needed and weighed. Ethanol is then added to these raw material powders, and the mixture is wet-mixed in a ball mill to obtain a slurry. Wet mixing using a ball mill is preferably performed for 15 hours or more. The slurry is then dried to obtain a mixed powder, and the resulting 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 subphase (step T140). By changing the calcination temperature in step T140, the particle size and particle size distribution of the calcined powder of the subphase can be adjusted, and as a result, the particle size and particle size distribution (D80, D50, D20, etc.) of the subphase in the lead-free piezoelectric composition can be adjusted.

[0035] 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 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. 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 (step T160). The particle size and particle size distribution of the subphase in the lead-free piezoelectric composition can be adjusted by changing the sintering temperature in step T160, along with the particle size and particle size distribution of the calcined powder of the subphase, as described above.

[0036] 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. To stabilize the characteristics of the piezoelectric body obtained in this way, an annealing treatment is performed in air at 100°C for 2 hours (step T170). After that, 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.

[0037] 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 strictly controlled, which makes it possible to increase the yield of the lead-free piezoelectric composition.

[0038] 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.

[0039] (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.

[0040] (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.

[0041] (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.

[0042] (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.

[0043] 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.

[0044] (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.

[0045] (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.

[0046] (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.

[0047] (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.

[0048] (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.

[0049] According to the lead-free piezoelectric composition of the present embodiment configured as described above, in the lead-free piezoelectric composition having a main phase made of an alkali niobate perovskite oxide, the sinterability is improved by providing a subphase containing a compound having the above-mentioned tungsten bronze structure. Furthermore, by satisfying at least one of the three conditions shown in the above-mentioned formulas (1) to (3) regarding the particle diameters D80, D50, and D20 of the subphase, the mechanical quality factor Qm of the lead-free piezoelectric composition can be increased and the dielectric loss tanδ can be reduced.

[0050] Twenty-seven types of lead-free piezoelectric compositions, samples S1 to S27, which differ in the structure of the main phase and subphase, were prepared and evaluated for mechanical quality factor Qm and dielectric loss tan δ.

[0051] 12 to 14 are explanatory diagrams showing the structure and evaluation results of each sample. Fig. 15 is an explanatory diagram showing the structure of the main phase of each sample. Fig. 16 is an explanatory diagram showing the subphase calcined powder for forming the subphase of each sample.

[0052] <Preparation of lead-free piezoelectric composition> [Sample S1] As sample S1, a lead-free piezoelectric composition composed of a main phase and no subphase was prepared. In FIG. 2, the process of mixing the raw material powders of the main phase and the process of calcining the mixed raw materials are described. However, in this example, a part of the raw material powders of the main phase was mixed and 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 ５ The powder was used and weighed out according to the "Composition of Calcined Powder 1" shown in Figure 15. Ethanol was added to the weighed raw material powder, and wet mixing was carried out in a ball mill for 15 hours to obtain a slurry. The slurry was then dried, and the obtained mixed powder was calcined in an air atmosphere at 600 to 1100°C for 1 to 10 hours to obtain calcined powder 1.

[0053] To the obtained calcined powder 1, additives having the composition shown as the additives for sample S1 in FIG. 15 were added in the proportions shown in FIG. 15. Here, the amounts of additives added shown in FIG. 15 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 to obtain a slurry. The slurry was then dried, and the resulting mixed powder was calcined in an air atmosphere at 600 to 1100°C for 1 to 10 hours to obtain calcined powder 2, which is the calcined powder of the main phase.

[0054] Ethanol and a binder were added to the calcined powder 2 and 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 the 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 in an air atmosphere at 900°C to 1300°C for 1 to 10 hours (corresponding to step T160) to produce a lead-free piezoelectric composition (piezoelectric body) of sample S1. The composition of the main phase of sample S1 obtained in this manner is shown in Figure 15. The main phase constituting sample S1 and samples S2 to S24, described below, is also referred to as "main phase A" (see Figures 12 to 15).

[0055] [Samples S2 to S7] Samples S2 to S7 have the same main phase (main phase A) as sample S1, and Ba ２ KNb ５ O １５ A lead-free piezoelectric composition was prepared having a subphase containing a compound having a tungsten bronze structure represented by the formula (1) (see FIG. 12). The calcined powder for forming the main phase was prepared in the same manner as the calcined powder 2 described for sample S1.

[0056] To prepare samples S2 to S7, BaCO ３ powder, K ２ CO ３ powder, and Nb ２ O ５The powders were weighed according to the composition of the subphase. Ethanol was then added to these raw material powders and wet-mixed in a ball mill for 15 hours to obtain a slurry. The slurry was then dried to obtain a mixed powder, and the resulting mixed powder was calcined in an air atmosphere at 600 to 1300°C for 1 to 10 hours to produce a calcined powder of the subphase (step T140). The calcined powder 2 of the main phase and the calcined powder of the subphase were then weighed, and a binder and ethanol were added. The resulting slurry was then dried, granulated, and uniaxially pressed at a pressure of 20 MPa to form the desired shape. A CIP process was then performed at a pressure of 150 MPa to obtain a compact (step T150). The resulting compact was fired in an air atmosphere at 900 to 1300°C for 1 to 10 hours (step T160) to produce piezoelectric bodies as lead-free piezoelectric compositions of samples S2 to S7. The subphase content (vol %) in samples S2 to S7 was uniformly set to 1.5 vol %.

[0057] Here, for samples S2 to S7, the particle size distribution of the calcined powder of the subphase was changed by changing the calcination temperature in step T140, and further, the particle size distribution of the subphase in the lead-free piezoelectric composition was changed by changing the firing temperature in step T160. Specifically, samples S2 to S5 were produced using calcined powders calcined at the same calcination temperature (D20 = 0.05 μm, D50 = 0.2 μm, D80 = 0.5 μm), while samples S6 and S7 were produced using calcined powders calcined at a different calcination temperature from samples S2 to S5 (D20 = 15 μm, D50 = 30 μm, D80 = 80 μm) (see FIG. 16 ). The calcined powder of the subphase used in samples S2 to S5 is also referred to as “calcined powder α,” and the calcined powder of the subphase used in samples S6 and S7 is also referred to as “calcined powder β.” The particle size of the calcined powder of the subphase used in each sample shown in Fig. 16 was measured using a laser diffraction / scattering particle size distribution analyzer (LA-750, manufactured by Horiba, Ltd.) In addition, in step T160, the firing temperatures shown in Fig. 16 were adopted for each of samples S2 to S7.

[0058] [Samples S8 to S12] Samples S8 to S12 were prepared as lead-free piezoelectric compositions (piezoelectric bodies) having the same main phase (main phase A) as sample S2, but differing from sample S2 in the composition of the compound having a tungsten bronze structure that constitutes the subphase (see FIG. 12). ３ Powder, SrCO ３ powder, K ２ CO ３ powder, and Nb ２ O ５ The powder was used as the raw material powder for the subphase. ３ powder, CaCO ３ powder, K ２ CO ３ powder, and Nb ２ O ５ The powder was used as the raw material powder for the subphase. ３ Powder, Na ２ CO ３ powder, and Nb ２ O ５ The powder was used as the raw material powder for the subphase. ３ Powder, Na ２ CO ３ powder, and Nb ２ O ５ The powder was used as the raw material powder for the subphase. ３ Powder, Na ２ CO ３ powder, K ２ CO ３ powder, and Nb ２ O ５ The powder was used as the raw material powder for the subphase. Then, for each of samples S8 to S12, subphase calcined powders were produced with the composition and particle size shown in Figure 16. Samples S8 to S12 were produced under the same conditions as sample S2, except that the composition of the subphase calcined powder was different. In samples S8 to S12, the subphase content (volume %) was also uniform at 1.5 volume %.

[0059] [Samples S13 to S19] Samples S13 to S19 were prepared as lead-free piezoelectric compositions (piezoelectric bodies) having the same main phase (main phase A) as sample S2, the same composition of the compound having a tungsten bronze structure constituting the subphase as sample S2, but the particle size of the calcined powder of the subphase was different from that of sample S2 (see FIGS. 12 and 16 ). For samples S13 to S19, the particle size distribution of the calcined powder used to form the subphase was adjusted by classifying the calcined powder β used in samples S6 and S7. Samples S13 to S19 were prepared under the same conditions as sample S2, except for the different particle size distributions of the subphase calcined powder and the firing temperature in step T160 being 1150°C. The subphase content (volume %) of samples S13 to S19 was also uniform at 1.5% by volume.

[0060] [Samples S20 to S24] Samples S20 to S24 were prepared as lead-free piezoelectric compositions (piezoelectric bodies) having the same main phase (main phase A) as sample S2 and the same subphase composition as sample S2 formed using calcined powder α, but with different subphase content ratios (see FIGS. 13 and 16). The subphase content ratios (volume %) in samples S20 to S24 are shown as "subphase amount" in FIG. 13. Samples S20 to S24 were prepared under the same conditions as sample S2.

[0061] [Samples S25-S27] Samples S25-S27 were prepared as lead-free piezoelectric compositions (piezoelectric bodies) having the same subphase as Sample S2 but different main phase compositions (see FIGS. 15 and 16). As shown in FIG. 15, Samples S25-S27 used the same calcined powder 1 as Sample S2 to prepare the calcined powder of the main phase. However, the types and proportions of additives added to Calcined Powder 1 to prepare Calcined Powder 2 were different, resulting in different main phase compositions. Samples S25-S27 were prepared under the same conditions as Sample S2, except for the types and proportions of additives added to Calcined Powder 1. The subphase content (volume %) of Samples S25-S27 was also uniform at 1.5 volume %.

[0062] <Method for Evaluating Mechanical Quality Factor Qm and Dielectric Loss Tangent δ> Measurements were performed on each sample using an impedance analyzer (Keysight Technologies, E4990A), and tangent δ at room temperature and 1 kHz was calculated. The mechanical quality factor Qm was also determined using the resonance-antiresonance method. The mechanical quality factor Qm was evaluated as "Good" if the value was 500 or greater, "Fair" if the value was 200 or greater but less than 500, and "Poor" if the value was less than 200 (see Figures 12 to 14). The dielectric loss tangent δ was evaluated as "Good" if the value was 1.0% or less, "Fair" if the value was greater than 1.0% but less than 2.5%, and "Poor" if the value was greater than 2.5% (see Figures 12 to 14).

[0063] <Method for calculating subphase particle size and subphase amount (volume %)> The sintered body of each sample was mirror-polished and subjected to a conductive treatment, and then a backscattered electron image was taken at 500 to 3000 magnifications using an electron probe microanalyzer (EPMA). The obtained backscattered electron images were then binarized using image analysis software to classify the subphase into a main phase and a subphase. The circle-equivalent particle size was then calculated from the area of ​​each particle of the obtained subphase, and D80, D50, and D20 were determined (see Figures 12 to 14). Furthermore, after classifying the subphase into a main phase and a subphase by binarizing the backscattered electron images using image analysis software as described above, the subphase amount (volume %) was calculated from the area ratio of the obtained main phase to the subphase.

[0064] <Method of Analyzing Each Phase> The element ratios of the main phase and subphase in each sample were measured using an EPMA-WDS (wavelength dispersive X-ray spectrometer) and an EPMA-EDS (energy dispersive X-ray spectrometer). Whether the subphase in each sample was a tungsten bronze-type compound was determined by Rietveld analysis using the diffraction results of powder X-ray diffraction (XRD).

[0065] <Evaluation Results> In Figures 12 to 14, the overall evaluation results for each sample are shown in the "Judgment" column. If at least one of the evaluation results for the mechanical quality factor Qm and the dielectric loss tan δ of each sample was "X", the overall evaluation was rated as "X". Of the remaining samples that did not receive an overall evaluation of "X", if at least one of the evaluation results for the mechanical quality factor Qm and the dielectric loss tan δ was "△", the overall evaluation was rated as "△". Furthermore, the overall evaluation of the remaining samples, i.e., samples for which both the evaluation results for the mechanical quality factor Qm and the dielectric loss tan δ were "○", was rated as "○".

[0066] As shown in FIGS. 12 to 14 , the lead-free piezoelectric composition comprises a main phase made of an alkali niobate perovskite oxide and a subphase containing a compound having a tungsten bronze structure containing Nb and at least one selected from Ba, Ca, Sr, Na, and K. It has been confirmed that by satisfying at least one of the three conditions shown in the above-described formulas (1) to (3) regarding D80, D50, and D20 related to the particle size distribution of the subphase, it is possible to obtain the effects of increasing the mechanical quality factor Qm and reducing the dielectric loss tanδ (comparison of samples S2 to S6 and S8 to S27 with samples S1 and S7). The evaluation result of the dielectric loss tan δ for both sample S1 having no subphase and sample S7 which does not satisfy all three conditions shown in the above-mentioned formulas (1) to (3) was "X". However, it is considered that the value of the dielectric loss tan δ of sample S1 having no subphase is larger than that of sample S7 having a subphase because sample S1 has a less dense (sinterable) structure and therefore has a more unstable structure.

[0067] Specifically, it was confirmed that not only samples S2-S6, in which all of D80, D50, and D20 related to the particle size distribution of the subphase satisfy the formulas (1)-(3), but also samples S13-S19, in which at least one of D80, D50, and D20 satisfies the formulas (1)-(3), exhibit the effect of increasing the mechanical quality factor Qm and reducing the dielectric loss tanδ compared to sample S7, in which none of D80, D50, and D20 satisfies the formulas (1)-(3). In Figures 12-14, cases in which D80, D50, and D20 do not satisfy the formulas (1)-(3) are indicated by hatching.

[0068] Furthermore, as shown in samples S8-S12, it was confirmed that similar effects of increasing the mechanical quality factor Qm and reducing the dielectric loss tan δ could be achieved even if the composition of the subphase was varied, as long as the conditions for the subphases expressed by the above-mentioned formulas (1)-(3) were satisfied. Furthermore, as shown in samples S20-S24, it was confirmed that similar effects of increasing the mechanical quality factor Qm and reducing the dielectric loss tan δ could be achieved even if the subphase content was varied, for example, within the range of 0.5-10.0 vol% (see FIG. 13). It was confirmed that the effect of increasing the mechanical quality factor Qm and reducing the dielectric loss tan δ was particularly enhanced by setting the subphase content to 0.5-7.0 vol%. Furthermore, as shown in samples S2 and S25-S27, it was confirmed that similar effects of increasing the mechanical quality factor Qm and reducing the dielectric loss tan δ could be achieved even if the composition of the alkali niobate perovskite oxide constituting the main phase and exhibiting piezoelectricity was varied (see FIG. 14).

[0069] 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.

[0070] 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 compound having a tungsten bronze structure containing niobium (Nb) and at least one element selected from barium (Ba), calcium (Ca), strontium (Sr), sodium (Na), and potassium (K), wherein the subphase satisfies at least one of the three conditions shown in the following formulas (1) to (3) regarding a cumulative frequency 80% particle diameter (D80), a cumulative frequency 50% particle diameter (D50), and a cumulative frequency 20% particle diameter (D20) in a volume-based particle size distribution: 1.3 μm≦D80≦218.6 μm (1) 0.4 μm≦D50≦68.7 μm (2) 0.1 μm≦D20≦22.2 μm (3) [Application Example 2] The lead-free piezoelectric composition according to Application Example 1, wherein the subphase has a cumulative 80% particle size (D80) in a volume-based particle size distribution that satisfies the formula (1) and further satisfies the following formula (4): 1.3 μm≦D80≦155.2 μm (4) [Application Example 3] The lead-free piezoelectric composition according to Application Example 1 or 2, wherein the subphase has a cumulative 50% particle size (D50) in a volume-based particle size distribution that satisfies the formula (2) and further satisfies the following formula (5): 0.4 μm≦D50≦60.7 μm ... (5) [Application Example 4] The lead-free piezoelectric composition according to any one of Application Examples 1 to 3, wherein the subphase has a particle size (D20) at 20% cumulative frequency in a volume-based particle size distribution that satisfies the formula (3) and further satisfies the following formula (6): 0.1 μm≦D20≦6.7 μm ... (6) [Application Example 5] The lead-free piezoelectric composition according to any one of Application Examples 1 to 4, wherein the alkali niobate perovskite oxide constituting the main phase contains manganese (Mn).Application Example 6 In the lead-free piezoelectric composition according to any one of Application Examples 1 to 5, the alkali niobate perovskite oxide constituting the main phase is represented by the composition formula (A1. ａ M1 ｂ ) ｃ (Nb ｄ１ , Mn ｄ２ , M2 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 and Zr; 0<a<1, 0<b<1, a+b=1; c satisfies 0.80<c<1.10; 0<d1<1, 0<d2<1, 0<d3<1, d1+d2+d3=1; and e is a value indicating an oxygen deficiency or excess), and wherein b / (d2+d3)>1.0 is satisfied. [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 electrodes 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, 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.

[0071] 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 compound having a tungsten bronze structure containing niobium (Nb) and at least one selected from barium (Ba), calcium (Ca), strontium (Sr), sodium (Na) and potassium (K), wherein the subphase satisfies at least one of the three conditions shown in the following formulas (1) to (3) regarding the 80% cumulative frequency particle diameter (D80), the 50% cumulative frequency particle diameter (D50), and the 20% cumulative frequency particle diameter (D20) in a volume-based particle size distribution: 1.3 μm≦D80≦218.6 μm ... (1) 0.4 μm≦D50≦68.7 μm ... (2) 0.1 μm≦D20≦22.2 μm ... (3) 2. The lead-free piezoelectric composition according to claim 1, wherein the subphase has a cumulative frequency 80% particle size (D80) in a volume-based particle size distribution that satisfies the formula (1) and further satisfies the following formula (4): 1.3 μm≦D80≦155.2 μm ... (4) 3. The lead-free piezoelectric composition according to claim 1 or 2, wherein the subphase has a cumulative frequency 50% particle size (D50) in a volume-based particle size distribution that satisfies the formula (2) and further satisfies the following formula (5): 0.4 μm≦D50≦60.7 μm ... (5) 4. The lead-free piezoelectric composition according to any one of claims 1 to 3, wherein the particle size (D20) at 20% cumulative frequency in the volume-based particle size distribution of the subphase satisfies the formula (3) and further satisfies the following formula (6): 0.1 μm≦D20≦6.7 μm ... (6) 5. A lead-free piezoelectric composition according to any one of claims 1 to 4, characterized in that the alkali niobate perovskite oxide constituting the main phase contains manganese (Mn).

6. The lead-free piezoelectric composition according to any one of claims 1 to 5, wherein the alkali niobate perovskite oxide constituting the main phase is represented by the composition formula (A1 ａ M1 ｂ ) ｃ (Nb ｄ１ , Mn ｄ２ , M2 ｄ３ ) O ３＋ｅ 1. A lead-free piezoelectric composition comprising a main phase made of an alkali niobate perovskite-type oxide represented by the formula (1), (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 and Zr, 0<a<1, 0<b<1, a+b=1, c satisfies 0.80<c<1.10, 0<d1<1, 0<d2<1, 0<d3<1, d1+d2+d3=1, and e is a value indicating an oxygen deficiency or excess), and wherein b / (d2+d3)>1.0 is satisfied.

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.

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