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

Abstract

To achieve a long life by increasing a limit vibration speed Vmax in a piezoelectric element containing a lead-free piezoelectric ceramic composition as a main component.SOLUTION: The lead-free piezoelectric ceramic composition contains an alkali niobate-based perovskite oxide, and has a limit vibration speed (Vmax) of 0.8m / s or more when the limit vibration speed (Vmax) is defined as a vibration speed at which a temperature rise at a vibration node of a vibrator reaches 20°C in a state where the piezoelectric vibrator is resonantly driven at room temperature. The piezoelectric element 200 has a piezoelectric layer 100 containing such a lead-free piezoelectric ceramic composition and an electrode 301,302 in contact with the piezoelectric layer 100.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a lead-free piezoelectric ceramic composition, a piezoelectric element, and a device including the piezoelectric element. [Background technology]

[0002] Japanese Patent Laid-Open Publication No. 2006-199524 (Patent Document 1 below) discloses a piezoelectric ceramic composition whose main component is multi-component lead zirconate titanate. In a PZT-based piezoelectric material, a high piezoelectric constant can be expected by substituting a portion of Pb with Sr, which has low electronegativity.

[0003] Furthermore, paragraph 0031 of Patent Document 1 states that "the improvement in Kr characteristics is believed to be due to the effect of ceramic crystal grain growth," and it is presumed that the piezoelectric ceramic composition obtained in Patent Document 1 has high crystallinity. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-199524 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the above-mentioned piezoelectric ceramic compositions are composed of PZT-based materials, and the lead component contained in PZT is a cause of environmental load and is therefore viewed as problematic. In recent years, progress has been made in the development of piezoelectric elements whose main component is lead-free piezoelectric ceramic compositions that do not contain lead.

[0006] The present disclosure has been made in view of the above circumstances, and aims to realize a longer life by increasing the critical vibration velocity Vmax in a piezoelectric element containing a lead-free piezoelectric ceramic composition as a main component. [Means for solving the problem]

[0007] The lead-free piezoelectric ceramic composition of the present disclosure is a lead-free piezoelectric ceramic composition containing an alkali niobate perovskite oxide, and is characterized in that, when the critical vibration velocity (Vmax) is defined as the vibration velocity at which the temperature rise at the vibration node of a vibrator reaches 20°C while the vibrator is resonantly driven at room temperature, the critical vibration velocity (Vmax) is 0.8 m / s or more. [Effects of the Invention]

[0008] According to the present disclosure, a longer life can be achieved by increasing the critical vibration velocity Vmax in a piezoelectric element containing a lead-free piezoelectric ceramic composition as a main component. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a perspective view of a piezoelectric element according to a first embodiment. [Figure 2] FIG. 2 is a cross-sectional view of a piezoelectric element according to the second embodiment. [Figure 3] FIG. 3 is a schematic diagram showing an ultrasonic scalpel. [Figure 4] FIG. 4 is a schematic diagram showing an ultrasonic scaler. [Figure 5] FIG. 5 is a schematic diagram showing an ultrasonic cleaner. [Figure 6] FIG. 6 is a schematic diagram showing an ultrasonic processing machine. [Figure 7] FIG. 7 is a schematic diagram showing a piezoelectric transducer. [Figure 8] FIG. 8 is a schematic diagram showing an ultrasonic motor. [Figure 9] FIG. 9 is a schematic diagram showing a piezoelectric gyro sensor. [Figure 10] FIG. 10 is a schematic diagram showing a piezoelectric filter. [Figure 11] FIG. 11 is a schematic diagram showing a knock sensor. [Figure 12] FIG. 12 is a diagram showing the correlation between the composition of the main phase of the lead-free piezoelectric ceramic compositions according to Examples 1 to 4 and the firing conditions in the firing step. [Figure 13]FIG. 13 is a diagram showing the correlation between the composition of the lead-containing piezoelectric ceramic composition according to Comparative Example 1 and the firing conditions in the firing step. [Figure 14] FIG. 14 is a graph showing the correlation between the vibration velocity and the temperature rise during resonant driving of each sample according to Examples 1 to 4 and Comparative Example 1. [Figure 15] FIG. 15 is a diagram showing the correlation between Vmax and Δ(d31×Qm) for each sample according to Examples 1 to 4 and Comparative Example 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] First, embodiments of the present disclosure will be listed and described. <1> The lead-free piezoelectric ceramic composition of the present disclosure is a lead-free piezoelectric ceramic composition containing an alkali niobate perovskite oxide, and is characterized in that, when the critical vibration velocity (Vmax) is defined as the vibration velocity at which the temperature rise at the vibration node of a vibrator reaches 20°C while the vibrator is resonantly driven at room temperature, the critical vibration velocity (Vmax) is 0.8 m / s or more.

[0011] According to the present disclosure, self-heating due to resonant driving of a piezoelectric vibrator is suppressed, thereby making it possible to realize a longer life for a piezoelectric device that uses a lead-free piezoelectric ceramic composition.

[0012] <2> <1> In the lead-free piezoelectric ceramic composition described in the above, the vibration stress is d 31 × d when vibration stress is high (Tm = 20 MPa) for the value of Qm 31 ×Qm value change rate Δ(d 31 × Qm) (%) is preferably 70 or less.

[0013] Generally, the piezoelectric constant d of a piezoelectric vibrator formed from a lead-free piezoelectric ceramic composition is 31 is the piezoelectric constant d of the piezoelectric vibrator formed by the leaded piezoelectric ceramic composition 31Therefore, in order to ensure that a piezoelectric vibrator made of a lead-free piezoelectric ceramic composition has the same vibration speed as a piezoelectric vibrator made of a lead-containing piezoelectric ceramic composition, a relatively high voltage is often required. In order to resonantly drive a piezoelectric vibrator made of a lead-free piezoelectric ceramic composition at a lower voltage, it is necessary to consider not only the mechanical quality factor Qm but also the piezoelectric constant d 31 It is also preferable to consider the vibration stress d 31 × The value of Qm when the vibration stress is high (Tm = 20 MPa) 31 ×Qm value change rate Δ(d 31 ×Qm), the smaller the resonant drive of the piezoelectric vibrator becomes. 31 When the value of (Qm) is within the above range, the self-heating of the piezoelectric vibrator is reduced, and the piezoelectric vibrator is allowed to perform stable resonant driving.

[0014] <3> <1> or <2> The lead-free piezoelectric ceramic composition described in 1 above preferably comprises a main phase containing the alkali niobate-based perovskite oxide and a subphase containing an M-Ti-O-based spinel compound.

[0015] In this case, the vacancies formed in the main phase are filled with the subphase containing the M-Ti-O based spinel compound, thereby stabilizing the structure of the main phase.

[0016] <4> The piezoelectric element of the present disclosure comprises: <1> from <3> and an electrode in contact with the piezoelectric layer.

[0017] According to the present disclosure, it is possible to provide a piezoelectric element that suppresses self-heating and has a longer lifespan.

[0018] <5> The device of the present disclosure comprises: <4> The piezoelectric element is provided as described above.

[0019] <6> <5> The device described in may be selected from the group consisting 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.

[0020] According to the present disclosure, various devices having heat durability are provided.

[0021] <Details of the embodiment> The lead-free piezoelectric ceramic composition and piezoelectric element according to the present embodiment will be described below with reference to the drawings.

[0022] <Configuration of lead-free piezoelectric ceramic composition> The lead-free piezoelectric ceramic composition is mainly composed of an alkali niobate perovskite oxide, that is, the lead-free piezoelectric ceramic composition contains an alkali niobate perovskite oxide as a main phase.

[0023] The alkali niobate perovskite oxide contained in the main phase is represented by the following composition formula (1).

[0024] (K a Na b Li c A d ) e (B f C g )O h ...Composition formula (1)

[0025] Element A is at least one of Ca (calcium), Sr (strontium), and Ba (barium). Element B is at least one of Nb (niobium), Ta (tantalum), Ti (titanium), Zr (zirconium), Hf (hafnium), Sn (tin), Sb (antimony), and Si (silicon), including at least Nb. Element C is at least one of Mg (magnesium), Al (aluminum), Sc (scandium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Zn (zinc), Ga (gallium), and Y (yttrium). a+b+c+d=1, a+b+c is not zero, e is arbitrary, f+g=1, and h is an arbitrary value that constitutes a perovskite.

[0026] The above composition formula (1) can be rewritten as the following composition formula (1A).

[0027] (K a Na b Li c A1 d1 A2 d2 ) e (B1 f1 B2 f2 B3 f3 C1 g1 C2 g2 )O h ...Composition formula (1A)

[0028] The above composition formula (1) and composition formula (1A) are equivalent, and the values ​​of the coefficients a to h in the above composition formula (1) are a+b+c+d1+d2=1, e is arbitrary, f1+f2+f3+g1+g2=1, and h is an arbitrary value that constitutes a perovskite structure. When element A contains two metal elements, the value of the coefficient d of element A is expressed as the sum of the coefficients d1 and d2 of the two elements A1 and A2. When element B contains three metal elements, the value of the coefficient f of element B is expressed as the sum of the coefficients f1, f2, and f3 of the three elements B1, B2, and B3. The same applies when element B contains four or more metal elements. When element C contains two metal elements, the value of the coefficient g of element C is expressed as the sum of the coefficients g1 and g2 of the two elements C1 and C2. The same applies when element C contains three or more metal elements.

[0029] In the above composition formula (1), K, Na, Li, and element A (Ca, Sr, Ba) are arranged in the so-called A site of the perovskite structure. Furthermore, element B (one or more of Nb, Ta, Ti, Zr, Hf, Sn, Sb, and Si, including at least Nb) and element C (one or more of Mg, Al, Sc, Mn, Fe, Co, Ni, Zn, Ga, and Y) are arranged in the so-called B site of the perovskite structure. Of the coefficients a, b, c, and d of the elements in the A site, it is preferable that the sum of a and b (a + b) is not zero, but coefficients c and d may be zero. Furthermore, of the coefficients f and g of elements D and E in the B site, it is preferable that the coefficient f of element D is not zero, but the coefficient g of element E may be zero. That is, the alkali niobate perovskite oxide of this embodiment is preferably a perovskite oxide that contains at least one or more alkali metals (K, Na, Li) and may also contain alkaline earth metals (Ca, Sr, Ba) at its A site, and that contains at least one of Nb, Ta, Ti, Zr, Hf, Sn, Sb, and Si, including at least Nb, and may also contain at least one other metal (Mg, Al, Sc, Mn, Fe, Co, Ni, Zn, Ga, Y) at its B site. Most preferably, the B site contains Nb.

[0030] As the values of the coefficients a to h in the above compositional formula (1), among the combinations of values that form a perovskite structure, preferred values can be selected from the perspective of the electrical properties or piezoelectric properties (especially the piezoelectric constant d 33 ) of the lead-free piezoelectric ceramic composition. Specifically, it is preferable that the coefficients a, b, and c are each values of 0 or more and less than 1, and a = b = c = 0 (that is, a lead-free piezoelectric ceramic composition that does not contain any of K, Na, and Li) does not hold. The coefficients a and b of K and Na are typically 0 < a ≤ 0.6 and 0 < b ≤ 0.6. The coefficient c of Li may be zero, but 0 < c ≤ 0.2 is preferable, and 0 < c ≤ 0.1 is more preferable. The coefficient d of the element A (one or more of Ca, Sr, Ba) may be zero, but 0 < d ≤ 0.2 is preferable, and 0 < d ≤ 0.1 is even more preferable. The coefficient e with respect to the entire A site is arbitrary, but 0.80 ≤ e ≤ 1.10 is preferable, 0.84 ≤ e ≤ 1.08 is even more preferable, and 0.88 ≤ e ≤ 1.07 is most preferable. The coefficient h of oxygen can take any value such that the main phase constitutes a perovskite-type oxide. A typical value of the coefficient h is about 3, and 3.0 ≤ h ≤ 3.1 is preferable. The value of the coefficient h can be calculated from the electrical neutrality condition of the composition of the main phase. However, as the composition of the main phase, a composition slightly deviating from the electrical neutrality condition is also acceptable.

[0031] Among the alkali niobate perovskite-type oxides represented by the above compositional formula (1), oxides having K, Na, and Nb as main metal components are referred to as "KNN" or "KNN material" and are excellent in piezoelectric properties, electrical properties, etc.

[0032] The lead-free piezoelectric ceramic composition of the present embodiment may have a secondary phase composed of another crystal phase in addition to the crystal phase of the alkali niobate perovskite-type oxide that is the main phase, as long as the object of the present invention is not impaired.

[0033] The subphase preferably contains an M-Ti-O spinel compound. The M-Ti-O spinel compound is mainly composed of a compound represented by the following composition formula (2). In this specification, the term "spinel compound" includes both normal spinel compounds having a normal spinel crystal structure and inverse spinel compounds having an inverse spinel crystal structure.

[0034] The M-Ti-O spinel compound is an oxide containing the element M and Ti (titanium), and is represented, for example, by the following composition formula (2).

[0035] M j TiO k ...Composition formula (2)

[0036] Here, the element M is a monovalent to tetravalent element, specifically, at least one element selected from the group consisting of Li, Mg, Al, Sc, Mn, Fe, Co, Ni, Zn, Ga, Y, and Zr.

[0037] The coefficients j and k are relative values ​​when the coefficient of Ti is set to 1. In order for the subphase to form a spinel-type compound, the coefficient j preferably satisfies 0.5≦j≦5.0. The coefficient k may be any value that forms a spinel compound, but preferably satisfies, for example, 2≦k≦8.

[0038] The second crystal phase composed of a spinel-type compound stabilizes the structure of the first crystal phase, resulting in a lead-free piezoelectric ceramic composition with excellent piezoelectric properties. From the viewpoint of piezoelectric properties, the M-Ti-O spinel-type compound is preferably one represented by the composition formula M2TiO4 or (M1,M2)TiO4, which contains two divalent elements M.

[0039] The alkali niobate perovskite oxide that constitutes the main phase is a material that is inherently prone to the formation of voids (void spaces), which are thought to be the cause of reduced piezoelectric properties, but the structure of the main phase is stabilized by filling the voids in the main phase with the subphase, and therefore the piezoelectric body made of the lead-free piezoelectric ceramic composition has excellent piezoelectric properties.

[0040] The lead-free piezoelectric ceramic composition may further contain, as a subphase, a crystalline phase other than the crystalline phase containing the M-Ti-O spinel compound, as long as the object of the present invention is not impaired. Even when the subphase further contains a crystalline phase other than the crystalline phase containing the M-Ti-O spinel compound, the subphase fills voids formed between the fine crystals of the main phase.

[0041] In this embodiment, the proportion of the subphase in the lead-free piezoelectric ceramic composition is not particularly limited as long as it does not impair the object of the present invention, but for example, it is preferably more than 0 vol% and not more than 10 vol%, and more preferably 0.5 vol% or more and 5 vol% or less.

[0042] If the Vmax of a piezoelectric vibrator during resonant driving is low, thermal runaway occurs during driving, causing a rapid temperature rise and significantly shortening the life of the piezoelectric vibrator. In order to suppress thermal runaway during resonant driving in a piezoelectric vibrator, it is necessary to increase the Vmax during resonant driving. The lead-free piezoelectric ceramic composition of this embodiment preferably has a critical vibration velocity (Vmax) of more than 0.7 m / s as a material.

[0043] Generally, the piezoelectric constant d of lead-free piezoelectric ceramics is 31 is the piezoelectric constant d of leaded piezoelectric ceramic 31 , which is smaller than . For this reason, in order to ensure that lead-free piezoelectric ceramics have the same vibration speed as leaded piezoelectric ceramics, a relatively high voltage is often required. Furthermore, in order to ensure the desired vibration speed of a piezoelectric vibrator, it is preferable that the mechanical quality factor Qm has a high value. The mechanical quality factor Qm indicates the sharpness of mechanical vibrations near the resonance frequency. In order to suppress heat generation in the piezoelectric vibrator during resonant driving, it is also preferable that the mechanical quality factor Qm has a high value. Furthermore, in order to resonantly drive a piezoelectric vibrator at a lower voltage, it is important to consider not only Qm but also d 31 Considering also, d 31 It is preferable that the value of d × Qm is high. It is also generally known that the value of Qm decreases when driven with a high load compared to when driven without a load. Therefore, in a piezoelectric vibrator that is handled by resonance driving, the value of d × Qm when driven with a high load is31 × Qm value is preferably high. 31 × Qm value, the vibration stress Tm = 20 MPa. 31 ×Qm value change rate Δ(d 31 × Qm), the smaller the vibration stress Tm is, the more stable the resonant driving of the piezoelectric vibrator becomes. The vibration stress Tm indicates the amplitude of the maximum stress at the center of the sample. The lead-free piezoelectric ceramic composition of this embodiment has a 31 It is preferable to realize a piezoelectric vibrator in which the value of Qm is lower than 76%.

[0044] <Method for producing lead-free piezoelectric ceramic composition> An example of a method for producing the lead-free piezoelectric ceramic composition having the above configuration will be described below.

[0045] (First component raw material mixing process) First, the raw materials for the first component necessary for forming the main phase are mixed. The first component is the main component contained in the main phase. The raw materials for the first component may be oxides, carbonates, or hydroxides of the elements contained in the main phase. The raw materials for the first component are selected from, for example, K2CO3 powder, Na2CO3 powder, Li2CO3 powder, CaCO3 powder, SrCO3 powder, BaCO3 powder, Nb2O5 powder, Ta2O5 powder, TiO2 powder, ZrO2 powder, MgO powder, Fe2O3 powder, CoO powder, ZnO powder, and Mn species (e.g., MnCO3, MnO, Mn2O3, MnO2, etc.). The selected raw material powders are weighed out to achieve the desired composition. Ethanol is added to the mixture of the weighed raw material powders, and the mixture is wet-mixed in a ball mill, preferably for 15 hours or more, to obtain a slurry.

[0046] (First component calcination step) The resulting slurry is dried, and the mixed powder obtained after drying is calcined in an air atmosphere at a temperature of 600°C to 1100°C for 1 hour to 10 hours to obtain a powdered calcined main phase product.

[0047] (Raw material mixing process for the second component) In addition, raw materials for the second component necessary for forming the subphase are mixed. The second component is a main component contained in the subphase. The raw materials for the second component may be oxides, carbonates, or hydroxides of the elements contained in the subphase. Multiple raw material powders are prepared and weighed to achieve the desired composition. The composition of the second component is preferably an M-Ti-O spinel compound. The composition of the second component may be Mn2TiO4, MnTi2O4, LiMnTiO4, etc. The raw materials for the second component are selected as needed from Li2CO3 powder, MnCO3 powder, TiO2 powder, etc., and weighed according to the value of the composition formula of the second component. Ethanol is added to the weighed raw material powders, and the mixture is wet-mixed in a ball mill, preferably for 15 hours or more, to obtain a slurry.

[0048] (Pre-baking step of second component) The obtained slurry is dried, and the mixed powder obtained after drying is calcined in an air atmosphere at a temperature of 600°C to 1100°C for 1 hour to 10 hours to obtain a powdered calcined subphase product.

[0049] (Mixing / molding process) Next, the obtained main phase calcined product and subphase calcined product are each weighed, and a dispersant, binder, and ethanol are added. The mixture is wet-mixed in a ball mill for preferably 15 hours or more to obtain a slurry. The wet-mixed slurry is passed through a mesh to remove coarse particles. The mesh opening is, for example, 250 μm. The slurry obtained after passing through the mesh is dried and then molded into the desired shape, for example, by uniaxial pressing at a pressure of 20 MPa. A compact is then obtained by, for example, CIP (cold isostatic pressing) at a pressure of 150 MPa. The obtained compact is then calcined in an air atmosphere at a temperature of 600°C to 800°C for 1 hour to 10 hours to remove the binder, thereby obtaining a compact that is a calcined product of the lead-free piezoelectric ceramic composition.

[0050] (Firing process) The resulting compact is fired in an air atmosphere at 900°C to 1300°C for 1 hour to 10 hours to obtain a lead-free piezoelectric ceramic as a fired body of the lead-free piezoelectric ceramic composition. After firing, the second component reacts with the first component and Mn oxide to form a subphase containing an M-Ti-O spinel compound such as Mn2TiO4, MnTi2O4, or LiMnTiO4. This firing may be carried out in an air atmosphere.

[0051] <Configuration of Piezoelectric Element 200> Next, a piezoelectric element 200 according to a first embodiment will be described with reference to FIG. 1. The piezoelectric element 200 includes a disk-shaped piezoelectric layer 100 and electrodes 301 and 302 attached to the upper and lower surfaces of the piezoelectric layer 100. The piezoelectric layer 100 is formed from the lead-free piezoelectric ceramic composition described above. The piezoelectric layer 100 is polarized in the thickness direction. The electrodes 301 and 302 are made of, for example, Au.

[0052] <Method of manufacturing the piezoelectric element 200> (Processing process) The above-mentioned lead-free piezoelectric ceramic is processed in accordance with the dimensional accuracy required for the piezoelectric element 200 .

[0053] (Electrode attachment process) After polishing both the front and back surfaces of the processed lead-free piezoelectric ceramic, electrodes 301 and 302 made of Au are formed by, for example, sputtering, and then annealing is carried out at 400°C.

[0054] (Polarization process) After the electrodes 301 and 302 are formed, the lead-free piezoelectric ceramic is subjected to a polarization process, for example, by applying a DC voltage of 5 kv / mm in silicone oil at 50°C, thereby causing the lead-free piezoelectric ceramic to exhibit the piezoelectric properties of the piezoelectric layer 100. In this way, the piezoelectric element 200 is obtained.

[0055] <Configuration of Piezoelectric Element 10> Next, a piezoelectric element 10 according to a second embodiment will be described with reference to FIG. 2. FIG. 2 is a cross-sectional view of the piezoelectric element 10. As shown in FIG. 2, the piezoelectric element 10 includes a piezoelectric layer 11, a plurality of internal electrodes 12 and 13 in contact with the piezoelectric layer 11, and two external electrodes 14 and 15 connected to the internal electrodes 12 and 13. The piezoelectric layer 11 is formed from the lead-free piezoelectric ceramic described above. The internal electrodes 12 and 13 are primarily composed of a base metal. The piezoelectric layer 11 and the internal electrodes 12 and 13 are alternately stacked. More specifically, the piezoelectric layer 11 and the internal electrodes 12 and 13 are stacked in the following order: piezoelectric layer 11, internal electrode 12, piezoelectric layer 11, internal electrode 13, piezoelectric layer 11, etc., with one piezoelectric layer 11 sandwiched between the two internal electrodes 12 and 13. The two external electrodes 14 and 15 are disposed on the outer surfaces of the laminate of the piezoelectric layer 11 and the internal electrodes 12 and 13. The external electrodes 14, 15 are mainly composed of Au, for example. One end of one of the two internal electrodes 12, 13 in contact with one piezoelectric layer 11 is connected to one external electrode 14, and one end of the other internal electrode 13 is connected to the other external electrode 15. When a voltage is applied between the external electrodes 14, 15, the piezoelectric layer 11 expands and contracts, and the entire piezoelectric element 10 expands and contracts.

[0056] <Method of manufacturing the piezoelectric element 10> In the mixing and molding process of the lead-free piezoelectric ceramic composition, the slurry obtained by passing it through a mesh is processed into a sheet shape using a doctor blade method or the like to produce a ceramic green sheet, which is an example of a molded body of the lead-free piezoelectric ceramic composition.

[0057] (Electrode layer formation process) An electrode layer that will become an internal electrode is formed on one side of a ceramic green sheet using a conductive paste for the internal electrode, for example, by screen printing. The electrode layer is primarily composed of, for example, Pd, Ag, Pt, Cu, or Ni. Then, multiple ceramic green sheets with electrode layers formed thereon are stacked so that the electrode layers are exposed alternately on both sides, and ceramic green sheets without electrode layers are further stacked on both sides of the stack. The resulting stack is then pressed together to obtain a laminate in which ceramic green sheets and electrode layers are alternately stacked. After cutting this stack into a desired shape, the laminate is subjected to a binder removal process, for example, by holding it at a temperature of 200°C to 400°C for 2 hours to 10 hours.

[0058] (Firing process) The laminate after the binder removal treatment is fired at a temperature of 900° C. or higher and 1300° C. or lower for 1 hour or higher and 10 hours or lower.

[0059] (Electrode attachment process) After the fired laminate is polished on its outer surface, the external electrodes 14 and 15 made of Au are formed by, for example, sputtering, followed by annealing at 400°C.

[0060] (Polarization process) After the external electrodes 14, 15 are formed, the laminate is subjected to the polarization treatment of the first embodiment, thereby causing the lead-free piezoelectric ceramic to exhibit the piezoelectric properties of the piezoelectric layer 11. In this way, the piezoelectric element 10 is obtained.

[0061] The manufacturing methods of the first and second embodiments described above are merely examples, and various other steps and processing conditions for manufacturing piezoelectric elements can be adopted. For example, instead of separately producing the main phase and subphase calcined products and then mixing and firing the powders of the two, it is also possible to mix the raw materials in a ratio appropriate for the final composition of the lead-free piezoelectric ceramic and then fire the mixture. Furthermore, metals or alloys such as platinum (Pt), silver-palladium (Ag-Pd), and silver (Ag) can also be used as the electrode material.

[0062] <Application examples of piezoelectric elements> The piezoelectric element of the present disclosure can be widely used for vibration detection, pressure detection, oscillation, piezoelectric device applications, etc. Specifically, the piezoelectric elements 10 and 200 are suitable for use in the following devices: ultrasonic scalpels, ultrasonic scalers, ultrasonic cleaners, ultrasonic processing machines, piezoelectric transducers, ultrasonic motors, piezoelectric gyro sensors, piezoelectric filters, knock sensors, etc.

[0063] (ultrasonic scalpel) 3 is a schematic diagram of an ultrasonic scalpel 110, which is an example of a device equipped with a piezoelectric element according to the present disclosure. The ultrasonic scalpel 110 includes an ultrasonic vibrator 111 and an operating member 113. The ultrasonic vibrator 111 has the above-described piezoelectric element 200, and is driven to generate ultrasonic vibrations when an electrical signal is applied. The ultrasonic vibrator 111 operates to transmit ultrasonic vibrations to the operating member 113, which is configured in a shaft shape. The ultrasonic vibrator 111 drives the operating member 113 so as to perform an incision, ablation, or thermal coagulation hemostasis on biological tissue in the vicinity of the operating member 113.

[0064] (Ultrasonic Scaler) 4 is a schematic diagram of an ultrasonic scaler 120, an example of a device equipped with the piezoelectric element of the present disclosure. The ultrasonic scaler 120 includes an ultrasonic vibrator 121 and a dental tip 122. The ultrasonic vibrator 121 has the above-described piezoelectric element 200 and is driven to generate ultrasonic vibrations when an electrical signal is applied. The ultrasonic vibrator 121 operates to transmit the ultrasonic vibrations to the dental tip 122.

[0065] (ultrasonic cleaner) 5 is a schematic diagram of an ultrasonic cleaner 130, which is an example of an apparatus equipped with the piezoelectric element of the present disclosure. The ultrasonic cleaner 130 includes an ultrasonic vibrator 131 and a cleaning container 133. The ultrasonic vibrator 131 has the above-described piezoelectric element 200, and is driven to generate ultrasonic vibrations when an electric signal is applied. An object 135 to be cleaned is placed in the cleaning container 133 containing a cleaning liquid, and the ultrasonic vibrator 131 is vibrated to generate ultrasonic vibrations, which are transmitted to the cleaning liquid, thereby cleaning the object 135 to be cleaned.

[0066] (Ultrasonic processing machine) FIG. 6 is a schematic diagram of an ultrasonic processing machine 140, an example of a device equipped with a piezoelectric element according to the present disclosure. The ultrasonic processing machine 140 includes a substrate 141, an ultrasonic vibrator 143, a grinding stone 145, and a spindle 147. The substrate 141 is disk-shaped, and the grinding stone 145 is formed on its outer periphery. The center of the substrate 141 is fixed to the spindle 147. The ultrasonic vibrator 143 includes the piezoelectric element 200 described above, and is driven to generate ultrasonic vibrations when an electrical signal is applied. The driving direction of the ultrasonic vibrator 143 is the radial direction from the center of the substrate 141 to the outer periphery. While the ultrasonic vibrator 143 generates vibrations, the spindle 147 is rotated about its axis, and the grinding stone 145 formed on the outer periphery of the substrate 141 is pressed against the workpiece, thereby cutting the workpiece.

[0067] (piezoelectric transducer) 7 is a schematic diagram of a piezoelectric transducer 150, which is an example of a device including a piezoelectric element according to the present disclosure. The piezoelectric transducer 150 includes a piezoelectric element 151. The piezoelectric element 151 has a configuration similar to that of the piezoelectric element 200 described above. The piezoelectric element 151 includes a piezoelectric layer 156 and electrodes 155 and 157 attached to both sides of the piezoelectric layer 156.

[0068] (ultrasonic motor) 8 is a schematic diagram of an ultrasonic motor 160, which is an example of a device equipped with the piezoelectric element of the present disclosure. The ultrasonic motor 160 includes an ultrasonic vibrator 161, a rotor 163, and an output shaft 165. The ultrasonic vibrator 161 has the above-described piezoelectric element 200. For example, when an AC voltage is applied to the piezoelectric element, a bending traveling wave is generated in the ultrasonic vibrator 161, and each point on the sliding surface of the ultrasonic vibrator 161 performs an elliptical motion. When the rotor 163 is pressed against the sliding surface of the ultrasonic vibrator 161, the rotor 163 receives a frictional force from the ultrasonic vibrator 161 and rotates in the opposite direction to the bending traveling wave.

[0069] (Piezoelectric gyro sensor) 9 schematically illustrates a piezoelectric gyro sensor 170, which is an example of a device including the piezoelectric element of the present disclosure. The piezoelectric gyro sensor 170 includes a piezoelectric layer 171 and a piezoelectric element 177 including electrodes 173 and 175 applied to both sides of the piezoelectric layer 171. The piezoelectric element 177 has a configuration similar to that of the piezoelectric element 200 described above.

[0070] (Piezoelectric filter) 10 schematically illustrates a piezoelectric filter 180, which is an example of a device including a piezoelectric element according to the present disclosure. The laminated piezoelectric filter 180 includes a plate-shaped piezoelectric layer 181 and a piezoelectric element 187 having electrodes 183 and 185 on both sides of the piezoelectric layer 181. The piezoelectric element 187 has a configuration similar to that of the piezoelectric element 200 described above.

[0071] (knock sensor) 11 schematically illustrates a knock sensor 190, which is an example of a device including a piezoelectric element according to the present disclosure. Knock sensor 190 includes a piezoelectric element 197 including a piezoelectric layer 191 and electrodes 193 and 195. Piezoelectric element 197 has a configuration similar to that of piezoelectric element 200 described above.

[0072] The piezoelectric element of the present disclosure is particularly suitable for use in devices that require thermal durability. [Example]

[0073] The present invention will be described in more detail below based on examples, but the present disclosure is not limited to these examples in any way.

[0074] <Examples 1 to 4> In the raw material mixing step for the first component, K2CO3 powder, Na2CO3 powder, Li2CO3 powder, CaCO3 powder, BaCO3 powder, Nb2O5 powder, TiO2 powder, MnCO3 powder, Fe2O3 powder, and MgO powder were prepared as raw material powders. The prepared raw material powders were weighed out so that the coefficients in the composition formula of the first component were in the quantitative ratios shown in Figure 12. Ethanol was added to the mixture of the weighed raw material powders, and the mixture was wet-mixed in a ball mill for 15 hours or more to obtain a slurry.

[0075] The obtained slurry was dried in a calcination step for the first component, and the mixed powder obtained after drying was calcined in an air atmosphere at a temperature condition of 600°C to 1000°C for 1 hour to 10 hours to obtain a powdered calcined main phase product. As shown in FIG. 12, Examples 1 to 4 are all KNN materials containing K, Na, and Nb as main components. Example 1 and Example 2 have the same composition. Example 3 differs slightly from Examples 1 and 2 in the quantitative ratios of Nb, Ti, and Mn. Examples 1, 2, and 3 contain Mn in their compositions. Example 4 does not contain Mn in its composition, but contains Fe and Mg.

[0076] In the raw material mixing step for the second component, MnCO3 powder and TiO2 powder were prepared as raw material powders for the M-Ti-O spinel-type compound represented by the composition formula (3) above. Each of these raw material powders was weighed according to the values ​​of the coefficients j and k in the composition formula (2) above. An appropriate amount of ethanol was added to the mixture of the weighed raw material powders, and the mixture was wet-mixed using a ball mill for 15 hours to obtain a slurry. In the calcination step for the second component, the obtained slurry was dried, and the mixed powder obtained after drying was calcined in an air atmosphere at a temperature of 600°C to 1100°C for 1 hour to 10 hours to obtain a powdered calcined subphase product.

[0077] In the mixing and forming step, the obtained main phase calcined product and subphase calcined product were each weighed, and a dispersant, binder, and ethanol were added. The mixture was wet-mixed in a ball mill for 15 hours or more to obtain a slurry. The wet-mixed slurry was passed through a mesh to remove coarse particles. The slurry obtained after passing through the mesh was dried and then uniaxially pressed at a pressure of 20 MPa, for example, to form it into the desired shape. A CIP (cold isostatic pressing) process was then performed at a pressure of 150 MPa, for example, to obtain a green body. The obtained green body was subjected to a binder removal process by calcining it in an air atmosphere at a temperature of 600°C to 800°C for 1 hour to 10 hours, to obtain a green body that was a calcined product of the lead-free piezoelectric ceramic composition.

[0078] The resulting compacts were fired in a firing step under the firing conditions shown in Fig. 12 to obtain lead-free piezoelectric ceramics as fired bodies of the lead-free piezoelectric ceramic compositions. As shown in Fig. 12, the firing conditions for Examples 1 and 3 were a temperature of 1140°C and holding time of 1 hour, and the firing conditions for Examples 2 and 4 were a temperature of 1150°C and holding time of 10 hours.

[0079] The obtained lead-free piezoelectric ceramics of Examples 1 to 4 were cut with a dicer into shapes of length X: 12 mm × width Y: 3 mm × thickness Z: 1 mm for evaluation of piezoelectric properties. The cut samples were subjected to polarization treatment in the thickness direction using an oil bath or the like at a temperature of 50°C and an electric field strength of 5 kV / mm for 30 minutes.

[0080] <Comparative Example 1> A sample of lead-containing piezoelectric ceramic containing lead zirconate titanate (so-called PZT) as a main component was produced as Comparative Example 1. The lead-containing piezoelectric ceramic of Comparative Example 1 was made of (Pb r-x E x )(Ti y Zr 1-y )O3, and Pb(N1 s N2 t)O3, where the element E is at least one element selected from the group consisting of Ca, Sr, Ba, and rare earth elements including Bi, La, etc. The coefficients r, x, and y satisfy 0.96≦r≦1.03, 0≦x≦0.2, and 0.3≦y≦0.7. N1 is at least one metal element selected from the group consisting of Mg, Ni, Y, Fe, Yb, Sc, Y, Co, Ho, In, Lu, Sb, Er, and Mn. N2 is at least one metal element selected from the group consisting of Ta, Nb, Sb, and W. s and t satisfy s+t=1.

[0081] PbO powder, SrO powder, ZrO powder, TiO powder, NbO powder, and MnCO powder were prepared as raw material powders for the main and subcomponents of the leaded piezoelectric ceramic composition of Comparative Example 1. The prepared raw material powders were weighed so that the coefficients in the composition formulas of the main and subcomponents were in the quantitative ratios shown in FIG. 13. Ethanol was added to a mixture of the weighed raw material powders and mixed in a ball mill to obtain a mixed powder. The resulting mixed powder was calcined at 900°C for 2 hours to obtain a powdered calcined product. The calcined powder was pulverized in a ball mill and sized using a particle size distribution analyzer to have an average particle size (median diameter) of 0.4 μm. A dispersant and a binder were added to this powder, mixed, granulated, and then molded into a disk with a diameter of 30 mm and a thickness of 4 mm at a molding pressure of 98 kPa. The molded body was fired at a temperature of 900°C to 1200°C to obtain a disk-shaped fired body. The obtained fired body, the leaded piezoelectric ceramic of Comparative Example 1, was cut into the same shape as in Examples 1 to 4 for evaluation of piezoelectric properties. The cut samples were subjected to the same polarization treatment as in Examples 1 to 4.

[0082] <Sample evaluation> (Evaluation of vibration velocity) Each sample was resonantly driven by applying an AC voltage generated by a function generator to the sample in 33 directions. The function generator used was a Keysight Technologies, Inc. 33500B function generator. The vibration velocity of each sample in 31 directions during resonant driving was measured using a laser Doppler vibrometer, and the vibration velocity values ​​were read using an oscilloscope. The laser Doppler vibrometer used was a compact laser Doppler vibrometer NLV-2500 manufactured by Shinkawa Electric Co., Ltd. The oscilloscope used was a mixed signal oscilloscope DLM5034 manufactured by Yokogawa Measurement Corporation. Furthermore, the temperature rise at the vibration node of the vibrator during resonant driving was measured using a K-type thermocouple, and the measured values ​​were read on a personal computer (PC) using a thermocouple measurement device. The thermocouple measurement device used was a National Instruments Japan USB-TC01 thermocouple measurement device. The relationship between vibration velocity and heat generation during resonant driving of the samples of Examples 1 to 4 and Comparative Example 1, as measured, is shown in Figure 14. The critical vibration velocity Vmax [m / s] is the vibration velocity at which the temperature rise at the vibration node of the vibrator reaches 20°C while being resonantly driven at room temperature. Vmax for each sample, obtained from the relationship shown in Figure 14, is shown in Figure 15.

[0083] (Evaluation of piezoelectric properties under high load) Piezoelectric constant d 31 and mechanical quality factor Qm multiplied by d 31 Each sample was evaluated based on the value of d × Qm. 31 × d under high load when the vibration stress Tm at the center of the vibrator is 20 MPa for the value of Qm 31 ×Qm value change rate Δ(d 31Each sample was evaluated based on the value of (Qm × Qm). This evaluation was performed using the electrical transient response method described in the literature by Mikio Umeda et al. 1998 Jpn. J. Appl. Phys. 37 5322. The electrical transient response method involves applying a voltage close to the resonant frequency to a vibrator made of piezoelectric material, and achieving a large amplitude state through burst driving, which is a short-term drive until vibration is excited. After that, the vibration velocity and current decay waveforms under electrical terminal short circuit are used to evaluate the characteristics at any vibration level. Before the transient response measurement, the resonant frequency fr [Hz], which is the instantaneous frequency of the vibration velocity, and the piezoelectric constant d 31 [pC / N], mechanical quality factor Qm at resonant drive, elastic compliance s 11 E [pm 2 / N] were measured by the resonance-antiresonance method in accordance with the Electronic Materials Industries Association of Japan standard (EMAS-6100).

[0084] Measurements using the electrical transient response method were performed using an equipment configuration consisting of a function generator, power amplifier, laser Doppler vibrometer, a specified current probe, and an oscilloscope. The function generator and laser Doppler vibrometer were as described above. The power amplifier used was a bipolar amplifier HAS 4052 manufactured by NF Corporation. The oscilloscope used was a mixed signal oscilloscope DLM3034 manufactured by Yokogawa Measurement Corporation.

[0085] Using this device configuration, a burst wave of 100 Vpp to 200 Vpp, which is a frequency near the resonant frequency of each sample between 100 kHz and 300 kHz, was applied to each sample, and each sample was burst-driven at a high vibration level. The drive voltage was then set to 0 V, i.e., the electrical terminals were short-circuited. After the electrical terminals were short-circuited, the vibration velocity attenuated over time while vibrating at the resonant frequency fr. In this way, the vibration velocity and current decay waveforms immediately after the end of voltage application were obtained for each sample. The obtained decay waveforms were analyzed using general-purpose waveform analysis software to determine the instantaneous amplitude I [A] of the current from the high vibration level to the low vibration level, the instantaneous amplitude V [m / s] of the vibration velocity, the resonant frequency fr [Hz] which is the instantaneous frequency of the vibration velocity, and the damping constant β [s -1 Using the obtained measurement data, the equivalent mechanical quality factor Qm and the equivalent vibration stress Tm [MPa] were calculated using the following formulas.

[0086]

number

[0087] In the above formulas (1) to (5), X represents the length of the sample, Y represents the width of the sample, ρ represents the density of the sample, and A represents the force constant. Based on formulas (1) to (5), the equivalent mechanical quality factor Qm and the equivalent elastic compliance s 11 E , equivalent piezoelectric constant d 31 , and the equivalent vibration stress Tm are calculated. "Equivalent" means that the Qm,s calculated by the electrical transient response method 11 E ,d 31 ,Tm. These equivalent Qm,s 11 E ,d 31 ,Tm are calculated based on the main constants Qm,s 11 E ,d 31 , Tm are basically the same physical constants.

[0088] In this embodiment, the vibration stress is defined as being under high load when the equivalent vibration stress Tm is 20 MPa. The equivalent piezoelectric constant d 31 and d based on the value of the equivalent mechanical quality factor Qm 31 × Qm is calculated by multiplying the value of d 31 ×Qm. Also, d measured in advance by the resonance-antiresonance method 31 and d based on the value of Qm 31 × Qm is the value of d when the vibration stress is unloaded. 31 For each sample, the vibration stress is defined as d 31 × d at high load for the value of Qm 31 ×Qm value change rate Δ(d 31 × Qm) was calculated. 31 × Qm) is the value of d when the vibration stress is unloaded 31 From the value of ×Qm, d at high load 31 × Qm value. 31 × Qm) are shown in FIG.

[0089] As shown in FIG. 14, the temperature rise was measured for each sample of Examples 1 to 4 and Comparative Example 1 when resonant driving was started from room temperature of about 20°C. As a result, the Vmax of each of Examples 1 to 4 relating to the lead-free piezoelectric ceramic was higher than the Vmax of Comparative Example 1 relating to the lead-containing piezoelectric ceramic.

[0090] Specifically, as shown in FIG. 15 , the Vmax of all of Examples 1 to 4 was higher than the Vmax of Comparative Example 1, which was 0.7 m / s. Of the Vmax of Examples 1 to 4, the Vmax of Example 4 was the lowest, at 0.8 m / s. That is, the Vmax of the samples according to the lead-free piezoelectric ceramic composition of this embodiment was 0.8 m / s or higher. Specifically, Examples 1 to 3, in which Mn was included in the composition of the main phase of the lead-free piezoelectric ceramic composition, had higher Vmax values ​​than Example 4, in which Mn was not included in the composition of the main phase of the lead-free piezoelectric ceramic composition but Fe and Mg were included. Furthermore, of Examples 1 to 3, the Vmax of Examples 1 and 3, in which the firing conditions in the firing step were a temperature of 1140°C and holding for 1 hour, was 0.9 m / s and 1 m / s, respectively. The Vmax of Example 2, in which the firing conditions in the firing step were a temperature of 1150°C and holding time of 10 hours, was 1.1 m / s, which was higher than the Vmax of each of Examples 1 and 3. As described above, the Vmax of all the samples related to the lead-free piezoelectric ceramic composition of this embodiment was higher than the Vmax of the sample of the lead-containing piezoelectric ceramic composition of Comparative Example 1. Therefore, it was clear that by using the lead-free piezoelectric ceramic composition of this embodiment, the life of the piezoelectric vibrator can be extended more than by using the lead-containing piezoelectric ceramic composition of Comparative Example 1.

[0091] As shown in FIG. 15, the Δ(d 31 × Qm) was 76%. That is, in Comparative Example 1, the vibration stress was d 31 × Qm value, d at Tm = 20 MPa, where the vibration stress is high load 31 On the other hand, the value of each Δ(d 31 × Qm) are all the same as those of Comparative Example 1. 31 ×Qm) and satisfied at least 70% or less. In detail, among Examples 1 to 4, Example 2, in which Mn was contained in the composition of the main phase of the lead-free piezoelectric ceramic composition and the firing conditions in the firing step were a temperature of 1150°C and holding for 10 hours, showed a Δ(d 31 Next, the Δ(d × Qm) of Examples 1 and 3, in which Mn was included in the composition of the main phase of the lead-free piezoelectric ceramic composition and the firing conditions of the firing step were a temperature of 1140°C and holding time of 1 hour, was the lowest.31 The Δ(d × Qm) of Example 4, in which the main phase of the lead-free piezoelectric ceramic composition did not contain Mn but contained Fe and Mg, and the firing conditions of the firing step were a temperature of 1150°C and holding time of 10 hours, were 43% and 50%, respectively. 31 From these evaluation results, it can be seen that the lead-free piezoelectric ceramic compositions according to Examples 1 to 4 have a smaller Δ(d 31 It has become clear that it is possible to provide a piezoelectric vibrator that has a small value of Qm and can perform stable resonant driving. [Explanation of symbols]

[0092] 10,151,177,187,197,200: Piezoelectric element 11, 156, 171, 181, 191: Piezoelectric layers 12, 13, 100: Internal electrodes 14,15: External electrode 155,157,173,175,183,185, 193,195,301,302: Electrode

Claims

1. A lead-free piezoelectric ceramic composition containing an alkali niobate perovskite oxide, When the temperature rise at the vibration node of the vibrator reaches 20°C while it is resonantly driven as a piezoelectric vibrator at room temperature, the vibration velocity is defined as the limit vibration velocity (Vmax). A lead-free piezoelectric ceramic composition characterized in that the critical vibration velocity (Vmax) is 0.8 m / s or more.

2. When vibration stress is unloaded, ３１ × d when vibration stress is high load (Tm = 20 MPa) for the value of Qm ３１ × Qm value change rate Δ(d ３１ 2. The lead-free piezoelectric ceramic composition according to claim 1, wherein the ratio of Qm to Qm (%) is 70 or less.

3. a main phase containing the alkali niobate perovskite oxide; 3. The lead-free piezoelectric ceramic composition according to claim 1, further comprising a subphase containing an M-Ti-O based spinel compound.

4. A piezoelectric element comprising a piezoelectric layer formed from the lead-free piezoelectric ceramic composition according to claim 1 or 2, and an electrode in contact with the piezoelectric layer.

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

6. 6. The device according to claim 5, which is selected from the group consisting 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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