Lead-free piezoelectric composition and piezoelectric element

Abstract

A lead-free piezoelectric composition according to the present invention comprises a main phase containing an alkali niobate perovskite oxide, and a sub-phase containing a Mn-Ti-O oxide, the maximum particle diameter of the Mn-Ti-O oxide in the sub-phase being 35 μm or less, and the number-based cumulative 80% particle size (D80) being 32 μm or less.

Description

[Technical field]

[0001] The present invention relates to a lead-free piezoelectric composition and a piezoelectric element. [Background technology]

[0002] Conventionally, most piezoelectric elements are made of PZT (lead zirconate titanate)-based materials. However, the lead contained in PZT is viewed as a problem because it causes environmental load, and in recent years, development of piezoelectric elements made of lead-free materials has been progressing.

[0003] As this type of lead-free material, for example, a lead-free piezoelectric composition has been proposed that has a main phase formed of a first crystal phase made of an alkali niobate-based perovskite-type oxide and a subphase containing a second crystal made of an M-Ti-O-based spinel compound (element M is a monovalent to tetravalent element) (see Patent Document 1).

[0004] Although the alkali niobate perovskite oxide constituting the main phase is originally a material that is prone to the formation of voids that cause a decrease in piezoelectric properties, the structure of the main phase (first crystal phase) is stabilized by filling the voids in the main phase with a subphase containing a second crystal. Therefore, the lead-free piezoelectric composition has excellent piezoelectric properties. In other words, when a force is applied to the lead-free piezoelectric composition, a voltage is generated, and when a voltage is applied, the lead-free piezoelectric composition expands and contracts in dimensions and changes in shape. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5715309

[0006] (Problem to be solved by the invention) Although the above-mentioned lead-free piezoelectric composition has excellent piezoelectric properties, it has a low dielectric breakdown voltage and therefore has a problem with insulation properties. Summary of the Invention

[0007] An object of the present invention is to provide a lead-free piezoelectric composition and the like which have excellent piezoelectric properties and excellent insulating properties.

[0008] (Means for solving the problem) The means for solving the above problems are as follows. <1> A lead-free piezoelectric composition having a main phase containing an alkali niobate-based perovskite-type oxide and a subphase containing a Mn-Ti-O-based oxide, wherein the maximum particle size of the Mn-Ti-O-based oxide in the subphase is 35 μm or less and the number-based cumulative 80% particle size (D80) is 32 μm or less.

[0009] <2> The average grain size of the Mn-Ti-O oxide in the subphase is 24 μm or less. <1> The lead-free piezoelectric composition according to claim 1.

[0010] <3> The Mn-Ti-O-based oxide is MnTi2O4 or the above-mentioned oxide containing Mn2TiO4. <1> or <2> The lead-free piezoelectric composition according to claim 1.

[0011] <4> The above <1> ~ <3> 3. A piezoelectric element comprising a laminate of a piezoelectric ceramic layer formed from the lead-free piezoelectric composition according to any one of claims 2 to 3 and an electrode attached to the piezoelectric ceramic layer.

[0012] (Effects of the Invention) According to the present invention, it is possible to provide a lead-free piezoelectric composition having excellent piezoelectric properties and excellent insulating properties. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a perspective view of a piezoelectric element according to a first embodiment; [Diagram 2] 1 is a cross-sectional view of a piezoelectric element according to a second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The lead-free piezoelectric composition and the piezoelectric element according to the embodiment will be described below.

[0015] The lead-free piezoelectric composition has a main phase containing an alkali niobate-based perovskite-type oxide and a sub-phase containing an Mn-Ti-O-based oxide.

[0016] The main phase is formed of a first crystal phase composed of an alkali niobate-based perovskite-type oxide. The alkali niobate-based perovskite-type oxide is represented by the following composition formula (1).

[0017] (A1 a M1 b ) c (Nb d1 Mn d2 Ti d3 Zr d4 )O 3+e ···(1)

[0018] The element A1 is at least one of the alkali metals Li, Na, and K. The element M1 is at least one of the alkaline earth metals Ba (barium), Ca (calcium), and Sr (strontium).

[0019] In the above composition formula (1), the element A1 and the element M1 are arranged at the A site of the perovskite structure, and Nb (niobium), Mn (manganese), Ti (titanium), and Zr (zirconium) are arranged at the B site.

[0020] As the values of the coefficients a to e in the above composition formula (1), among the values for which the perovskite structure is established, preferable values are selected from the viewpoint of the electrical properties or piezoelectric properties (particularly the piezoelectric constant d 33 ) of the lead-free piezoelectric composition.

[0021] Specifically, the coefficients a and b satisfy 0 < a < 1, 0 < b < 1, and a + b = 1, and a = 0 (i.e., a composition containing no alkali metal) and b = 0 (i.e., a composition containing none of Ba, Ca, and Sr) are excluded.

[0022] The coefficient c for the entire site A satisfies 0.80 < c < 1.10, preferably 0.84 ≤ c ≤ 1.08, and more preferably 0.88 ≤ c ≤ 1.07.

[0023] The coefficients d1, d2, d3, and d4 satisfy 0 < d1 < 1, 0 < d2 < 1, 0 < d3 < 1, 0 ≤ d4 < 1, and d1 + d2 + d3 + d4 = 1. The cases where d1 = 0 (composition without Nb), d2 = 0 (composition without Mn), and d3 = 0 (composition without Ti) are excluded. The coefficient d4 of Zr may be zero (i.e., the composition may not contain Zr).

[0024] Among the coefficients 3 + e of oxygen, the coefficient e is a positive or negative value indicating oxygen deficiency or excess with respect to the coefficient of oxygen, which is usually 3. The coefficient 3 + e of oxygen can take a value such that the main phase constitutes a perovskite-type oxide. A typical value of the coefficient e is e = 0, and 0 ≤ e ≤ 0.1 is preferred. Note that the value of the coefficient e can be calculated from the electrical neutrality condition of the composition of the main phase. However, as the composition of the main phase, a composition slightly deviated from the electrical neutrality condition is also acceptable.

[0025] Among the alkali niobate perovskite-type oxides represented by the above composition formula (1), the oxides having K, Na, and Nb as the main metal components are referred to as "KNN" or "KNN material" and are excellent in piezoelectric properties, electrical properties, etc.

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

[0027] (K a1 Na a2 Li a3 Ca b1 Sr b2 Ba b3 ) c (Nb d1 Mn d2 Ti d3 Zr d4 )O 3+e ···(1A)

[0028] The above compositional formula (1) and compositional formula (1A) are equivalent, where a1 + a2 + a3 = a and b1 + b2 + b3 = b. The coefficient a1 of K satisfies 0 < a1 ≤ 0.6, and the coefficient a2 of Na satisfies 0 < a1 ≤ 0.6. The coefficient a3 of Li satisfies 0 ≤ a3 ≤ 0.2 (preferably, 0 ≤ a3 ≤ 0.1).

[0029] The secondary phase is formed of a second crystal phase containing an Mn-Ti-O-based oxide. The Mn-Ti-O-based oxide is an oxide containing Mn (manganese) and Ti (titanium), and is represented by, for example, the following compositional formula (2).

[0030] MnTiO y ···(2)

[0031] The coefficient y satisfies 2 ≤ y ≤ 8.

[0032] Also, the Mn-Ti-O-based oxide may be MnTi2O4.

[0033] Also, the Mn-Ti-O-based oxide may be Mn2TiO4.

[0034] Note that the composition of Mn or Ti in the Mn-Ti-O-based oxide (for example, MnTi2O4, Mn2TiO4) may deviate within the range of ±0.2 from the desired value.

[0035] The lead-free piezoelectric composition of the present embodiment may contain other crystal phases (such as a third crystal phase, etc.) other than the second crystal phase as long as the object of the present invention is not impaired.

[0036] In the lead-free piezoelectric composition of the present embodiment, the maximum particle size of the Mn-Ti-O-based oxide in the secondary phase is 35 μm or less. The method for measuring the maximum particle size of the Mn-Ti-O-based oxide will be described later.

[0037] Also, in the lead-free piezoelectric composition of the present embodiment, the cumulative 80% particle size (D80) based on the number of particles of the Mn-Ti-O-based oxide in the secondary phase is 32 μm or less. The method for measuring the cumulative 80% particle size (D80) based on the number of particles will be described later.

[0038] When the maximum particle size of the Mn-Ti-O-based oxide in the subphase and the number-based cumulative 80% particle size (D80) of the Mn-Ti-O-based oxide in the subphase are within the above-mentioned ranges, a lead-free piezoelectric composition having excellent piezoelectric properties and excellent insulating properties (i.e., a high dielectric breakdown voltage) can be obtained.

[0039] In the lead-free piezoelectric composition of the present embodiment, the average particle size of the Mn-Ti-O oxide in the subphase is preferably 24 μm or less. The method for measuring the average particle size of the Mn-Ti-O oxide will be described later.

[0040] When the average particle size of the Mn-Ti-O based oxide in the subphase is within the above range, the piezoelectric characteristics and insulating properties of the lead-free piezoelectric composition are easily improved.

[0041] The subphase, which includes the second crystal phase that satisfies the above-mentioned conditions, is arranged in a scattered manner within the main phase, which is made of the first crystal phase. The subphase fills the voids (gaps) formed between the fine crystals of the main phase. Although the subphase does not have piezoelectric properties, its presence in the main phase improves the sinterability and structural stability of the lead-free piezoelectric composition, as well as the insulating properties.

[0042] In this embodiment, the ratio of the subphase contained in the lead-free piezoelectric composition is not particularly limited as long as it does not impair the object of the present invention, but is preferably, for example, 0.5 volume % or more and 5 volume % or less.

[0043] Next, a piezoelectric element 200 according to embodiment 1 will be described with reference to Fig. 1. Fig. 1 is a perspective view of the piezoelectric element 200 according to embodiment 1. As shown in Fig. 1, the piezoelectric element 200 according to this embodiment has a disk-shaped appearance and includes a disk-shaped piezoelectric layer (an example of a piezoelectric ceramic layer) 100 and electrodes 301, 302 attached to the upper and lower surfaces of the piezoelectric layer 100. The piezoelectric layer 100 is formed from the above-mentioned lead-free piezoelectric composition. The piezoelectric layer 100 is polarized in the thickness direction. The electrodes 301, 302 are made of, for example, Au.

[0044] Here, an example of a method for manufacturing the piezoelectric element 200 according to the first embodiment will be described. First, a plurality of kinds of raw material powders necessary for forming the main phase are prepared, and the raw material powders are weighed to obtain a target composition. The raw material powders may be oxides, carbonates, hydroxides, etc. of the elements contained in the main phase. Ethanol is added to a mixture of the weighed raw material powders, and the mixture is wet-mixed using a ball mill, preferably for 15 hours or more, to obtain a slurry. The obtained slurry is dried, and the mixed powder obtained after drying is calcined, for example, in an air atmosphere at a temperature condition of 600 to 1000° C. for 1 to 10 hours to obtain a powdered calcined product of the main phase.

[0045] In addition, a plurality of kinds of raw material powders necessary for forming the subphase are prepared, and the raw material powders are weighed to obtain the desired composition. The raw material powders may be oxides, carbonates, hydroxides, etc. of the elements contained in the subphase. Ethanol is added to the mixture of the weighed raw material powders, and the mixture is wet-mixed using a ball mill, preferably for 15 hours or more, to obtain a slurry. The obtained slurry is dried, and the mixed powder obtained after drying is calcined, for example, in an air atmosphere at a temperature condition of 600 to 1000°C for 1 to 10 hours to obtain a powdered calcined product of the subphase.

[0046] Next, a dispersant, a binder, and ethanol are added to the obtained calcined main phase and calcined subphase products, and the mixture is pulverized and mixed to obtain a slurry. The obtained slurry is then dried, and the obtained dried product is appropriately granulated and uniaxially pressed under a pressure condition of, for example, 20 MPa to obtain a disk-shaped pre-formed body. The pre-formed body is then subjected to a CIP treatment (cold isostatic pressing treatment) under a pressure condition of, for example, 150 MPa to obtain a green body.

[0047] The obtained compact is then subjected to a binder removal process by, for example, maintaining it at a temperature of 200 to 400° C. for 2 to 10 hours, and then the compact after the binder removal process is fired at a temperature of, for example, 1000 to 1200° C. for 2 to 5 hours in a reducing atmosphere in which the pressure is controlled to be at least one order of magnitude lower than the equilibrium oxygen partial pressure of Ni / NO, to obtain a piezoelectric layer.

[0048] Electrodes made of Au are formed on both the front and back surfaces of the obtained piezoelectric layer, for example, by sputtering. Then, the laminate with the electrodes formed on the piezoelectric layer is subjected to a polarization process in which a DC voltage of 5 kV / mm is applied in silicone oil at 50° C., thereby expressing the voltage characteristics of the piezoelectric layer. In this manner, the piezoelectric element 200 is obtained.

[0049] In the lead-free piezoelectric composition used in the voltage element 200, the subphase is formed of a second crystal phase containing Mn-Ti-O-based oxides, as described above. The size of the crystal grains in this subphase (maximum grain size, D80, average grain size, etc.) can be controlled to a desired size by appropriately setting the grain size of the subphase calcined product and the firing temperature of the molded body after the binder removal treatment performed under a reducing atmosphere. For example, the larger the grain size of the subphase calcined product, the larger the crystal grains of the subphase of the finally obtained lead-free piezoelectric composition. In addition, the higher the firing temperature of the molded body after the binder removal treatment performed under a reducing atmosphere, the larger the crystal grains of the subphase of the finally obtained lead-free piezoelectric composition.

[0050] 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 according to the second embodiment. As shown in FIG. 2, the piezoelectric element 10 of this embodiment includes a piezoelectric layer (an example of a piezoelectric ceramic layer) 11, a plurality of internal electrodes 12, 13 in contact with the piezoelectric layer 11, and two external electrodes 14, 15 connected to the internal electrodes 12, 13. The piezoelectric layer 11 is formed of the above-mentioned lead-free piezoelectric composition. The internal electrodes 12, 13 are mainly composed of a base metal (e.g., nickel). The piezoelectric layer 11 and the internal electrodes 12, 13 are alternately laminated. More specifically, the piezoelectric layer 11 and the internal electrodes 12, 13 are laminated in the order of the piezoelectric layer 11, the internal electrode 12, the piezoelectric layer 11, the internal electrode 13, the piezoelectric layer 11, etc., and one piezoelectric layer 11 is sandwiched between the two internal electrodes 12, 13. The two external electrodes 14, 15 are disposed on the outer surface of a laminate of the piezoelectric layer 11 and the internal electrodes 12, 13. The external electrodes 14, 15 are mainly composed of Au, for example. One end of one internal electrode 12 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.

[0051] Here, an example of a method for manufacturing the piezoelectric element 10 according to the second embodiment will be described. First, a plurality of kinds of raw material powders necessary for forming the main phase are prepared, and the raw material powders are weighed to obtain a target composition. The raw material powders may be oxides, carbonates, hydroxides, etc. of the elements contained in the main phase. Ethanol is added to a mixture of the weighed raw material powders, and the mixture is wet-mixed using a ball mill, preferably for 15 hours or more, to obtain a slurry. The obtained slurry is dried, and the mixed powder obtained after drying is calcined, for example, in an air atmosphere at a temperature condition of 600 to 1000° C. for 1 to 10 hours to obtain a powdered calcined product of the main phase.

[0052] In addition, a plurality of kinds of raw material powders necessary for forming the subphase are prepared, and the raw material powders are weighed to obtain the desired composition. The raw material powders may be oxides, carbonates, hydroxides, etc. of the elements contained in the subphase. Ethanol is added to the mixture of the weighed raw material powders, and the mixture is wet-mixed using a ball mill, preferably for 15 hours or more, to obtain a slurry. The obtained slurry is dried, and the mixed powder obtained after drying is calcined, for example, in an air atmosphere at a temperature condition of 600 to 1000°C for 1 to 10 hours to obtain a powdered calcined product of the subphase.

[0053] Next, a dispersant, a binder, and an organic solvent (e.g., toluene) are added to the obtained calcined main phase and subphase products, and the mixture is pulverized and mixed to obtain a slurry. After that, the slurry is processed into a sheet shape using a doctor blade method or the like to produce a ceramic green sheet.

[0054] Next, an electrode layer that will become an internal electrode is formed on one side of the ceramic green sheet by, for example, screen printing using a conductive paste for the internal electrodes. The electrode layer is mainly composed of a base metal, for example, nickel (Ni).

[0055] Then, the ceramic green sheets on which the electrode layers are formed are stacked so that the electrode layers are exposed alternately from both sides, and ceramic green sheets on which no electrode layers are formed are further stacked on both sides of the obtained laminate. The obtained laminate is pressed to obtain a laminate in which the ceramic green sheets and the electrode layers are alternately stacked. The laminate is cut into a desired shape, and then subjected to a binder removal treatment by, for example, maintaining the laminate at a temperature condition of 200 to 400°C for 2 to 10 hours.

[0056] The laminate after the binder removal process is fired, for example, at a temperature of 1000 to 1200° C. for 2 to 5 hours in a reducing atmosphere in which the pressure is controlled to be one order of magnitude or more lower than the equilibrium oxygen partial pressure of Ni / NO.

[0057] After the side surfaces of the fired laminate are appropriately polished, a pair of external electrodes made of Au are formed on the side surfaces of the laminate by, for example, a sputtering method. The pair of external electrodes are formed facing each other with the laminate between them. The laminate with the external electrodes formed thereon is subjected to a polarization process to obtain a piezoelectric element 10.

[0058] In the lead-free piezoelectric composition used in the voltage element 10, the subphase is formed of a second crystal phase containing Mn-Ti-O-based oxides, as described above. The size of the crystal grains in this subphase (maximum grain size, D80, average grain size, etc.) can be controlled to a desired size by appropriately setting the grain size of the subphase calcined product and the firing temperature of the molded body after the binder removal treatment performed under a reducing atmosphere. For example, the larger the grain size of the subphase calcined product, the larger the crystal grains of the subphase of the finally obtained lead-free piezoelectric composition. In addition, the higher the firing temperature of the molded body after the binder removal treatment performed under a reducing atmosphere, the larger the crystal grains of the subphase of the finally obtained lead-free piezoelectric composition.

[0059] The manufacturing methods of the above-mentioned embodiment 1 and embodiment 2 are both examples, and various other steps and processing conditions for manufacturing a piezoelectric element can be adopted. For example, instead of separately producing the calcined products of the main phase and the subphase and then mixing and firing the powders of both, the raw materials may be mixed in a quantity ratio according to the final composition of the lead-free piezoelectric composition, and the mixture may be fired. However, according to the method of separately producing the calcined products of the main phase and the subphase and then mixing them, the composition of the main phase and the subphase can be more strictly controlled, so that the yield of the lead-free piezoelectric composition can be increased. In addition, metals or alloys such as platinum (Pt), silver-palladium (Ag-Pd), and silver (Ag) may be used as the material of the electrodes.

[0060] The lead-free piezoelectric composition and piezoelectric element disclosed in this specification have excellent piezoelectric properties, a high dielectric breakdown voltage, and excellent insulation properties. Such lead-free piezoelectric composition and piezoelectric element can be widely used for vibration detection, pressure detection, oscillation, piezoelectric device, etc. For example, they can be used in sensors (Knox sensors and combustion pressure sensors, etc.) that detect various vibrations, piezoelectric devices such as vibrators, actuators, and filters, high-voltage generators, micro power sources, various driving devices, position control devices, vibration suppression devices, fluid discharge devices (paint discharge, fuel discharge, etc.), etc. EXAMPLES

[0061] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples in any way.

[0062] [Examples 1 to 7] (Preparation of calcined main phase) As raw material powders, K2CO3 powder, Na2CO3 powder, Nb2O5 powder, TiO2 powder, ZrO2 powder, MnCO3 powder, and BaCO3 powder were prepared, and each of these raw material powders was weighed so that the content (mol%) of each element was the value shown in Table 1. An appropriate amount of ethanol was added to the mixture of each weighed raw material powder, and the mixture was wet-mixed using a ball mill for 15 hours to obtain a slurry. The obtained slurry was dried, and the mixed powder obtained after drying was calcined in an air atmosphere at a temperature condition of 600 to 1100 °C for 1 to 10 hours to obtain a calcined main phase product.

[0063] (Preparation of subphase calcined product) As raw material powders, MnCO3 powder and TiO2 powder were prepared, and each of these raw material powders was weighed to obtain the composition (MnTi2O4) shown in Table 2. An appropriate amount of ethanol was added to the mixture of the weighed raw material powders, and the mixture was wet-mixed for 15 hours using a ball mill to obtain a slurry. The obtained slurry was dried, and the mixed powder obtained after drying was calcined in an air atmosphere at a temperature condition of 600 to 1100°C for 1 to 10 hours to obtain a subphase calcined product.

[0064] (Preparation of piezoelectric elements) A dispersant, binder, and ethanol were added to the obtained main phase calcined product and subphase calcined product, and the mixture was ground and mixed to obtain a slurry. The obtained slurry was then dried, and the obtained dried product was appropriately granulated and uniaxially pressed under a pressure condition of 20 MPa to obtain a disk-shaped pre-formed body. The pre-formed body was then subjected to a CIP treatment (cold isostatic pressing treatment) under a pressure condition of 150 MPa to obtain a green body. The mixing ratio of the main phase calcined product and the subphase calcined product was adjusted so that the ratio (volume %) of the main phase to the subphase was 97:3.

[0065] The obtained compact was subjected to a binder removal treatment by holding it for 2 to 10 hours at a temperature condition of 200 to 400° C. Then, the compact after the binder removal treatment was held and fired for 2 to 5 hours at a temperature condition of 1000 to 1200° C. in a reducing atmosphere in which the pressure was controlled to be one order of magnitude or more lower than the equilibrium oxygen partial pressure of Ni / NO, to obtain a piezoelectric layer.

[0066] Electrodes made of Au were formed on both the front and back surfaces of the obtained piezoelectric layer by a sputtering method. After that, the laminate with the electrodes formed on the piezoelectric layer was subjected to a polarization process in which a direct current voltage of 5 kV / mm was applied in silicone oil at 50° C., thereby expressing the voltage characteristics of the piezoelectric layer and obtaining the piezoelectric element of each example.

[0067] In Examples 1 to 7, the particle size of the subphase calcined product and the firing temperature of the molded body after the binder removal treatment carried out in a reducing atmosphere were appropriately adjusted so as to be different from one another.

[0068] Comparative Example 1 The piezoelectric element of Comparative Example 1 was produced in the same manner as in Example 7, except that the particle size of the subphase calcined product was set to be larger than that of Example 7, and the firing temperature of the molded body after the binder removal treatment performed in a reducing atmosphere was set to be higher than that of Example 7.

[0069] Comparative Example 2 A main phase calcined product was prepared similarly to Example 1. A subphase calcined product was produced by the following method. A Li2CO3 powder and a TiO2 powder were prepared as raw material powders, and a subphase calcined product was produced similarly to Example 1, etc., except that each of these raw material powders was weighed to obtain the composition (LiTi2O4) shown in Table 3. A piezoelectric element of Comparative Example 2 was produced similarly to Example 1, etc., using these main phase calcined products and the subphase calcined products.

[0070] Comparative Example 3 A main phase calcined product was prepared similarly to Example 1. A subphase calcined product was produced by the following method. As raw material powders, Li2CO3 powder, Fe2O3 powder, MgO powder, and TiO2 powder were prepared, and the subphase calcined product was produced similarly to Example 1, etc., except that each of these raw material powders was weighed to obtain the composition (LiFeMgTiO4) shown in Table 3. Using these main phase calcined products and subphase calcined products, a piezoelectric element of Comparative Example 3 was produced similarly to Example 1, etc.

[0071] [Piezoelectric constant d 33 〕 For each piezoelectric element (piezoelectric layer) of Example 3, Comparative Example 2, and Comparative Example 3, d 33 The piezoelectric constant (pC / N) was measured using a piezoelectric meter (product name "ZJ-4B", manufactured by the Institute of Vocal Music, Chinese Academy of Sciences). The results are shown in Table 3.

[0072] [Breakdown voltage] The dielectric breakdown voltage (kV / mm) of each voltage element of each example and each comparative example was measured by the method shown below. With the voltage element placed in silicone oil at 25°C, a DC voltage was applied for 1 minute under the condition of 1 kV / mm, and then the DC voltage was applied for 1 minute each under the condition of the applied voltage being increased by 1 kV / mm. The applied voltage (kV / mm) when the voltage element was broken down was taken as the dielectric breakdown voltage (dielectric breakdown electric field) of the voltage element. The results are shown in Tables 2 and 3.

[0073] [Analysis of main phase] For each voltage element (piezoelectric layer) of each example and each comparative example, using an electron probe microanalyzer (EPMA), the composition analysis of the main phase was performed by the method shown below. The piezoelectric layer of the piezoelectric element was cut in the thickness direction, and the cut surface was polished. Then, the polished surface was photographed at a magnification of 5000 times using EPMA, and from the obtained image, three arbitrary crystal particles in the main phase were selected, and quantitative analysis was performed on these three crystal particles. Then, the average value of the content of each element in these three crystal particles was taken as the content (mol%) of each element in the main phase. The results are shown in Table 1.

[0074] 〔Analysis of secondary phase〕 For each voltage element (piezoelectric layer) of each example and each comparative example, using EPMA, the qualitative analysis of the secondary phase was performed by the method shown below. For each example, the polished surface of the piezoelectric layer used in the analysis of the main phase was photographed at a magnification of 5000 times, and using the obtained image, elemental mapping of Mn (manganese) and Ti (titanium) was performed. Then, from the obtained elemental mapping image, it was confirmed that Mn and Ti are present in the secondary phase. For Comparative Example 2, elemental mapping of Li (lithium), Fe (iron), Mg (magnesium) and Ti (titanium) was performed, and from the obtained elemental mapping image, it was confirmed that Li, Fe, Mg and Ti are present in the secondary phase. For Comparative Example 3, elemental mapping of Mn (manganese) and Ti (titanium) was performed, and from the obtained elemental mapping image, it was confirmed that Mn and Ti are present in the secondary phase.

[0075] Also, for the polished surfaces of each example and each comparative example, using the powder X-ray diffraction method (XRD: X-ray diffraction), the composition of the compound contained in the secondary phase was identified. The measurement conditions of XRD are as follows.

[0076] <Measurement conditions of XRD> Measuring device: Powder X-ray diffractometer Range: 50.00° to 70.00° Wavelength: 0.7 angstroms

[0077] [Subphase crystal grain size (maximum grain size, average grain size, D80)] The polished surface of each example and each comparative example was photographed at a magnification of 1000 times or 10000 times using a scanning electron microscope (SEM), and a square measurement range with a side of 250 μm was set for the obtained SEM image (reflected electron image). Then, for a plurality of crystal grains present within the measurement range, the long axis diameter and the short axis diameter were obtained using image analysis software. The long axis diameter and the short axis diameter of the crystal grain were mutually perpendicular, and the long axis diameter and the short axis diameter were each the maximum value on each axis. Then, for each crystal grain, the average value of the long axis diameter and the short axis diameter was taken as the grain size (particle size) of each crystal grain. The average value of the grain size of each crystal grain within the measurement range thus obtained was taken as the average grain size (μm) of the subphase crystal grains.

[0078] The magnification for taking the SEM images was first 1000x. Then, when each crystal particle could not be identified from the obtained SEM images, the magnification was changed to 10000x. As a result, only Example 1 had its SEM images taken at a magnification of 10000x, and the other cases had their SEM images taken at a magnification of 1000x.

[0079] The largest major axis diameter of each crystal grain within the above measurement range was taken as the maximum grain size (μm) of the subphase crystal grains. The results are shown in Tables 2 and 3.

[0080] In addition, for each crystal particle within the above measurement range, a particle size distribution was created in order of particle size from smallest to largest, and the cumulative 80% particle size (D80) based on the number of particles was calculated for the particle size distribution. The results are shown in Tables 2 and 3.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] As shown in Table 2, the lead-free piezoelectric compositions used in the piezoelectric elements of Examples 1 to 7 have a subphase made of MnTi2O4 (Mn-Ti-O oxide). In Examples 1 to 7, the maximum grain size of the crystal grains in the subphase is 35 μm or less, and the cumulative 80% grain size (D80) based on the number is 32 μm or less. It was confirmed that Examples 1 to 7 have a dielectric breakdown voltage of 16 kV / mm or more, and have excellent insulating properties.

[0085] Furthermore, as shown in Table 3, the results of the measurement of the piezoelectric constant of Example 3, which was performed as a representative of the examples, confirmed that the lead-free piezoelectric composition used in the piezoelectric elements of Example 3 and the like has excellent piezoelectric properties.

[0086] Comparative Example 1 has a subphase made of MnTi2O4 (Mn-Ti-O oxide), but the maximum grain size (29 μm) and the cumulative 80% grain size (D80) (37 μm) of the crystal grains in the subphase are both too large. In such Comparative Example 1, the dielectric breakdown voltage was 13 kV / mm, and it was confirmed that the insulating properties were low.

[0087] Comparative Example 2 is a case in which a compound (LiTi2O4) containing Ti (titanium) but not Mn (manganese) is provided as a subphase. Although Comparative Example 2 has excellent piezoelectric properties like Example 3, it was confirmed that the dielectric breakdown voltage was 10 kV / mm and the insulating properties were low.

[0088] Comparative Example 3 is a case in which a compound (LiFeMgTiO4) containing Ti (titanium) but not Mn (manganese) is provided as a subphase. Although Comparative Example 3 has excellent piezoelectric properties like Example 3, it was confirmed that the dielectric breakdown voltage was 12 kV / mm and the insulating properties were low.

[0089] [Examples 8 to 10] The main phase calcined product was prepared in the same manner as in Example 1. The subphase calcined product was produced by the following method. As raw material powders, MnCO3 powder and TiO2 powder were prepared, and each of these raw material powders was weighed to have the composition (Mn2TiO4) shown in Table 2. An appropriate amount of ethanol was added to the mixture of each weighed raw material powder, and the mixture was wet-mixed using a ball mill for 15 hours to obtain a slurry. The obtained slurry was dried, and the mixed powder obtained after drying was calcined in an air atmosphere at a temperature condition of 600 to 1100 ° C for 1 to 10 hours to obtain a subphase calcined product. Using these main phase calcined products and subphase calcined products, the piezoelectric elements of Examples 8 to 10 were produced in the same manner as in Example 1, etc.

[0090] For each of the piezoelectric elements of Examples 8 to 10, the main phase was analyzed, the subphase was analyzed, the dielectric breakdown voltage (kV / mm) was measured, and the grain size (maximum grain size, average grain size, D80) of the subphase crystal grains was measured by the same methods as in Example 1, etc. The results are shown in Table 4.

[0091] [Table 4]

[0092] As shown in Table 4, the lead-free piezoelectric compositions used in the piezoelectric elements of Examples 8 to 10 have a subphase made of Mn2TiO4 (Mn-Ti-O oxide). In Examples 8 to 10, the maximum grain size of the crystal grains in the subphase is 35 μm or less, and the cumulative 80% grain size (D80) based on the number is 32 μm or less. It was confirmed that Examples 8 to 10 have a dielectric breakdown voltage of 16 kV / mm or more, and have excellent insulating properties. [Explanation of symbols]

[0093] 10,200...piezoelectric element, 11,100...piezoelectric layer (piezoelectric ceramic layer), 12,13...internal electrodes, 14,15...external electrodes, 301,302...electrodes

Claims

1. a main phase including an alkali niobate perovskite oxide; and a subphase containing an Mn—Ti—O-based oxide, The lead-free piezoelectric composition has a maximum particle size of the Mn-Ti-O oxide in the subphase of 35 μm or less, and a number-based cumulative 80% particle size (D80) of 32 μm or less.

2. 2. The lead-free piezoelectric composition according to claim 1, wherein the average particle size of the Mn--Ti--O based oxide in the subphase is 24 μm or less.

3. The Mn-Ti-O oxide is MnTi ２ O ４ or Mn ２ TiO ４ The lead-free piezoelectric composition according to claim 1 or claim 2, comprising:

4. A piezoelectric element comprising a laminate of a piezoelectric ceramic layer formed of the lead-free piezoelectric composition according to claim 1 or 2 and an electrode attached to the piezoelectric ceramic layer.

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