Piezoelectric element and method for manufacturing piezoelectric element

Abstract

To provide a piezoelectric element capable of improving insulation quality by reducing dielectric loss.SOLUTION: A piezoelectric element comprises: a piezoelectric body, consisting of a lead-free piezoelectric magnetic composition satisfying b / (d3+d4+d5)≤1, including a main phase consisting of a niobate alkali-based perovskite type oxide expressed by a composition formula (A1aM1b)c(Nbd1Mnd2Tid3Zrd4Hfd5)O3+e ( wherein an element A1 is at least one of alkali metals, an element M1 is at least one of Ba, Ca and Sr, it leads 0<a<1, 0<b<1 and a+b=1, c satisfies 0.80<c<1.10, it leads 0<d1<1, 0<d2<1, 0<d3<1, 0≤d4<1, 0≤d5<1 and d1+d2+d3+d4+d5=1 and e is a value indicating deficient or excessive oxygen; and an electrode containing a base metal as a main component and being in contact with the piezoelectric body.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a piezoelectric element and a method for manufacturing a piezoelectric element. [Background technology]

[0002] Traditionally, PZT (lead zirconate titanate) has been widely used as a ceramic that exhibits piezoelectricity. However, because PZT contains lead, its environmental impact has been a concern, and there is a demand for the development of lead-free piezoelectric ceramics.

[0003] Piezoelectric ceramic electronic components are typically manufactured by laminating ceramic green sheets, which serve as piezoelectric ceramic layers, with conductive films, which serve as electrodes, and then co-firing them. Pt, Ag-Pd alloys, and other materials are commonly used as electrode materials. However, these electrode materials are expensive and prone to migration. In recent years, nickel (Ni), which is inexpensive and can suppress migration, has been proposed as an alternative. Ni is easily oxidized when fired in an air atmosphere, so it must be fired in a reducing atmosphere. However, when lead-containing zirconate titanate or lead titanate-based materials are used as piezoelectric ceramic materials, firing these materials in a reducing atmosphere reduces the lead, making it impossible to obtain the desired stable piezoelectric properties.

[0004] In recent years, various lead-free piezoelectric ceramic compositions with alkali niobate perovskite oxide as the main phase have been developed as promising candidates for lead-free piezoelectric ceramic materials that do not contain lead and exhibit piezoelectricity even when fired in a reducing atmosphere (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 5862983 [Patent Document 2] Japanese Patent No. 6489333

Summary of the Invention

Problems to be Solved by the Invention

[0006] The lead-free piezoelectric ceramic composition as described above has a relatively large dielectric loss (tanδ) of about 5%, and there are concerns about insulation and the like. Therefore, when polarization treatment is performed at several tens of degrees Celsius with a high electric field applied, or when driven as a device, there is a risk of leakage or dielectric breakdown, and the temperature is likely to rise.

Means for Solving the Problems

[0007] The piezoelectric element disclosed by this specification has a composition formula (A1 a M1 b ) c (Nb d1 Mn d2 Ti d3 Zr d4 Hf d5 )O 3+e (where the element A1 is at least one of alkali metals, the element M1 is at least one of Ba, Ca, Sr, 0 < a < 1, 0 < b < 1, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, 0 < d2 < 1, 0 < d3 < 1, 0 ≤ d4 < 1, 0 ≤ d5 < 1, d1 + d2 + d3 + d4 + d5 = 1, and e represents a value of oxygen deficiency or excess). It includes a main phase composed of an alkali niobate perovskite-type oxide represented by a lead-free piezoelectric magnetic composition that satisfies b / (d3 + d4 + d5) ≤ 1, a piezoelectric body, and a base metal-based electrode in contact with the piezoelectric body.

[0008] Also, the manufacturing method of the piezoelectric element disclosed by this specification has a composition formula (A1 a M1 b ) c (Nb d1 Mn d2 Ti d3 Zr d4 Hf d5 )O 3+e(However, element A1 is at least one of alkali metals, element M1 is at least one of Ba, Ca, and Sr, 0 < a < 1, 0 < b < 1, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, 0 < d2 < 1, 0 < d3 < 1, 0 ≤ d4 < 1, 0 ≤ d5 < 1, d1 + d2 + d3 + d4 + d5 = 1, and e represents a value indicating oxygen deficiency or excess), including a main phase composed of an alkali niobate perovskite-type oxide, mixing raw materials of a lead-free piezoelectric composition satisfying b / (d3 + d4 + d5) ≤ 1, firing to obtain a calcined powder, a molding step of creating a molded body containing the calcined powder, an electrode forming step of forming an electrode layer mainly composed of a base metal on the molded body, and a co-firing step of co-firing the molded body and the electrode layer in a reducing atmosphere.) [Advantages of the Invention]

[0009] According to the piezoelectric element and the method for manufacturing a piezoelectric element disclosed herein, dielectric loss can be reduced and insulation can be improved. [Brief Description of the Drawings]

[0010] [Figure 1] Cross-sectional view of the piezoelectric element of the embodiment [Embodiments of the Invention]

[0011] [Overview of the Embodiment] (1) The piezoelectric element disclosed herein has a composition formula (A1 a M1 b ) c (Nb d1 Mn d2 Ti d3 Zr d4 Hf d5 )O 3+e(However, element A1 is at least one of alkali metals, element M1 is at least one of Ba, Ca, and Sr, 0 < a < 1, 0 < b < 1, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, 0 < d2 < 1, 0 < d3 < 1, 0 ≤ d4 < 1, 0 ≤ d5 < 1, d1 + d2 + d3 + d4 + d5 = 1, and e represents a value indicating oxygen deficiency or excess), and includes a main phase composed of an alkali niobate perovskite-type oxide, and a piezoelectric body composed of a lead-free piezoelectric composition satisfying b / (d3 + d4 + d5) ≤ 1, a base metal as a main component, and an electrode in contact with the piezoelectric body.

[0012] In addition, the method for manufacturing a piezoelectric element disclosed by this specification has a composition formula (A1 a M1 b ) c (Nb d1 Mn d2 Ti d3 Zr d4 Hf d5 )O 3+e (However, element A1 is at least one of alkali metals, element M1 is at least one of Ba, Ca, and Sr, 0 < a < 1, 0 < b < 1, a + b = 1, c satisfies 0.80 < c < 1.10, 0 < d1 < 1, 0 < d2 < 1, 0 < d3 < 1, 0 ≤ d4 < 1, 0 ≤ d5 < 1, d1 + d2 + d3 + d4 + d5 = 1, and e represents a value indicating oxygen deficiency or excess), and includes a main phase composed of an alkali niobate perovskite-type oxide, and includes a pre-firing step of mixing raw materials of a lead-free piezoelectric composition satisfying b / (d3 + d4 + d5) ≤ 1 and firing to obtain pre-fired powder, a molding step of creating a molded body containing the pre-fired powder, an electrode forming step of forming an electrode layer mainly composed of a base metal on the molded body, and a co-firing step of co-firing the molded body and the electrode layer in a reducing atmosphere.

[0013] According to the above configuration, by appropriately containing Ti, Zr, and Hf in the B site (niobium site) of the alkali niobate perovskite-type oxide, the sinterability of the piezoelectric body is improved, the dielectric loss is reduced, and the insulation property is improved.

[0014] Furthermore, when Mn dissolves in the B site as an acceptor, it can compensate for the charge caused by oxygen vacancies formed during reduction firing, reducing dielectric loss and improving insulation properties. However, Mn does not dissolve easily in alkali niobate perovskite oxides and is prone to segregation as a heterophase in lead-free piezoelectric ceramic compositions. On the other hand, when Ba, Ca, and Sr dissolve in the A site (alkali site), piezoelectric performance improves. However, because Ba, Ca, and Sr act as donors, there is concern that the insulating properties may deteriorate when the piezoelectric material becomes a semiconductor.

[0015] By adjusting the composition ratio of Ti, Zr, Hf to Ba, Ca, and Sr so that b / (d3+d4+d5)≦1, it is possible to suppress the formation of a semiconductor due to the solid solution of Ba, Ca, and Sr in the A site while forming an appropriate amount of solid solution of Ti, Zr, Hf, and Mn, thereby reducing dielectric loss and improving insulation properties.

[0016] 2) In the piezoelectric element of 1) above, the molar ratio of Mn atoms to Nb atoms (Mn / Nb) contained in the main phase may be 0.003 or more.

[0017] In the method for producing a piezoelectric element according to 1) above, in the calcination step, the molar ratio of Mn atoms to Nb atoms (Mn / Nb) contained in the raw material mixture may be 0.005 or more.

[0018] By adjusting the molar ratio of Mn atoms to Nb atoms as described above, it is possible to reliably reduce the dielectric loss of the piezoelectric body and improve the insulating properties.

[0019] 3) In the piezoelectric element of 1) above, the average particle size of the crystal grains of the alkali niobate perovskite oxide contained in the main phase may be less than 6 μm.

[0020] If the average grain size of the crystal grains is less than 6 μm, the grain boundary resistance is large, so that the deterioration of the piezoelectric properties can be avoided.

[0021] 4) In the piezoelectric element of 1), the lead-free piezoelectric magnetic composition further comprises a compound represented by the composition formula A2 1-x Ti 1-x Nb 1+x The subphase may include a compound represented by the composition formula A3Ti3NbO9 (wherein the element A2 is at least one alkali metal and satisfies 0≦x≦0.15) and a compound represented by the composition formula A3Ti3NbO9 (wherein the element A3 is at least one alkali metal).

[0022] With this configuration, the lead-free piezoelectric ceramic composition can have improved piezoelectric properties compared to a case where the lead-free piezoelectric ceramic composition does not have a subphase.

[0023] 5) The piezoelectric element of 1) above may have a configuration in which the piezoelectric body and the electrodes are alternately laminated.

[0024] [Details of the embodiment] Specific examples of the technology disclosed in this specification will be described below with reference to the drawings. Note that the present invention is not limited to these examples, but is defined by the claims, and is intended to include all modifications within the meaning and scope of the claims.

[0025] <Embodiment> [Piezoelectric element 10] The piezoelectric element 10 of this embodiment includes a piezoelectric layer 11 (an example of a piezoelectric body), multiple internal electrodes 12 and 13 (an example of electrodes) 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 made of a lead-free piezoelectric ceramic composition containing a main phase of an alkali niobate perovskite oxide. The internal electrodes 12 and 13 are primarily composed of a base metal, for example, Ni (nickel). 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..., 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. Of the two internal electrodes 12, 13 in contact with one piezoelectric layer 11, one end of one internal electrode 12 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.

[0026] [Configuration of lead-free piezoelectric magnetic composition] The lead-free piezoelectric magnetic composition constituting the piezoelectric layer 11 includes a main phase made of an alkali niobate perovskite oxide having piezoelectric properties. The alkali niobate perovskite oxide of this embodiment is represented by the following composition formula (1).

[0027] (A1 a M1 b ) c (Nb d1 Mn d2 Ti d3 Zr d4 Hf d5 )O 3+e …(1)

[0028] The element A1 is at least one alkali metal, and the element M1 is at least one alkaline earth metal selected from the group consisting of calcium (Ca), strontium (Sr), and barium (Ba).

[0029] In the above compositional formula (1), element A1 and element M1 are arranged at the A-site (alkali-site) of the perovskite structure, and Nb (niobium), Mn (manganese), Ti (titanium), Zr (zirconium), and Hf (hafnium) are arranged at the B-site.

[0030] As the values of coefficients a to e in the above compositional formula (1), among the combinations of values that form a perovskite structure, preferred values are selected from the perspective of the electrical properties or piezoelectric properties (especially the piezoelectric constant d 33 ) of the lead-free piezoelectric ceramic composition.

[0031] Specifically, 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 metals) and b = 0 (i.e., a composition containing neither Ca, Sr, nor Ba) are excluded.

[0032] Coefficient c with respect to the entire A-site satisfies 0.80 < c < 1.10, preferably 0.84 ≤ c ≤ 1.08, and more preferably 0.88 ≤ c ≤ 1.07.

[0033] Coefficients d1, d2, d3, d4, d5 satisfy 0 < d1 < 1, 0 < d2 < 1, 0 < d3 < 1, 0 ≤ d4 < 1, 0 ≤ d5 < 1, and d1 + d2 + d3 + d4 + d5 = 1. d1 = 0 (a composition not containing Nb), d2 = 0 (a composition not containing Mn), and d3 = 0 (a composition not containing Ti) are excluded. The coefficient d4 of Zr and the coefficient d5 of Hf may be zero (i.e., the composition does not contain one or both of Zr or Hf).

[0034] Among the coefficients 3 + e of oxygen, 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 of oxygen (3 + e) can take a value that constitutes a perovskite-type oxide as the main phase. A typical value of coefficient e is e = 0, and preferably 0 ≤ e ≤ 0.1. The value of 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.

[0035] The coefficients b, d3, d4, and d5 satisfy the relationship b / (d3+d4+d5)≦1. If the coefficients b, d3, d4, and d5 are within this range, a lead-free piezoelectric ceramic composition with low dielectric loss and high insulating properties can be obtained. The reason for this is presumed to be as follows.

[0036] By incorporating appropriate amounts of Ti, Zr, and Hf into the B site (niobium site) of an alkali niobate perovskite oxide, the sinterability of the piezoelectric body is improved, the dielectric loss is reduced, and the insulating properties are improved.

[0037] Furthermore, when Mn dissolves in the B site as an acceptor, it can compensate for the charge caused by oxygen vacancies formed during reduction firing, reducing dielectric loss and improving insulation properties. However, Mn does not dissolve easily in alkali niobate perovskite oxides and is prone to segregation as a heterophase in lead-free piezoelectric ceramic compositions. On the other hand, when Ba, Ca, and Sr dissolve in the A site (alkali site), piezoelectric performance improves. However, because Ba, Ca, and Sr act as donors, there is concern that the insulating properties may deteriorate when the piezoelectric material becomes a semiconductor.

[0038] By adjusting the composition ratio of Ti, Zr, Hf to Ba, Ca, and Sr so that b / (d3+d4+d5)≦1, it is possible to suppress the formation of a semiconductor due to the solid solution of Ba, Ca, and Sr in the A site while forming an appropriate amount of solid solution of Ti, Zr, Hf, and Mn, thereby reducing dielectric loss and improving insulation properties.

[0039] The alkali niobate perovskite oxide represented by the above composition formula (1) preferably contains at least one of K (potassium), Na (sodium), and Li (lithium) as the element A1. When the above oxide contains at least one of K, Na, and Li as the element A1 and at least one of Ca, Sr, and Ba as the element M1, composition formula (1) can be rewritten as the following composition formula (1a).

[0040] (Ka1 Na a2 Li a3 Ca b1 Sr b2 Ba b3 ) c (Nb d1 Mn d2 Ti d3 Zr d4 Hf d5 )O 3+e …(1a)

[0041] The above compositional formulas (1) and (1a) are equivalent, a1 + a2 + a3 = a, and b1 + b2 + b3 = b. The coefficients a1 and a2 of K and Na are typically 0 < a1 ≤ 0.6, 0 < a2 ≤ 0.6. The coefficient a3 of Li may be zero, but 0 < a3 ≤ 0.2 is preferred, and 0 < a3 ≤ 0.1 is more preferred.

[0042] Among the alkali niobate perovskite-type oxides represented by the above compositional formula (1a), the oxides having K, Na, and Nb as main metal components are referred to as "KNN" or "KNN material". By using this oxide, a lead-free piezoelectric magnetic composition excellent in piezoelectric properties, electrical properties, insulation properties, and high-temperature durability, and having no abrupt change in properties between -50°C and +150°C can be obtained. A typical composition of the main phase is (K,Na,Li,Ca,Ba) c (Nb,Mn,Ti,Zr,Hf)O 3+e is.

[0043] The lead-free piezoelectric ceramic composition of this embodiment may contain a sub-phase composed of one of the oxides represented by the following compositional formula (2) or the oxides represented by the following compositional formula (3).

[0044] A2 1-x Ti 1-x Nb 1+x O5…(2) A3Ti3NbO9…(3)

[0045] In composition formula (2), element A2 is at least one alkali metal, and preferably at least one of K, Rb (rubidium), and Cs (cesium). The coefficient x satisfies 0≦x≦0.15. If the coefficient x is a value within this range, the structure of the subphase is stabilized, and a uniform crystalline phase can be obtained. From the viewpoint of structural stability of the subphase, the coefficient x preferably satisfies 0≦x≦0.15 when element A2 is K or Rb, and preferably satisfies 0≦x≦0.10 when element A2 is Cs.

[0046] In composition formula (3), element A3 is at least one alkali metal, and is preferably at least one of K, Rb, and Cs.

[0047] Although the subphase does not have piezoelectric properties, its presence in the main phase improves sinterability and also improves insulation. It is also believed to contribute to preventing a phase transition point from occurring between -50°C and +150°C. The subphase is a layer structure compound (or layer compound), and it is believed that the fact that it is a layer structure compound contributes to improving the insulation properties of the piezoelectric ceramic composition and preventing a phase transition point from occurring.

[0048] The content of the subphase may be more than 0 mol % and less than 20 mol %, but is preferably 2 mol % to 15 mol %, and more preferably 2 mol % to 10 mol %.

[0049] Among the oxides represented by composition formula (2) or (3), oxides containing Nb, Ti, and K as the main metal components are called "NTK materials." By using these oxides, lead-free piezoelectric magnetic compositions with excellent piezoelectric properties can be obtained at low cost.

[0050] The molar ratio of Mn atoms to Nb atoms contained in the main phase (Mn / Nb) is preferably 0.003 or more. By adjusting in this manner, the dielectric loss of the piezoelectric layer 11 can be reliably reduced and the insulating properties can be improved.

[0051] The average particle size of the crystal grains of the alkali niobate perovskite oxide contained in the main phase is preferably less than 6 μm, which results in high grain boundary resistance and can prevent degradation of the piezoelectric properties.

[0052] [Method of manufacturing the piezoelectric element 10] An example of a method for manufacturing the piezoelectric element 10 will be described below.

[0053] 1. Pre-firing process First, necessary raw material powders for the main phase are selected and weighed to achieve the desired composition. The raw material powders may be oxides, carbonates, or hydroxides of the elements contained in the main phase. The molar ratio of Mn atoms to Nb atoms (Mn / Nb) contained in the mixture of raw material powders for the main phase is adjusted to 0.005 or greater. Ethanol is added to these raw material powders, and the mixture is wet-mixed in a ball mill, preferably for 15 hours or more, to obtain a slurry. The resulting slurry is dried, and the resulting mixed powder is calcined, for example, in air at 600 to 1000°C for 1 to 10 hours, to obtain a calcined main phase product (calcination step).

[0054] Although there is no particular upper limit to the molar ratio (Mn / Nb) of Mn atoms to Nb atoms contained in the mixture of raw material powders for the main phase, it is preferable that Mn / Nb≦0.1 If the molar ratio (Mn / Nb) is greater than 0.1, sintering may become difficult.

[0055] Furthermore, necessary raw material powders for the subphase are selected and weighed to achieve the desired composition. The raw material powders may be oxides, carbonates, or hydroxides of the elements contained in the subphase. Ethanol is then added to these raw material powders and wet-mixed in a ball mill, preferably for 15 hours or more, to obtain a slurry. The resulting slurry is dried, and the resulting mixed powder is calcined, for example, in an air atmosphere at 600 to 1000°C for 1 to 10 hours to obtain a calcined subphase.

[0056] Next, the main phase calcined product and the subphase calcined product are weighed separately, and a dispersant, a binder, and an organic solvent such as toluene are added thereto, followed by pulverization and mixing to form a slurry. Thereafter, the slurry is processed into a sheet shape using a doctor blade method or the like to produce a ceramic green sheet (an example of a green body) (forming step).

[0057] Next, an electrode layer that will become an internal electrode is formed on one surface of the ceramic green sheet by, for example, screen printing using a conductive paste for the internal electrode (electrode formation step). The electrode layer is mainly composed of a base metal, for example, Ni.

[0058] Next, a plurality of ceramic green sheets with electrode layers formed thereon are stacked, and then ceramic green sheets without electrode layers are stacked on both sides of the stacked green sheets, and the stacked green sheets and electrode layers are pressed together to obtain a laminate in which the ceramic green sheets and electrode layers are alternately stacked. After cutting the laminate into a desired shape, the laminate is subjected to a binder removal treatment, for example, by holding the laminate at 200 to 400°C for 2 to 10 hours.

[0059] The laminate after the binder removal treatment is fired, for example, at 900 to 1200° C. for 2 to 5 hours in a reducing atmosphere with an oxygen partial pressure adjusted to prevent oxidation of the electrode layer (co-firing step).

[0060] After firing, external electrodes made of Au are formed on the outer surfaces of the laminate by, for example, sputtering, and a polarization process is performed to obtain a piezoelectric element.

[0061] The above-described manufacturing method is merely an example, and various other steps and processing conditions for manufacturing piezoelectric elements can be used. For example, instead of separately producing calcined products of the main phase and subphase and then mixing and firing the powders of both, the raw materials may be mixed in a quantitative ratio corresponding to the final composition of the lead-free piezoelectric ceramic composition and then fired. However, if the calcined products of the main phase and subphase are separately produced and then mixed, the compositions of the main phase and subphase can be more strictly controlled, making it possible to increase the yield of the lead-free piezoelectric ceramic composition.

[0062] The lead-free piezoelectric ceramic composition and piezoelectric element of this embodiment can be widely used in vibration detection applications, pressure detection applications, oscillation applications, piezoelectric device applications, etc. For example, they can be used in sensors that detect various vibrations (knock sensors, combustion pressure sensors, etc.), piezoelectric devices such as vibrators, actuators, and filters, high-voltage generators, micropower sources, various drive devices, position control devices, vibration suppression devices, and fluid discharge devices (paint discharge, fuel discharge, etc.). Furthermore, the lead-free piezoelectric ceramic composition and piezoelectric element of this embodiment are particularly suitable for applications requiring excellent thermal durability (for example, knock sensors, combustion pressure sensors, etc.).

[0063] In this embodiment, an example is shown in which the piezoelectric element 10 has a configuration in which the piezoelectric layers 11 and the internal electrodes 12 and 13 are alternately stacked, but the piezoelectric element may also have a single-layer structure comprising a layer of piezoelectric material and an electrode disposed on the surface of the piezoelectric material.

[0064] <Test example> 1. Test Example 1 (1) Preparation of samples K2CO3 powder, Na2CO3 powder, and Nb2O5 powder were weighed and mixed so that the coefficients f and g of the following composition formula (2) were in the ratios shown in Table 1.

[0065] (K f Na g )NbO3…(2)

[0066] Additionally, the necessary powders were selected from BaCO3 powder, CaCO3 powder, and SrCO3 powder, and were weighed and added so that the total molar percentage of Ba atoms, Ca atoms, and Sr atoms relative to the Nb atoms contained in the Nb2O5 powder would be the value shown in Table 1. Additionally, MnO2 powder, TiO2 powder, ZrO2 powder, and HfO2 powder were weighed and added so that the molar percentage of the metal atoms in each powder relative to the Nb atoms contained in the Nb2O5 powder would be the value shown in Table 1.

[0067] Ethanol was added to the mixture of these raw material powders and wet-mixed in a ball mill for 15 hours or more to obtain a slurry. The resulting slurry was dried and the resulting mixed powder was calcined in air at 600-1000°C for 1-10 hours to obtain a calcined powder.

[0068] The calcined powder was then crushed and mixed with a dispersant, binder, and an organic solvent such as toluene to form a slurry. This was then processed into a sheet using the doctor blade method to produce a ceramic green sheet. Several of the resulting ceramic green sheets were stacked and pressed together, and then cut into disks to obtain compacts.

[0069] The conductive paste for electrodes was applied to both sides of the obtained molded body by screen printing to form electrode layers (electrode formation step). As shown in Table 2, the content ratio of the electrode components contained in the conductive paste for electrodes was 100% Ni for Sample No. 1-24, and 90% Cu and 10% Ni by mass for Sample No. 25.

[0070] The compact with the electrode layer formed was held at 200-400°C for 2-10 hours to remove the binder, and then co-fired at 900-1200°C for 2-5 hours in a reducing atmosphere with an oxygen partial pressure controlled so that the electrode layer does not oxidize. The resulting fired compact was subjected to polarization treatment by applying an electric field of 5 kV / mm in silicone oil at 50°C to prepare a sample. The resulting sample was a piezoelectric element comprising a piezoelectric body made of a lead-free piezoelectric magnetic composition consisting of an alkali niobate perovskite oxide represented by the above composition formula (1a), and an electrode layer formed on the surface of the piezoelectric body.

[0071] [Table 1]

[0072] (2) Test method The obtained samples were measured using an impedance analyzer (Keysight Technologies, E4990A), and the dielectric loss tangent delta (tanδ) was calculated from the capacitance value at room temperature and 1 kHz. The electromechanical coupling coefficient kp was also determined using the resonance-antiresonance method. Samples with a dielectric loss tangent delta of 3.0% or less and an electromechanical coupling coefficient kp of 20% or more were deemed to be non-defective.

[0073] The obtained samples were also subjected to a dielectric breakdown test. Specifically, an electric field of 5 kV / mm was applied for 30 minutes or more in silicone oil at 50°C to check whether dielectric breakdown occurred. If dielectric breakdown occurred, the sample was evaluated as "x", and if no dielectric breakdown occurred, the sample was evaluated as "o".

[0074] (3) Results For each sample, the sum of the molar percentages of Ca atoms, Sr atoms, and Ba atoms relative to Nb atoms in the mixture of raw material powders weighed in 1.(1) above was defined as P M1 The mole percentages of Ti atoms, Zr atoms, and Hf atoms relative to Nb atoms are P Ti , P Zr , P Hf and P M1 / (P Ti +P Zr +P Hf ) was determined. Elemental analysis was also performed on three points on the main phase particles using an electron probe microanalyzer (EPMA) with a beam diameter of φ1 μm for each sample to measure the molar ratio of Mn atoms to Nb atoms. The average value of the three points was calculated as the molar ratio of Mn atoms to Nb atoms in the main phase (Mn / Nb). These values ​​are shown in Table 2, along with the dielectric loss tangent delta, electromechanical coupling coefficient kp, and the results of the dielectric breakdown test.

[0075] [Table 2]

[0076] Theoretically, all of the Ca, Sr, and Ba atoms in the raw material powder will occupy the A site of the resulting alkali niobate perovskite oxide. Also, all of the Ti, Zr, and Hf atoms will occupy the B site of the resulting alkali niobate perovskite oxide. Therefore, the total mole percentage of Ba, Ca, and Sr atoms, P M1 It can be considered that the molar percentages of Ti atoms, Zr atoms, and Hf atoms correspond to the coefficients d3, d4, and d5 of Ti, Zr, and Hf, respectively, in the composition formula (1a). M1 / (P Ti +P Zr +P Hf ) can be considered to be equivalent to the relational expression b / (d3+d4+d5) between the coefficients b, d2, and d3 in the composition formula (1).

[0077] P M1 / (P Ti +P Zr +P Hf Samples No. 1 and 2, in which the value of b / (d3 + d4 + d5) was 1 or greater, had a dielectric loss of 3.0% or greater and underwent dielectric breakdown in the dielectric breakdown test. Sample No. 3, which did not contain Mn, also had a dielectric loss of 3.0% or greater and underwent dielectric breakdown in the dielectric breakdown test. Sample No. 4, which did not contain Ti, also had a dielectric loss of 3.0% or greater and underwent dielectric breakdown in the dielectric breakdown test. Furthermore, sample No. 10, in which the molar percentage of Mn atoms relative to Nb atoms contained in the raw material mixture was 0.1% (i.e., the molar ratio of Mn atoms to Nb atoms contained in the raw material mixture (Mn / Nb) was 0.001), also had a dielectric loss of 3.0% or greater and underwent dielectric breakdown in the dielectric breakdown test.

[0078] Samples No. 5-9 and No. 11-25 contain element A1 (at least one of alkali metals), element M1 (at least one of Ba, Ca, and Sr), Mn, and Ti as essential components, and do not contain P. M1 / (P Ti +P Zr+P Hf ) (i.e., the value of b / (d3+d4+d5)) is 1 or less, the molar percentage of Mn atoms to Nb atoms contained in the raw material mixture is 0.5% or more (i.e., the molar ratio of Mn atoms to Nb atoms contained in the raw material mixture (Mn / Nb) is 0.005 or more), and the molar ratio of Mn atoms to Nb atoms contained in the main phase (Mn / Nb) is 0.003 or more. These samples had a dielectric loss of 3.0% or less, an electromechanical coupling coefficient of 20% or more, did not undergo dielectric breakdown in dielectric breakdown tests, and were confirmed to have excellent piezoelectric properties.

[0079] 2. Test Example 2 (1) Sample preparation and test method Samples Nos. 26-29 having the same composition as Sample No. 5 were obtained in the same manner as in Test Example 1 (see Table 3). These samples were adjusted so that the particle sizes of the crystal particles of the alkali niobate perovskite oxide were different from each other by varying the firing temperatures in the firing step.

[0080] [Table 3]

[0081] The obtained sample was imaged at 5000x magnification using a SEM (Hitachi High-Tech Corporation, TM4000Plus), and the average particle size of the crystal particles in the image was taken as the average particle size. Furthermore, the obtained sample was subjected to the same procedures as in Test Example 1 above to determine the dielectric loss tan δ and the electromechanical coupling coefficient kp, and a dielectric breakdown test was also conducted.

[0082] (2) Results For each sample, the dielectric loss tan δ, electromechanical coupling coefficient kp, and the results of the dielectric breakdown test are shown in Table 4, along with the average particle size.

[0083] [Table 4]

[0084] Sample No. 29, which contained crystal grains with an average grain size of 6 μm, had a dielectric loss of 3.0% or more and suffered breakdown in the dielectric breakdown test. In contrast, Sample No. 5 and Samples No. 26-28, which contained crystal grains with an average grain size of less than 6 μm, had a dielectric loss of 3.0% or less, an electromechanical coupling coefficient of 20% or more, did not suffer breakdown in the dielectric breakdown test, and were confirmed to have excellent piezoelectric properties. [Explanation of symbols]

[0085] 10: Piezoelectric element 11: Piezoelectric layer (piezoelectric body) 12, 13: Internal electrode (electrode)

Claims

1. Composition formula (A1 ａ M1 ｂ ) ｃ (Nb ｄ１ Mn ｄ２ Ti ｄ３ Zr ｄ４ Hf ｄ５ ) O ３＋ｅ (wherein element A1 is at least one alkali metal, element M1 is at least one of Ba, Ca, and Sr, 0<a<1, 0<b<1, a+b=1, c satisfies 0.80<c<1.10, 0<d1<1, 0<d2<1, 0<d3<1, 0≦d4<1, 0≦d5<1, d1+d2+d3+d4+d5=1, and e is a value indicating an oxygen deficiency or excess), b / (d3+d4+d5)≦1 a piezoelectric body made of a lead-free piezoelectric magnetic composition that satisfies the above requirements; A piezoelectric element comprising a base metal as a main component and an electrode in contact with the piezoelectric body.

2. 2. The piezoelectric element according to claim 1, wherein the molar ratio of Mn atoms to Nb atoms (Mn / Nb) contained in the main phase is 0.003 or more.

3. 3. The piezoelectric element according to claim 1, wherein the average particle size of the crystal grains of the alkali niobate perovskite oxide contained in the main phase is less than 6 μm.

4. The lead-free piezoelectric magnetic composition further comprises a compound represented by the composition formula A2 １－ｘ Ti １－ｘ Nb １＋ｘ O ５ (wherein element A2 is at least one alkali metal and satisfies 0≦x≦0.15), and a compound represented by the composition formula A3Ti ３ NbO ９ 4. The piezoelectric element according to claim 1, comprising a subphase made of one of the compounds represented by the formula: (wherein element A3 is at least one kind of alkali metal).

5. The piezoelectric element according to claim 1 , wherein the piezoelectric body and the electrode are alternately stacked.

6. Composition formula (A1 ａ M1 ｂ ) ｃ (Nb ｄ１ Mn ｄ２ Ti ｄ３ Zr ｄ４ Hf ｄ５ ) O ３＋ｅ a calcination step of mixing and firing raw materials of a lead-free piezoelectric magnetic composition containing a main phase made of an alkali niobate perovskite-type oxide represented by the following formula (wherein element A1 is at least one alkali metal, element M1 is at least one of Ba, Ca, and Sr, 0<a<1, 0<b<1, a+b=1, c satisfies 0.80<c<1.10, 0<d1<1, 0<d2<1, 0<d3<1, 0≦d4<1, 0≦d5<1, d1+d2+d3+d4+d5=1, and e is a value indicating oxygen deficiency or excess), and satisfying b / (d3+d4+d5)≦1, to obtain a calcined powder; a molding step of preparing a molded body containing the calcined powder; an electrode forming step of forming an electrode layer containing a base metal as a main component on the molded body; and co-firing the compact and the electrode layer in a reducing atmosphere.

7. 7. The method for producing a piezoelectric element according to claim 6, wherein in the calcination step, a molar ratio of Mn atoms to Nb atoms (Mn / Nb) contained in the raw material mixture is 0.005 or more.

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