Piezoelectric ceramic and piezoelectric element

Abstract

The piezoelectric ceramic according to the present disclosure includes, as a main component, a sodium potassium niobate-based composition. The composition is represented by general formula (1). General formula (1): {(K1-a-bNaaLib)1-c-dA1cA2d} x {(Nb1-e- fTaeSbf)1-g-hB1gB2h}O3. Further, the piezoelectric ceramic according to the present disclosure contains, with respect to 100 parts by mass of the abovementioned composition, Mn in the amount of 0.05 to 3.50 parts by mass in terms of MnO2.

Description

Piezoelectric ceramics and piezoelectric elements

[0001] The present disclosure relates to piezoelectric ceramics and piezoelectric elements.

[0002] Conventionally, PZT (lead zirconate titanate) based materials and PT (lead titanate) based materials have been used for parts that require piezoelectric properties. However, in recent years, there has been a growing movement to restrict the use of lead from the viewpoint of protecting the global environment, and there are high expectations for lead-free piezoelectric materials, and research and development is being actively carried out. Patent Document 1 describes a piezoelectric material with a perovskite structure (general formula ABO ３ ) an alkali niobate-based piezoelectric material in which an alkali metal is arranged at the A site and niobium is arranged at the B site is shown.

[0003] Japanese Patent Application Laid-Open No. 2006-028001

[0004] The piezoelectric ceramic of the present disclosure is a piezoelectric ceramic containing a potassium sodium niobate-based composition as a main component, and the composition is represented by the following general formula (1): {(K １－ａ－ｂ Na a Li ｂ ) １－ｃ－ｄ A1 ｃ A2 ｄ}x{(Nb １－ｅ－ｆ Ta ｅ Sb ｆ ) １－ｇ－ｈ B1 ｇ B2 ｈ O ３ ... (1) A1 is one or more elements selected from Ca, Sr, and Ba. A2 is one or more elements selected from La, Nd, Sm, and Bi. B1 is one or more elements selected from Ti, Zr, Hf, and Sn. B2 is one or more elements selected from Fe, Co, Ni, Cu, and Zn. a to h and x respectively satisfy the conditions of 0.30≦a≦0.65, 0.02≦b≦0.07, 0.0005≦c≦0.03, 0.0002≦d≦0.01, 0.03≦e≦0.16, 0.02≦f≦0.10, 0.003≦g≦0.03, 0.0001≦h≦0.03, and 0.95≦x≦1.03. For 100 parts by mass of the composition, Mn was added to MnO ２The content is 0.05 parts by mass or more and 3.50 parts by mass or less in terms of the total amount of the hydroxybenzoates.

[0005] FIG. 1 is a schematic diagram showing a cross section of the piezoelectric ceramic according to this embodiment.

[0006] Hereinafter, embodiments for implementing the piezoelectric ceramic and piezoelectric element according to the present disclosure (hereinafter referred to as "embodiments") will be described in detail. Note that the present disclosure is not limited to these embodiments. Furthermore, the embodiments can be appropriately combined within the scope of not causing any contradiction in the processing content. Furthermore, the same components in the following embodiments will be given the same reference numerals, and redundant explanations will be omitted.

[0007] Lead-free piezoelectric materials generally have inferior insulation reliability compared to PZT-based and PT-based materials. Insulation reliability refers to the resistance to degradation of insulation properties with use. For example, excellent insulation reliability means that insulation properties are maintained over a long period of time. However, in recent years, from the perspective of protecting the global environment, there has been a movement toward practical use of lead-free piezoelectric materials, even if they do not achieve the same insulation reliability as PZT-based and PT-based materials.

[0008] Despite these trends, for example, piezoelectric elements are naturally required to have excellent element performance, and therefore there is a demand for improved insulation reliability of lead-free piezoelectric materials.

[0009] The present disclosure has been made in view of such demands, and has as its object to provide a lead-free piezoelectric ceramic and a piezoelectric element that are excellent in insulation reliability.

[0010] The piezoelectric ceramic of the present disclosure contains potassium sodium niobate (KNN) and Mn as an additive. Potassium sodium niobate is the main component of the piezoelectric ceramic. In the present disclosure, the main component refers to the proportion of sodium in 100% by mass of all components constituting the piezoelectric ceramic. ２ O, potassium to K ２ O, niobium Nb ２ O ５ The total of the converted values ​​of the components accounts for 90 mass % or more.

[0011] The piezoelectric ceramic of the present disclosure, which contains Mn in potassium sodium niobate (KNN), has superior insulation reliability compared to that of a material that does not contain Mn. Insulation reliability refers to the resistance to deterioration of insulation properties with use. Therefore, excellent insulation reliability means that insulation properties are maintained for a long period of time. In the present disclosure, insulation reliability is evaluated by the "DC degradation time," which will be described later.

[0012] Next, an example of the compounded composition of potassium sodium niobate (hereinafter referred to as "KNN composition") in the piezoelectric ceramic of the present disclosure will be described.

[0013] The KNN composition in the piezoelectric ceramic of the present disclosure is represented by the following general formula (1): １－ａ－ｂ Na a Li ｂ ) １－ｃ－ｄ A1 ｃ A2 ｄ}x{(Nb １－ｅ－ｆ Ta ｅ Sb ｆ ) １－ｇ－ｈ B1 ｇ B2 ｈ O ３ ... (1) Here, A1 is at least one element selected from the group consisting of Ca, Sr, and Ba. A2 is at least one element selected from the group consisting of La, Nd, Sm, and Bi. B1 is at least one element selected from the group consisting of Ti, Zr, Hf, and Sn. B2 is at least one element selected from the group consisting of Fe, Co, Ni, Cu, and Zn. In addition, a, b, c, d, e, f, g, h, and x are within the following ranges: 0.30≦a≦0.65, 0.02≦b≦0.07, 0.0005≦c≦0.03, 0.0002≦d≦0.01, 0.03≦e≦0.16, 0.02≦f≦0.10, 0.003≦g≦0.03, 0.0001≦h≦0.03, and 0.95≦x≦1.03. The KNN composition has a perovskite structure.

[0014] The composition range satisfied by a, b, c, d, e, f, g, h, and x represented by general formula (1) is a composition range that includes a boundary where the crystal structure changes, namely, a composition range in the vicinity of a so-called MPB (Morphototropic Phase Boundary) or in the vicinity of a PPT (Polymorphic Phase Transition).

[0015] In the general formula (1), a, b, c, d, e, f, g, h, and x satisfy the above ranges. Mn is MnO relative to 100 parts by mass of the KNN composition. ２ The piezoelectric ceramic of the present disclosure containing 0.05 parts by mass or more and 3.50 parts by mass or less in terms of the converted amount has excellent piezoelectric properties and excellent insulation reliability.

[0016] In terms of piezoelectric properties and insulation reliability, a may be 0.45≦a≦0.55, b may be 0.03≦b0.055, c may be 0.005≦c≦0.015, and d may be 0.001≦d≦0.005. Also, e may be 0.05≦e≦0.15, f may be 0.04≦f≦0.08, g may be 0.005≦g≦0.015, and h may be 0.0005≦h≦0.015. Furthermore, x may be 0.98≦x≦1.02. The ranges described here are composition ranges closer to those of MPB and PPT.

[0017] In the following, the characteristics of the piezoelectric ceramic of the present disclosure will be explained using the measured values ​​of the average crystal grain size, relative density, strain, Curie temperature, DC degradation time, and PPT of the piezoelectric element of the present disclosure evaluated in the examples described below. The measurement method and measurement results for each evaluation item will be described in detail below. Of the above measurement items, strain is an index showing the piezoelectric characteristics of the piezoelectric element, and DC degradation time is an index showing the insulation reliability of the piezoelectric element.

[0018] The piezoelectric ceramic of the present disclosure is a ceramic material containing Mn in an amount of MnO relative to 100 parts by mass of the KNN composition. ２The KNN composition contains 0.05 parts by mass or more and 3.50 parts by mass or less, calculated as Mn. When the KNN composition contains a desired amount of Mn, the insulating properties are improved, making it difficult for current to flow outside of specified locations during operation. Therefore, the piezoelectric ceramic of the present disclosure has high insulating properties.

[0019] In this case, Mn may be present in the form of a solid solution within the crystal grains of KNN, or may be present at the crystal grain boundaries.

[0020] Mn may exist as a crystal with MnO as the parent phase, or MnO ２ and Mn ３ O ４ Alternatively, Mn may exist in an amorphous phase rather than in a crystalline state.

[0021] The piezoelectric ceramic of the present disclosure may have a Curie temperature of 200°C or higher, and an electric-field-induced strain (ppm) of 550 × X / 3 (ppm) or higher, where X is a direct current electric field (kV / mm). Generally, a practical Curie temperature is 200°C or higher. The Curie temperature is an indicator of the limit temperature at which a piezoelectric element can be used. For example, when the direct current electric field is 3 kV / mm, if the electric-field-induced strain is 550 ppm and the Curie temperature is 200°C or higher, the piezoelectric ceramic can be said to have both a practical Curie temperature and excellent piezoelectric properties.

[0022] The piezoelectric ceramic of the present disclosure may have an average crystal grain size of 1.6 μm or less. Furthermore, the proportion of crystal grains with a grain size of 20 μm or more may be 0.3% or less. A piezoelectric ceramic with a small average crystal grain size and a small number of large crystal grains with a grain size of 20 μm or more has a large amount of crystal grain boundaries per unit volume, resulting in high insulation properties. Generally, in piezoelectric ceramics, the insulation resistance of the crystal grain boundaries is higher than the insulation resistance inside the crystal, so the more crystal grain boundaries there are, the better the insulation properties.

[0023] The piezoelectric ceramic of the present disclosure may have a relative density of 95% or more. Such a piezoelectric ceramic has a high density of sintered body, and the dense structure of the sintered body provides excellent mechanical strength, which in turn provides excellent insulating properties of the porcelain.

[0024] The piezoelectric ceramic of the present disclosure is a ceramic material having a KNN composition and MnO ２ In addition, when the piezoelectric ceramic of the present disclosure contains the contained elements described later, the KNN composition, MnO ２ The composition of the piezoelectric ceramic and the content of the contained elements can be confirmed by measurement using an X-ray fluorescence analyzer, an ICP (Inductively Coupled Plasma) emission spectrometer, or the like.

[0025] The piezoelectric ceramic of the present disclosure may contain at least one element selected from the group consisting of V, Cr, Y, Yb, and W. Specifically, the total content of each element, calculated as an oxide, may be 0.005 parts by mass or more and 0.5 parts by mass or less per 100 parts by mass of the KNN composition. A piezoelectric ceramic containing desired amounts of the aforementioned elements exhibits excellent piezoelectric properties and excellent insulation reliability.

[0026] The piezoelectric ceramic of the present disclosure may contain Ag. Specifically, the Ag content is 100 parts by mass of the KNN composition. ２ The content may be 0.05 parts by mass or more and 5.0 parts by mass or less in terms of O. By containing a predetermined amount of Ag, it becomes difficult for current to flow to places other than predetermined locations during operation, and therefore excellent insulating properties are achieved.

[0027] Ag may be present in the crystal grains of KNN as a solid solution or at the grain boundaries. By being present in the crystal grains of KNN as a solid solution, Ag can compensate for lattice defects of K, Na, and Li and suppress the generation of electrons and holes due to the lattice defects.

[0028] In addition, Ag present at the grain boundaries is Ag ２ It may exist as a crystal with O as the parent phase. ２The presence of Ag as a crystal with O as the parent phase suppresses the growth of the crystal grains that become the main phase during sintering of the piezoelectric ceramic, making it possible to obtain a piezoelectric ceramic having a main phase with a relatively small average crystal grain size. The smaller the crystal grain size, the greater the amount of crystal grain boundaries (here, regions other than the main phase) that occupy per unit volume, resulting in improved insulation properties. When the content of Ag is 100 parts by mass of the KNN composition, the amount of Ag is 100 parts by mass of the KNN composition. ２ A piezoelectric ceramic having an O content of 0.05 parts by mass or more and 5.0 parts by mass or less has excellent piezoelectric properties and insulating reliability.

[0029] The piezoelectric ceramic of the present disclosure may also contain Si. Specifically, the content of Si is SiO ２ The Si content may be 0.02 parts by mass or more and 1.0 parts by mass or less, calculated as Si content. By including a predetermined amount of Si, the insulating properties are improved, and it becomes difficult for current to flow to any place other than the predetermined place during operation. Therefore, by including a predetermined amount of Si, the piezoelectric ceramic exhibits excellent insulating properties.

[0030] Si may be present in the crystal grains of KNN as a solid solution or at the crystal grain boundaries. ２ It may exist as a crystal with a parent phase of SiO ２ The presence of SiO as a crystal matrix suppresses the growth of the crystal grains that form the main phase during sintering of the piezoelectric ceramic, making it possible to obtain a piezoelectric ceramic having a main phase with a relatively small average crystal grain size. The smaller the crystal grain size, the greater the amount of grain boundaries (here, regions other than the main phase) that occupy per unit volume, improving the insulating properties. ２ The presence of crystals with the parent phase makes the grain boundaries thicker (the spacing between the main phases becomes wider), and the grain boundary resistance increases. Therefore, the insulation resistance of the piezoelectric ceramic also increases. When the Si content is 100 parts by mass of the KNN composition, the SiO ２ A piezoelectric ceramic having a content of 0.02 parts by mass or more and 1.0 parts by mass or less in terms of the total mass is excellent in piezoelectric properties and insulation reliability.

[0031] The piezoelectric ceramic of the present disclosure may contain halogen elements F and Cl. In such a case, for example, the total content of F and Cl may be 0.0005 mol% or more and 0.01 mol% or less per mol of the KNN composition. The inclusion of halogen elements F and Cl improves the sinterability of the sintered body. The content of F and Cl can be confirmed, for example, by measuring a powder obtained by pulverizing the piezoelectric ceramic as a sample using ion chromatography.

[0032] The piezoelectric ceramic of the present disclosure may contain P and S. In such a case, for example, the total content of P and S may be 0.0005 mol% or more and 0.01 mol% or less per mol of the KNN composition. The inclusion of P and S, which are third-period elements, improves the sinterability of the sintered body. The P and S contents can be confirmed by measuring a powder obtained by pulverizing the piezoelectric ceramic using an X-ray fluorescence analyzer or an ICP atomic emission spectrometer.

[0033] Fig. 1 is a schematic diagram showing a cross section of a piezoelectric ceramic according to this embodiment. The piezoelectric ceramic of the present disclosure may include a portion in which the density of Li is higher than that of other ceramics. Specifically, the "portion in which the density of Li is higher than that of other ceramics" refers to a portion (second portion 2) in which the composition ratio of Li in the KNN composition of general formula (1) is higher than that of the grain structure (first portion 1) that forms the main phase of the piezoelectric ceramic of the present disclosure, as shown in Fig. 1, and which appears speckled when the cross section of the piezoelectric ceramic is observed.

[0034] By having the second portion 2, the piezoelectric ceramic can deform due to the flexibility characteristic of Li when the piezoelectric ceramic expands and contracts, thereby dispersing the stress generated in the piezoelectric ceramic. Therefore, the piezoelectric ceramic has excellent durability. Furthermore, when the second portion 2 is observed in a plan view, the area ratio of the second portion 2 to the planar region observed may be, for example, 30% or less. Since the second portion 2 has a lower insulation resistance than other ceramic portions, a piezoelectric ceramic having a small proportion of the second portion 2 has excellent insulation properties while maintaining durability.

[0035] For example, the cross section of the piezoelectric ceramic sintered body can be photographed with a scanning electron microscope (SEM) at 2,000 to 20,000 magnifications, and the surface area photographed can be analyzed to determine the area ratio occupied by the speckled portions in a plan view. Furthermore, speckled portions can also be confirmed by analyzing the cross section of the piezoelectric ceramic with a time-of-flight mass meter using time-of-flight secondary ion mass spectrometry (TOF-SIMS).

[0036] The piezoelectric ceramic of the present disclosure may have a PPT of −50° C. or higher and 70° C. or lower. In general, the piezoelectric properties of a piezoelectric ceramic are high near the boundary between crystalline phases, and therefore such a piezoelectric ceramic has excellent piezoelectric properties at temperatures near room temperature.

[0037] <Production Method> Next, an example of a method for producing a piezoelectric element using the piezoelectric ceramic of the present disclosure will be described. ２ CO ３ , NaHCO ３、 K ２ CO ３ , KHCO ３、 and Li ２ CO ３ Carbonates such as CuO, ZnO, Nb ２ O ５ , Ta ２ O ５ , Sb ２ O ３ , TiO ２ , ZrO ２ , HfO ２ , SnO ２ , Bi ２ O ３ , MnO ２ and SrZrO ３ The raw materials are not limited to these, and metal salts such as nitrates that produce oxides upon firing may also be used.

[0038] In the KNN composition represented by the general formula (1), A1 is at least one element selected from the group consisting of Ca, Sr, and Ba, A2 is at least one element selected from the group consisting of La, Nd, Sm, and Bi, B1 is at least one element selected from the group consisting of Ti, Zr, Hf, and Sn, and B2 is at least one element selected from the group consisting of Fe, Co, Ni, Cu, and Zn. The above-mentioned raw materials are used to adjust the content within a predetermined range, and Mn is added to 100 parts by mass of the KNN composition by the amount of MnO. ２ The weight is weighed out so that the equivalent weight is 0.05 parts by mass or more and 3.50 parts by mass.

[0039] The weighed raw material powders, an appropriate amount of solvent, and an appropriate amount of media are sealed in a cylindrical pot and stirred and mixed (primary blending) for 10 to 80 hours using a ball mill method. After stirring and mixing, the solvent is evaporated to obtain a mixed powder in which the raw material powders are thoroughly mixed. The solvent may be, for example, an organic solvent. Examples of organic solvents that can be used include ethanol, isopropanol, and acetone. The solvent may also be pure water (deionized water). Stabilized zirconia balls or the like are used as media.

[0040] The resulting mixed powder is calcined at 700°C to 1100°C for 1 to 10 hours to obtain a calcined body, which is then pulverized by a ball mill (secondary blending) to obtain a calcined powder.

[0041] In the piezoelectric ceramic of the present disclosure, raw materials for oxides of some of the elements represented by general formula (1) and additional elements such as Mn, Ag, and Si may be added in the secondary blending instead of the primary blending described above. In such a case, the total amount of oxides added in the secondary blending together with the pre-sintered body may be 10 mol % or less relative to the pre-sintered body.

[0042] The resulting pre-sintered powder is wet-mixed with an organic binder, a dispersant, and pure water or an organic solvent to obtain a granulated powder, which is then molded by a known molding method such as press molding or tape molding to obtain a ceramic green sheet.

[0043] The resulting ceramic green sheets are stacked and cut to a predetermined shape, and then heated to approximately 300°C to 500°C to remove the binder. This is then fired in an air atmosphere at a temperature range of 850°C to 1150°C for 2 to 16 hours to obtain a piezoelectric ceramic. The resulting piezoelectric ceramic has, for example, a first surface and a second surface located opposite the first surface. A first electrode is then placed on the first surface of the resulting piezoelectric ceramic, and a second electrode is placed on the second surface, thereby obtaining a piezoelectric element.

[0044] Piezoelectric elements can also be stacked to obtain a laminate. Specifically, a conductive paste is first prepared by adding a binder and a plasticizer to a metal powder, such as an Ag-Pd alloy or Ni, which will become the internal electrodes, and mixing them. This conductive paste is then printed onto the ceramic green sheets using a screen printing method. Next, a plurality of printed sheets with the conductive paste printed thereon are stacked, and a plurality of ceramic green sheets without the conductive paste printed on both ends in the stacking direction are stacked to obtain a laminated molded body. This laminated molded body is then subjected to a binder removal treatment at a predetermined temperature and then fired to obtain a laminated body.

[0045] <Evaluation Methods> Next, methods for evaluating the average crystal grain size, relative density, strain, Curie temperature, DC degradation time, and PPT of the piezoelectric ceramic of the present disclosure will be described.

[0046] (1) Average crystal grain size / proportion of crystal grains of 20 μm or more The average crystal grain size (μm) can be calculated by photographing the cross section of a piezoelectric ceramic sintered body with a SEM (scanning electron microscope) at 2,000 to 20,000 magnifications and analyzing the image of the photographed cross-sectional region. In addition, by comparing the total number of crystal grains in the photographed cross-sectional region with the number of crystal grains with a grain size of 20 μm or more, for example, the proportion of large crystal grains with a grain size of 20 μm or more can be calculated.

[0047] (2) Relative Density The relative density can be calculated as Archimedes density / theoretical density. The Archimedes density is the density measured by the immersion method. Theoretical density is the density calculated from the lattice constant and elemental composition obtained by X-ray analysis.

[0048] (3) Strain The strain (ppm) can be obtained by applying a DC electric field of 3 kV / mm along the axial direction of the piezoelectric element and measuring the amount of elongation ΔS generated along the axial direction with a contact displacement meter. The value of strain is calculated by dividing the axial dimension of the piezoelectric element by S ０ When this is the case, ΔS / S ０ The piezoelectric element used for measurement may be, for example, a disk-shaped sintered body having a diameter of 5 to 15 mm and an axial thickness of 0.2 to 2 mm, with electrodes containing Ag as the main component formed on both sides. Note that a non-contact laser displacement meter may be used to measure the elongation amount ΔS.

[0049] (4) Curie temperature Curie temperature T Ｃ The Curie temperature (°C) can be determined by measuring the temperature and capacitance of the piezoelectric element while placing the piezoelectric element in a furnace and heating it to 400°C, and then lowering the temperature at a rate of 0.5 to 5°C / min, and the temperature at which the measured capacitance reaches its peak can be determined as the Curie temperature.

[0050] (5) DC Degradation Time The DC degradation time (Hr) is the time T required for the measured current value to become 10 times the reference current value (hereinafter referred to as the “reference current value”) measured 0.1 Hr after the start of application of the electric field when a DC electric field of 3 kV / mm is continuously applied to a piezoelectric element whose temperature is controlled at 170°C. Ｂ Measure (T Ｂ -0.1).

[0051] (6) PPT The temperature change of the resonant frequency of a piezoelectric element is measured in the element temperature range of -70 to 170°C, and the temperature at which the resonant frequency is lowest can be calculated as the PPT from the measured curve.

[0052] Piezoelectric element samples with the various compositions shown in Tables 1 to 4 were fabricated using the firing temperatures shown in Tables 1 and 2. Then, using the evaluation methods described above, the average crystal grain size, the proportion of crystal grains 20 μm or larger, relative density, strain, Curie temperature, DC degradation time, and PPT were measured. Tables 5 and 6 show the measurement results. Of the fabricated samples, Samples No. 1 to No. 3 are comparative examples, and Samples No. 4 to No. 46 are working examples. The fabricated piezoelectric elements were single-plate piezoelectric elements including a pair of electrodes fabricated by the piezoelectric element manufacturing method described above.

[0053]

[0054]

[0055]

[0056]

[0057]

[0058]

[0059] Samples No. 1 and No. 2, which are comparative examples, differ from Samples No. 4 to No. 46, which are examples, in that they do not contain A1, A2, B1, or Mn. Also, Sample No. 3, which is a comparative example, differs from Samples No. 4 to No. 46, which are examples, in that it does not contain A2 or Mn.

[0060] The average crystal grain size of Samples No. 1 to No. 3, which are comparative examples, was 2.5 μm or more and 18 μm or less. In contrast, the average crystal grain size of Samples No. 4 to No. 46, which are examples, was all 1.6 μm or less (0.7 μm or more and 1.6 μm or less). As such, it can be seen that Samples No. 4 to No. 46, which are examples, all have smaller average crystal grain sizes than Samples No. 1 to No. 3, which are comparative examples.

[0061] Furthermore, the proportion of crystal grains with a grain size of 20 μm or more in Samples No. 1 to No. 3, which are comparative examples, was 2% to 9%. In contrast, the proportion of crystal grains with a grain size of 20 μm or more in Samples No. 4 to No. 46, which are examples, was 0.3% or less. As such, it can be seen that Samples No. 4 to No. 46, which are examples, all have a smaller proportion of crystal grains with a grain size of 20 μm or more than that of Samples No. 1 to No. 3, which are comparative examples. Specifically, for example, Samples No. 4 to No. 19, No. 21 to No. 42, No. 45, and No. 46 have a proportion of crystal grains with a grain size of 20 μm or more of less than 0.1%.

[0062] The relative densities of Samples No. 1 to No. 3, which are comparative examples, were 92% or more and 94% or less. In contrast, the relative densities of Samples No. 4 to No. 46, which are examples, were all 95% or more (95% or more and 97% or less). As such, it can be seen that Samples No. 4 to No. 46, which are examples, all have higher relative densities than Samples No. 1 to No. 3, which are comparative examples.

[0063] The Curie temperature of Sample No. 2, which is a comparative example, was 170°C. The Curie temperatures of Samples No. 4 to No. 46, which are examples, were all 220°C or higher and 340°C or lower. As such, it can be seen that the measured Curie temperatures of all the examples exceeded 200°C, which is an index of a practical Curie temperature.

[0064] The PPT of Sample No. 2, which is a comparative example, was −60° C. The PPT of Samples No. 4 to No. 46, which are examples, was −50° C. or higher and 70° C. or lower.

[0065] The strain of Samples No. 1 to No. 3, which are comparative examples, when a high electric field was applied was 380 ppm or more and 540 ppm or less. In contrast, the strain of Samples No. 4 to No. 46, which are examples, when a high electric field was applied was 660 ppm or more and 1080 ppm or less. As such, it can be seen that Samples No. 4 to No. 46, which are examples, all exhibit larger strain when a high electric field was applied than Samples No. 1 to No. 3, which are comparative examples.

[0066] It was not possible to measure the DC degradation time when a high electric field was applied to Samples No. 2 and 3, which are comparative examples, and the DC degradation time when a high electric field was applied to Sample No. 1 was 0.2 hours. In contrast, the DC degradation times when a high electric field was applied to Samples No. 4 to No. 46, which are examples, were all 25 hours or more and 360 hours or less. As such, it can be seen that Samples No. 4 to No. 46, which are examples, all had longer DC degradation times when a high electric field was applied than Samples No. 1 to 3, which are comparative examples.

[0067] Next, a sample containing V was prepared using Sample No. 44 as a base (composition, firing temperature), and the DC deterioration time was measured. ２ O ５ The measurement results of the content converted into DC deterioration time are shown in Table 7.

[0068]

[0069] V to V ２ O ５ It can be seen that Samples Nos. 47 to 49, in which the content converted to DC was 0.0005 parts by mass or more and 0.5 parts by mass or less, had a long DC deterioration time and were excellent in insulation reliability.

[0070] Furthermore, when the strain of Samples Nos. 47 to 49 was measured, it was found to be comparable to that of Sample No. 44, demonstrating that they have excellent piezoelectric properties and excellent insulation reliability.

[0071] In addition, Cr (Cr ２ O ３ ), Y(Y ２ O ３ ), Yb(Yb ２ O ３ ) and W(WO ３ ) were also prepared, and DC deterioration time was checked by preparing samples containing them alone and in combination. When the content was 0.005 parts by mass or more and 0.5 parts by mass or less, the DC deterioration time value was long, and it was found that the insulation reliability was excellent. ２ O ３ , Y is Y ２ O ３ , Yb is Yb ２ O ３ , W is WO ３is converted into

[0072] Next, a sample containing Ag was prepared using Sample No. 44 as a base (composition, firing temperature), and the DC deterioration time was measured. ２ The measurement results of the content converted to O and the DC deterioration time are shown in Table 8.

[0073]

[0074] Ag to Ag ２ Samples Nos. 51 to 53, in which the content converted to O was 0.05 parts by mass or more and 5.0 parts by mass or less, had long DC deterioration times, indicating that they were excellent in insulation reliability.

[0075] Furthermore, when the strain of Samples Nos. 51 to 53 was measured, it was found to be comparable to that of Sample No. 44, demonstrating that they have excellent piezoelectric properties and excellent insulation reliability.

[0076] Furthermore, although not shown in the table, when the average crystal grain size of Samples Nos. 51 to 53 was confirmed, it was found that the values ​​were smaller than that of Sample No. 44, which indicates that the inclusion of Ag allows for a lower firing temperature.

[0077] Next, a sample containing Si was prepared using Sample No. 44 as a base (composition, firing temperature), and the DC deterioration time was measured. ２ The measurement results of the content converted into DC deterioration time are shown in Table 9.

[0078]

[0079] Si to SiO ２ It can be seen that Samples No. 55 to 57, in which the content converted to DC was 0.02 parts by mass or more and 1.0 parts by mass or less, had a long DC deterioration time and were excellent in insulation reliability.

[0080] Furthermore, when the strain of Samples Nos. 55 to 57 was measured, it was found to be comparable to that of Sample No. 44, demonstrating that they have excellent piezoelectric properties and excellent insulation reliability.

[0081] Next, samples containing F and Cl were prepared using Sample No. 44 as a base (composition, firing temperature), and the DC deterioration time was measured. The F and Cl contents and the DC deterioration time measurement results are shown in Table 10.

[0082]

[0083] Samples Nos. 59 to 61, in which the total content of F and Cl was 0.0005 mol % or more and 0.01 mol % or less, showed a long DC deterioration time, indicating excellent insulation reliability.

[0084] Furthermore, when the strain of Samples Nos. 59 to 61 was measured, it was found to be comparable to that of Sample No. 44, demonstrating that they have excellent piezoelectric properties and excellent insulation reliability.

[0085] Next, samples containing P and S were prepared using Sample No. 44 as a base (composition, firing temperature), and the DC deterioration time was measured. The P and S contents and the DC deterioration time measurement results are shown in Table 11.

[0086]

[0087] Samples Nos. 63 to 65, in which the total content of P and S was 0.0005 mol % or more and 0.01 mol % or less, exhibited long DC deterioration times, indicating excellent insulation reliability.

[0088] Furthermore, when the strain of Samples Nos. 63 to 65 was measured, it was found to be comparable to that of Sample No. 44, demonstrating that they have excellent piezoelectric properties and excellent insulation reliability.

[0089] The disclosed embodiments should be considered in all respects as illustrative and not restrictive. Indeed, the above-described embodiments may be embodied in various forms. Furthermore, the above-described embodiments may be omitted, substituted, or modified in various ways without departing from the scope and spirit of the appended claims.

[0090] The present technology can be configured as follows: (1) A piezoelectric ceramic mainly composed of a potassium sodium niobate-based composition, wherein the composition is represented by the following general formula (1): {(K １－ａ－ｂ Naa Li ｂ ) １－ｃ－ｄ A1 ｃ A2 ｄ}x{(Nb １－ｅ－ｆ Ta ｅ Sb ｆ ) １－ｇ－ｈ B1 ｇ B2 ｈ O ３ ... (1) In the general formula (1), A1 is one or more elements selected from Ca, Sr, and Ba, A2 is one or more elements selected from La, Nd, Sm, and Bi, B1 is one or more elements selected from Ti, Zr, Hf, and Sn, B2 is one or more elements selected from Fe, Co, Ni, Cu, and Zn, and a to x are each in the range of 0.30≦a≦0.65, 0.02≦b≦0.07, 0.0005≦c≦0.03, 0.0002≦d≦0.01, 0.03≦e≦0.16, 0.02≦f≦0.10, 0.003≦g≦0.03, 0.0001≦h≦0.03, The condition of 0.95≦x≦1.03 is satisfied, and Mn is added to 100 parts by mass of the composition in an amount of MnO ２ (2) A piezoelectric ceramic according to (1) above, having a Curie temperature of 200°C or higher and an electric field-induced strain (ppm) of 550×X / 3 (ppm) or higher, where X is a direct current electric field (kV / mm). (3) A piezoelectric ceramic according to (1) or (2) above, having an average crystal grain size of 1.6 μm or lower, and having a proportion of crystal grains having a grain size of 20 μm or higher of 0.3% or lower. (4) A piezoelectric ceramic according to any one of (1) to (3) above, having a relative density of 95% or higher. (5) A piezoelectric ceramic according to any one of (1) to (4) above, containing at least one element selected from the group consisting of V, Cr, Y, Yb, and W, and having a total content of each element, calculated as an oxide, of 0.005 to 0.5 parts by mass per 100 parts by mass of the composition. (6) Ag is added to 100 parts by mass of the composition. ２(7) The piezoelectric ceramic according to any one of (1) to (5) above, containing 0.05 parts by mass or more and 5.0 parts by mass or less of Si in the form of SiO relative to 100 parts by mass of the composition. ２ (1) The piezoelectric ceramic according to any one of (1) to (6), containing 0.02 parts by mass or more and 1.0 parts by mass or less, calculated as a Li content of the first portion of the first grain structure. (8) The piezoelectric ceramic according to any one of (1) to (7), containing 0.0005 mol% or more and 0.01 mol% or less of F and Cl in total relative to 1 mol of the composition. (9) The piezoelectric ceramic according to any one of (1) to (8), containing 0.0005 mol% or more and 0.01 mol% or less of P and S in total relative to 1 mol of the composition. (10) The piezoelectric ceramic according to any one of (1) to (9), having: a first portion which is a grain structure forming a main phase; and a second portion which is a grain structure having a higher Li density than the first portion. (11) A piezoelectric element comprising: the piezoelectric ceramic according to any one of (1) to (10); and a plurality of electrodes including a first electrode located on a first surface of the piezoelectric ceramic and a second electrode located on a second surface of the piezoelectric ceramic.

[0091] 1 1st part 2 2nd part

Claims

1. A piezoelectric ceramic mainly composed of a potassium sodium niobate-based composition, wherein the composition is represented by the following general formula (1): {(K １－ａ－ｂ Na a Li ｂ ) １－ｃ－ｄ A1 ｃ A2 ｄ }x{(Nb １－ｅ－ｆ Ta ｅ Sb ｆ ) １－ｇ－ｈ B1 ｇ B2 ｈ O ３ ... (1) In the general formula (1), A1 is one or more elements selected from Ca, Sr, and Ba, A2 is one or more elements selected from La, Nd, Sm, and Bi, B1 is one or more elements selected from Ti, Zr, Hf, and Sn, B2 is one or more elements selected from Fe, Co, Ni, Cu, and Zn, and a to x are each in the range of 0.30≦a≦0.65, 0.02≦b≦0.07, 0.0005≦c≦0.03, 0.0002≦d≦0.01, 0.03≦e≦0.16, 0.02≦f≦0.10, 0.003≦g≦0.03, 0.0001≦h≦0.03, The condition of 0.95≦x≦1.03 is satisfied, and Mn is added to 100 parts by mass of the composition in an amount of MnO ２ The piezoelectric ceramic contains, in terms of a content of 0.05 parts by mass or more and 3.50 parts by mass or less.

2. A piezoelectric ceramic according to claim 1, having a Curie temperature of 200°C or higher and an electric field-induced strain (ppm) of 550 x X / 3 (ppm) or higher, where X is a DC electric field (kV / mm).

3. A piezoelectric ceramic according to claim 1 or 2, wherein the average crystal grain size is 1.6 μm or less, and the proportion of crystal grains with a grain size of 20 μm or more is 0.3% or less.

4. A piezoelectric ceramic according to any one of claims 1 to 3, having a relative density of 95% or more.

5. A piezoelectric ceramic according to any one of claims 1 to 4, which contains at least one element selected from the group consisting of V, Cr, Y, Yb, and W, and the total content of these elements, calculated as oxides, per 100 parts by mass of the composition is 0.005 parts by mass or more and 0.5 parts by mass or less.

6. For 100 parts by mass of the composition, Ag is added ２ 6. The piezoelectric ceramic according to claim 1, containing 0.05 parts by mass or more and 5.0 parts by mass or less in terms of O.

7. For 100 parts by mass of the composition, Si is added to SiO ２ The piezoelectric ceramic according to any one of claims 1 to 6, containing 0.02 parts by mass or more and 1.0 parts by mass or less in terms of the amount of arsenic.

8. A piezoelectric ceramic according to any one of claims 1 to 7, which contains F and Cl in a total amount of 0.0005 mol % to 0.01 mol % per 1 mol of said composition.

9. A piezoelectric ceramic according to any one of claims 1 to 8, which contains P and S in a total amount of 0.0005 mol % to 0.01 mol % per 1 mol of said composition.

10. The piezoelectric ceramic according to claim 1, comprising: a first portion which is a grain structure forming a main phase; and a second portion which is a grain structure having a higher Li density than the first portion.

11. A piezoelectric element comprising: a piezoelectric ceramic according to any one of claims 1 to 10; and a plurality of electrodes including a first electrode located on a first surface of the piezoelectric ceramic and a second electrode located on a second surface of the piezoelectric ceramic.

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