Lead-free piezoelectric ceramic composition

Abstract

To provide a lead-free piezoelectric porcelain composition capable of enhancing piezoelectric properties.SOLUTION: A lead-free piezoelectric porcelain composition comprises: a main phase containing a perovskite type oxide; and an auxiliary phase containing a manganese (Mn) compound. The maximum particle diameter of the manganese (Mn) compound is more than 0 μm and less than 33 μm.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present disclosure relates to a lead-free piezoelectric ceramic composition.

Background Art

[0002] Many of the piezoelectric ceramics (piezoelectric ceramics) that have been mass-produced conventionally are composed of PZT-based (lead zirconate titanate-based) materials and contain lead. However, in recent years, in order to eliminate the adverse effects of lead on the environment, the development of lead-free piezoelectric ceramics has been desired. Such a material for lead-free piezoelectric ceramics (referred to as "lead-free piezoelectric ceramic composition") is disclosed, for example, in Patent Document 1. In the ceramic composition of Patent Document 1, manganese oxide exists inside the ceramic sintered body as a heterogeneous phase with respect to the matrix phase containing an alkali niobate-based perovskite-type oxide.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, in the ceramic composition of Patent Document 1, although manganese oxide is added to the ceramic sintered body, the dielectric loss is relatively large, so the maximum phase angle is small and the polarization is insufficient. Therefore, with such a ceramic composition, sufficient piezoelectric properties cannot be obtained. Therefore, further improvement of piezoelectric properties is required in the ceramic composition. The present disclosure has been made in view of the above circumstances, and an object thereof is to improve piezoelectric properties. The present disclosure can be realized in the following forms.

Means for Solving the Problems

[0005] 〔1〕A main phase containing a perovskite-type oxide, A secondary phase containing a manganese (Mn) compound, and including a lead-free piezoelectric ceramic composition, wherein the maximum particle diameter of the manganese (Mn) compound is greater than 0 μm and less than 33 μm.

[0006] 〔2〕The lead-free piezoelectric ceramic composition according to 〔1〕, wherein the perovskite-type oxide is an alkali-based perovskite-type oxide.

[0007] 〔3〕The lead-free piezoelectric ceramic composition according to 〔2〕, wherein the alkali-based perovskite-type oxide contains niobium (Nb).

[0008] 〔4〕The alkali-based perovskite-type oxide has a composition formula (K a Na b Li c M1 d ) e (M2 f )O g (Element M1 is one or more of calcium (Ca), strontium (Sr), and barium (Ba); element M2 is one or more containing at least niobium (Nb) or tantalum (Ta) among niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf); a + b + c + d = 1, a + b + c ≠ 0, 0.80 ≦ e ≦ 1.10, f = 1, and g is an arbitrary value that can maintain the perovskite-type crystal structure). The lead-free piezoelectric ceramic composition according to 〔2〕 or 〔3〕.

[0009] 〔5〕The lead-free piezoelectric ceramic composition according to any one of 〔1〕 to 〔4〕, wherein the content ratio of manganese (Mn) is greater than 0 mol% and less than or equal to 5 mol%.

[0010] 〔6〕The lead-free piezoelectric ceramic composition according to any one of 〔1〕 to 〔5〕, wherein the manganese (Mn) compound contains a compound represented by the composition formula Mn3O4.

Advantages of the Invention

[0011] The lead-free piezoelectric ceramic composition of the present disclosure can improve piezoelectric properties.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0013] Hereinafter, the present disclosure will be described in detail. In this specification, for a description using "~" for a numerical range, unless otherwise specified, it includes the lower limit value and the upper limit value. For example, in the description of "10~20", both the lower limit value "10" and the upper limit value "20" are included. That is, "10~20" has the same meaning as "10 or more and 20 or less".

[0014] 1. Lead-free piezoelectric ceramic composition The lead-free piezoelectric ceramic composition of this embodiment does not contain Pb (lead), and includes a main phase containing a perovskite-type oxide and a sub-phase containing a manganese (Mn) compound.

[0015] (1) Main phase The perovskite-type oxide is preferably an alkaline perovskite-type oxide containing an alkali metal. The perovskite-type oxide is more preferably an alkaline perovskite-type oxide containing Nb (niobium).

[0016] As the perovskite-type oxide, those represented by the following compositional formula ((1) formula) are preferably exemplified. Element M1 is one or more of calcium (Ca), strontium (Sr), and barium (Ba). Element M2 is one or more containing at least niobium (Nb) or tantalum (Ta) among niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf). For example, element M2 is niobium (Nb) and one or more of titanium (Ti), zirconium (Zr), and hafnium (Hf). For example, element M2 is tantalum (Ta) and one or more of titanium (Ti), zirconium (Zr), and hafnium (Hf). For example, element M2 is niobium (Nb), tantalum (Ta), and one or more of titanium (Ti), zirconium (Zr), and hafnium (Hf). The value of g is any value that can maintain the perovskite-type crystal structure. That is, the amount of O atoms is such that the perovskite-type crystal structure can be maintained. (K a Na b Li c M1 d ) e (M2 f )O g …(1)

[0017] In the above compositional formula (1), the respective element ratios are preferably in the following ranges from the viewpoint of the electrical characteristics or piezoelectric characteristics (particularly piezoelectric constant d 33 ) of the lead-free piezoelectric ceramic composition. 0.090 ≦ a ≦ 0.660, 0.270 ≦ b ≦ 0.840, 0.000 ≦ c ≦ 0.050, 0.010 ≦ d ≦ 0.110, 0.800 ≦ e ≦ 1.100, 0.960 ≦ f ≦ 1.060, and the value of g is any value that can maintain the perovskite-type crystal structure a + b + c + d = 1 a + b + c ≠ 0

[0018] In the above compositional formula (1), the respective element ratios are more preferably in the following ranges. 0.210 ≤ a ≤ 0.590, 0.340 ≤ b ≤ 0.720, 0.010 ≤ c ≤ 0.040, 0.020 ≤ d ≤ 0.090, 0.850 ≤ e ≤ 1.050, 0.970 ≤ f ≤ 1.040, and the value of g can be any value that can maintain the perovskite crystal structure. a + b + c + d = 1 a + b + c ≠ 0

[0019] In the above composition formula (1), the elemental ratios of each are more preferably in the following ranges. 0.340 ≤ a ≤ 0.530, 0.400 ≤ b ≤ 0.590, 0.015 ≤ c ≤ 0.030, 0.030 ≤ d ≤ 0.070, 0.900 ≤ e ≤ 1.000, 0.980 ≤ f ≤ 1.020, and the value of g can be any value that can maintain the perovskite crystal structure. a + b + c + d = 1 a + b + c ≠ 0

[0020] In the above composition formula (1), when M1 is barium (Ba) and calcium (Ca), the composition formula (1) is represented as the following composition formula (2). d = X1 + Y1. (K a Na b Li c Ba X1 Ca Y1 ) e (M2 f )O g …(2) The elemental ratio X1 of barium (Ba) is preferably in the range of 0.02 ≤ X1 ≤ 0.05. The elemental ratio Y1 of calcium (Ca) is preferably in the range of 0.01 ≤ X1 ≤ 0.05.

[0021] In the above composition formula (1), when M1 is calcium (Ca), the composition formula (1) is represented as the following composition formula (3). d = Y1. (K a Na b Li c Ca Y1 ) e (M2 f )Og …(3) The elemental ratio Y1 of calcium (Ca) is preferably in the range of 0.01 ≦ X1 ≦ 0.03.

[0022] In the above composition formula (1), when M1 is barium (Ba) and strontium (Sr), the composition formula (1) is represented as the following composition formula (4). d = X1 + Z1. (K a Na b Li c Ba X1 Sr Z1 ) e (M2 f )O g …(4) The elemental ratio X1 of barium (Ba) is preferably in the range of 0.04 ≦ X1 ≦ 0.06. The elemental ratio Z1 of strontium (Sr) is preferably in the range of 0.04 ≦ Z1 ≦ 0.06.

[0023] In the above composition formula (1), when M2 is niobium (Nb), zirconium (Zr), and titanium (Ti), the composition formula (1) is represented as the following composition formula (5). f = X2 + Y2 + Z2. (K a Na b Li c M1 d ) e (Nb X2 Zr Y2 Ti Z2 )O g …(5) The elemental ratio X2 of niobium (Nb) is preferably in the range of 0.80 ≦ X2 ≦ 1.0. The elemental ratio Y2 of zirconium (Zr) is preferably in the range of 0.02 ≦ X1 ≦ 0.06. The elemental ratio Z2 of titanium (Ti) is preferably in the range of 0.02 ≦ X1 ≦ 0.06.

[0024] In the above compositional formula (1), when M2 is niobium (Nb) and titanium (Ti), the compositional formula (1) is represented as the following compositional formula (6). f = X2 + Z2. (K a Na b Li c M1 d ) e (Nb X2 Ti Z2 )O g …(6) The elemental ratio X2 of niobium (Nb) is preferably in the range of 0.90 ≦ X2 ≦ 1.0. The elemental ratio Z2 of titanium (Ti) is preferably in the range of 0.01 ≦ X1 ≦ 0.03.

[0025] In the above compositional formula (1), when M2 is niobium (Nb) and zirconium (Zr), the compositional formula (1) is represented as the following compositional formula (7). f = X2 + Y2. (K a Na b Li c M1 d ) e (Nb X2 Zr Y2 )O g …(7) The elemental ratio X2 of niobium (Nb) is preferably in the range of 0.90 ≦ X2 ≦ 1.0. The elemental ratio Y2 of zirconium (Zr) is preferably in the range of 0.02 ≦ X1 ≦ 0.04.

[0026] (2) Secondary phase The lead-free piezoelectric ceramic composition of this embodiment contains a secondary phase containing a manganese (Mn) compound. More preferably, the secondary phase may contain a metal oxide. The manganese (Mn) compound preferably contains a compound represented by the compositional formula Mn3O4. The manganese (Mn) compound may contain compounds represented by the compositional formulas MnO, MnO2, Mn2O3, MnCO3, etc., and may also contain other metal elements such as Ti.

[0027] The maximum particle size of the manganese (Mn) compound is preferably greater than 0 μm and less than 33 μm. More preferably, the maximum particle size of the manganese (Mn) compound is greater than 0.2 μm and less than or equal to 11 μm. Even more preferably, the maximum particle size of the manganese (Mn) compound is greater than 0.5 μm and less than or equal to 5 μm.

[0028] The content ratio of manganese (Mn) in the lead-free piezoelectric ceramic composition is preferably greater than 0 mol% and less than or equal to 5 mol%. More preferably, the content ratio of manganese (Mn) in the lead-free piezoelectric ceramic composition is greater than 0.3 mol% and less than or equal to 4 mol%. Even more preferably, the content ratio of manganese (Mn) in the lead-free piezoelectric ceramic composition is greater than 0.6 mol% and less than or equal to 2.5 mol%.

[0029] FIG. 1 is an example of a flowchart showing a method for manufacturing a piezoelectric element according to an embodiment of the present disclosure. The first component and the second component produced below are mixed to form a main phase and a secondary phase. The first component is the main component contained in the main phase. The second component is a component different from the main phase.

[0030] In step T110, the raw materials of the first component are mixed. The first component is the main component contained in the main phase. In step T110, as the raw materials of the first component, the necessary ones are selected from among raw materials such as K2CO3 powder, Na2CO3 powder, Li2CO3 powder, CaCO3 powder, SrCO3 powder, BaCO3 powder, Nb2O5 powder, Ta2O5 powder, TiO2 powder, ZrO2 powder, MgO powder, Fe2O3 powder, CoO powder, ZnO powder, etc., and weighed according to the values of the coefficients (for example, a to f, i in the following composition formula (8) of the first component). Note that the values of the element ratios b, c, d, e are the values of the element ratios b, c, d, e in the above composition formula (1). (K a Na b Li c M1 d ) e (M2 f )O i …(8) Then, ethanol is added to the raw material powder and wet-mixed using a ball mill to obtain a slurry. The wet mixing using the ball mill is preferably carried out for 15 hours or more. In step T120, the mixed powder obtained by drying the slurry is calcined, for example, at 600°C to 1100°C for 1 hour to 10 hours in an air atmosphere to produce a calcined powder of the first component.

[0031] In step T130, the raw material mixing of the second component is carried out. The composition of the second component is preferably K 0.85 Ti 0.85 Nb 1.15 O5. Note that the composition of the second component may also be KTiNbO5, K 0.90 Ti 0.90 Nb 1.10 O5 or the like. As the raw materials of the second component, K2CO3 powder, Nb2O5 powder, and TiO2 powder are selected and weighed according to the value of the composition formula of the second component. Then, ethanol is added to these raw material powders and wet-mixed using a ball mill to obtain a slurry. The wet mixing using the ball mill is preferably carried out for 15 hours or more. In step T140, the mixed powder obtained by drying the slurry is calcined, for example, at 600°C to 1100°C for 1 hour to 10 hours in an air atmosphere to produce a calcined powder of the second component.

[0032] In Process T150, the first component, the second component, and Mn species (e.g., MnCO3, MnO, Mn2O3, MnO2, etc.) are weighed respectively, and a dispersant, a binder, and ethanol are added, followed by grinding and mixing in a ball mill to obtain a slurry. Incidentally, this slurry may be calcined once again and then ground and mixed. Thereafter, the slurry is dried, granulated, and, for example, uniaxially pressed at a pressure of 20 MPa to form into a desired shape. As an embodiment of the present disclosure, typical shapes of piezoelectric ceramics suitable for the composition are, for example, disk shape and column shape. Thereafter, for example, a CIP treatment (cold isostatic pressing treatment) is performed at a pressure of 150 MPa to obtain a formed body. In Process T160, the obtained formed body (CIP pressed body) is fired by holding it at 900 °C to 1300 °C for 1 hour to 10 hours in, for example, an air atmosphere to obtain a piezoelectric ceramic. The firing in Process T160 may be performed in an O2 atmosphere. Next, the piezoelectric ceramic is processed in Process T170 according to the dimensional accuracy required for the piezoelectric element. In Process T180, electrodes are attached to the thus obtained piezoelectric ceramic, and poling treatment is performed in Process T190.

[0033] The manufacturing method described above is an example, and various other processes and processing conditions for manufacturing a piezoelectric element can be used. For example, as shown in FIG. 1, the first component and the second component are separately generated in advance, and then the powders of both are mixed and fired. Instead, a piezoelectric ceramic composition may be manufactured by mixing and firing the raw materials containing the first component and the second component together. However, according to the manufacturing method of FIG. 1, since the compositions of the first component and the second component can be more strictly controlled, it is possible to increase the yield of the piezoelectric ceramic composition.

[0034] 2. Piezoelectric Element FIG. 2 is a perspective view showing a piezoelectric element as an embodiment of the present disclosure. This piezoelectric element 200 has a configuration in which electrodes 301 and 302 are attached to the upper surface and the lower surface of a disk-shaped piezoelectric ceramic 100. Incidentally, as the piezoelectric element, piezoelectric elements with various other shapes and configurations can be formed.

[0035] 3. Use of Lead-Free Piezoelectric Ceramic Composition and Piezoelectric Element The lead-free piezoelectric ceramic composition and piezoelectric element according to the embodiments of the present disclosure can be widely used in vibration detection applications, pressure detection applications, oscillation applications, piezoelectric device applications, and the like. For example, they can be used in various devices such as piezoelectric filters, piezoelectric vibrators, piezoelectric transformers, piezoelectric ultrasonic transducers, piezoelectric gyro sensors, and knock sensors.

Examples

[0036] The present invention will be further specifically described by way of examples. Table 1 shows the composition ratios of each sample composition. In Table 1, a to d, f correspond to the coefficients included in the following composition formula (1). For d and f, when an element species and a plurality of element species are included, each element species is shown. (K a Na b Li c M1 d ) e (M2 f )O g …(1)

[0037] In Table 1, the sample compositions are indicated using "No.". Sample Nos. 2 to 8, 10, 11 are examples, and Sample No. 1 is a comparative example. Hereinafter, the sample compositions will be described by sample No.

[0038] In the column of d in Table 1, the "composition ratio of each element species" represents the composition ratio in the left column (the column of "element species"). When a plurality of element species are listed in the column of "element species", the order of the values in the column of "composition ratio of each element species" corresponds to the order of the element species in the column of "element species". For example, in Sample No. 1, the "element species" of M1 are barium (Ba) and calcium (Ca), the composition ratio of barium (Ba) is 0.03, and the composition ratio of calcium (Ca) is 0.02.

[0039] In the column of f in Table 1, the "composition ratio of each element species" represents the composition ratio in the left column (the column of "element species"). When multiple element species are listed in the column of "element species", the order of the values in the column of "composition ratio of each element species" corresponds to the order of the element species in the column of "element species". For example, in Sample No. 1, the "element species" of M2 are niobium (Nb), zirconium (Zr), and titanium (Ti), the composition ratio of niobium (Nb) is 0.03, the composition ratio of zirconium (Zr) is 0.02, and the composition ratio of titanium (Ti) is 0.02.

[0040]

Table 1

[0041] 1. Preparation of sample compositions The types and amounts of the raw materials of the first component and the second component were appropriately selected to prepare various sample compositions. The content ratio of Mn (manganese) contained in the sample composition was changed by adjusting the amount of the Mn species during the mixing of the first component, the second component, and the Mn species (the above step T150). The maximum particle diameter of the Mn (manganese) compound contained in the sample composition was changed by adjusting the calcination temperature and calcination time during the calcination of the first component (step T110), the calcination temperature and calcination time during the calcination of the second component (step T130), and the calcination temperature and calcination time during the sintering (step T160) after mixing the first component, the second component, and the Mn species.

[0042] 2. Calculation of the maximum particle diameter of the Mn (manganese) compound The maximum particle diameter of the Mn (manganese) compound contained in the sample composition was measured using an electron probe microanalyzer (EPMA). For the sample composition, Samples 1, 5 to 12 were imaged at a magnification of 1000 times, and Samples 2, 3, and 4 were imaged at 10000 times because their particle sizes were small, and elemental mapping of Mn (manganese) was performed. From the obtained elemental mapping images, the particle diameter of the largest mapped particle was determined as the maximum particle diameter. The particle diameter of the particle was determined by obtaining the minor axis diameter and the major axis diameter (the maximum value on each axis) of the particle and taking the average value of them as the particle diameter.

[0043] 3. Evaluation of Piezoelectric Properties The dielectric loss tanδ of the sample composition was measured using an impedance analyzer. The maximum phase angle θmax of the sample composition was determined by the resonance - anti - resonance method using an impedance analyzer. The piezoelectric constant d of the sample composition 33 was measured using a d 33 meter (ZJ - 4B).

[0044] 4. Evaluation Results The evaluation results are shown in Table 2.

[0045]

Table 2

[0046] (1) Satisfaction Status of Each Requirement for Sample Nos. 1 - 12 Sample Nos. 2 - 8, 10, 11 which are examples satisfy the following requirements (a), (b), and (c). Sample No. 1 which is a comparative example does not contain a secondary phase containing a manganese (Mn) compound and does not satisfy the following requirement (b). Sample No. 1 does not contain a secondary phase containing a manganese (Mn) compound and naturally does not satisfy the following requirement (c). Sample Nos. 9, 12 do not satisfy the following requirement (c). · Requirement (a): It contains a main phase containing a perovskite - type oxide. · Requirement (b): It contains a secondary phase containing a manganese (Mn) compound. · Requirement (c): The maximum particle size of the manganese (Mn) compound is greater than 0 μm and less than 33 μm.

[0047] (2) Results and Discussion The maximum phase angle θmax (an indicator of the ease of poling treatment) of Sample No. 1 was 20°, and the maximum phase angle θmax of Sample Nos. 2 - 12 was in the range of 30° - 81°. Also, the piezoelectric constant d of Sample No. 1 33 (an indicator of piezoelectricity) was 32 pC / N, and the piezoelectric constant d of Sample Nos. 2 - 12 33It was in the range of 41 pC / N to 110 pC / N. As described above, Samples No. 2 to 12 had better piezoelectric properties than Sample No. 1. It is considered that Sample No. 1 satisfied requirements (a) and (b), and as a result, manganese (Mn) oxide was included as a heterogeneous phase inside the sintered body, making polarization easier and improving the piezoelectric properties.

[0048] The dielectric loss tanδ of Samples No. 2 to 8, 10, 11 was in the range of 0.9% to 2.2%, and the dielectric loss tanδ of Samples No. 1, 9, 12 was in the range of 3.3% to 3.9%. As described above, Samples No. 2 to 8, 10, 11 had better piezoelectric properties than Samples No. 1, 9, 12. In Examples, Samples No. 2 to 8, 10, 11 had a maximum particle diameter of manganese (Mn) compound in the range of 0.9 μm to 33 μm and satisfied requirement (c). It is considered that Samples No. 2 to 8, 10, 11 satisfied requirement (c), resulting in an increase in grain boundary resistance and insulation resistance, and thus an improvement in piezoelectric properties.

[0049] 5. Effects of the Examples The lead-free piezoelectric ceramic composition of this example was able to improve the piezoelectric properties.

[0050] This disclosure is not limited to the embodiments detailed above, and various modifications or changes are possible.

Explanation of Reference Signs

[0051] 100... Piezoelectric ceramic 200... Piezoelectric element 301, 302... Electrodes

Claims

【Claim 1】 A main phase containing a perovskite-type oxide, A secondary phase containing a manganese (Mn) compound, and, The maximum particle size of the manganese (Mn) compound is greater than 0 μm and less than 33 μm, The perovskite-type oxide is an alkali-based perovskite-type oxide, The alkali-based perovskite-type oxide has a composition formula (K a Na b Li c M1 d ) e (M2 f )O g (element M1 includes one or more of barium (Ba) or calcium (Ca) among calcium (Ca), strontium (Sr), barium (Ba), element M2 includes at least niobium (Nb) among niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), hafnium (Hf) and two or more kinds including titanium (Ti) or zirconium (Zr), a + b + c + d = 1, a + b + c ≠ 0, 0 ≦ c ≦ 0.04, 0.02 ≦ d ≦ 0.10, 0.80 ≦ e ≦ 1.10 are satisfied, the composition ratio of niobium (Nb) in element M2 is 0.90 or more and 0.98 or less, f = 1, g is an arbitrary value capable of maintaining a perovskite-type crystal structure), and is an oxide represented by The content ratio of manganese (Mn) is greater than 0 mol% and less than or equal to 5 mol%, The manganese (Mn) compound contains a compound represented by the composition formula Mn 3 O 4, a lead-free piezoelectric ceramic composition.

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