JP7696754B2 - Lead-free piezoelectric ceramic composition - Google Patents

Description

This disclosure relates to a lead-free piezoelectric ceramic composition.

Many of the piezoelectric ceramics that have been mass-produced up until now have been made of PZT (lead zirconate titanate) materials and contain lead. However, in recent years, there has been a demand for the development of lead-free piezoelectric ceramics to eliminate the adverse effects of lead on the environment. Such lead-free piezoelectric ceramic materials (referred to as "lead-free piezoelectric ceramic compositions") are 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 different phase to the parent phase that contains alkali niobate-based perovskite-type oxide.

JP 2008-239473 A

However, in the ceramic composition of Patent Document 1, the dielectric loss is relatively large despite the addition of manganese oxide to the ceramic sintered body, so the maximum phase angle is small and the polarization is insufficient. Therefore, such a ceramic composition does not provide sufficient piezoelectric properties. Therefore, there is a demand for further improvement in the piezoelectric properties of ceramic compositions.
The present disclosure has been made in view of the above-mentioned circumstances, and has an object to improve piezoelectric characteristics. The present disclosure can be realized in the following forms.

[1] A main phase including a perovskite-type oxide;
a subphase including a manganese (Mn) compound;
Including,
The lead-free piezoelectric ceramic composition, wherein the maximum particle size of the manganese (Mn) compound is greater than 0 μm and less than 33 μm.

[2] The lead-free piezoelectric ceramic composition according to [1], wherein the perovskite oxide is an alkaline perovskite oxide.

[3] The lead-free piezoelectric ceramic composition according to [2], wherein the alkaline perovskite oxide contains niobium (Nb).

[4] The lead-free piezoelectric ceramic composition according to [2] or [3], wherein the alkali perovskite oxide is an oxide represented by a composition formula (K _a Na _b Li _c M1 _d ) _e (M2 _f ) O _g (wherein M1 is one or more of calcium (Ca), strontium (Sr) and barium (Ba), M2 is one or more of niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr) and hafnium (Hf) including at least niobium (Nb) or tantalum (Ta), a + b + c + d = 1, a + b + c ≠ 0, 0.80 ≦ e ≦ 1.10, f = 1, and g are any values that can maintain a perovskite crystal structure).

[5] A lead-free piezoelectric ceramic composition according to any one of [1] to [4], in which the manganese (Mn) content is greater than 0 mol% and less than or equal to 5 mol%.

[6] The lead-free piezoelectric ceramic composition according to any one of [1] to [5], wherein the manganese (Mn) compound includes a compound represented by the composition formula Mn ₃ O ₄ .

The lead-free piezoelectric ceramic composition disclosed herein can improve piezoelectric properties.

1 is a flowchart illustrating a method for manufacturing a piezoelectric element according to an embodiment of the present disclosure. 1 is a perspective view illustrating a piezoelectric element according to an embodiment of the present disclosure.

The present disclosure is described in detail below. In this specification, when a numerical range is described using "to" it is intended to include the lower limit and the upper limit unless otherwise specified. For example, the description "10 to 20" is intended to include both the lower limit "10" and the upper limit "20". In other words, "10 to 20" has the same meaning as "10 or more and 20 or less".

1. Lead-free piezoelectric ceramic composition The lead-free piezoelectric ceramic composition of the present embodiment does not contain Pb (lead), and contains a main phase containing a perovskite-type oxide, and a subphase containing a manganese (Mn) compound.

(1) The main phase perovskite oxide is preferably an alkali perovskite oxide containing an alkali metal, and more preferably an alkali perovskite oxide containing Nb (niobium).

A preferred example of the perovskite oxide is one represented by the following composition formula (Formula (1)). The element M1 is one or more of calcium (Ca), strontium (Sr), and barium (Ba). The element M2 is one or more of niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf), including at least niobium (Nb) or tantalum (Ta). For example, the element M2 is one or more of niobium (Nb), titanium (Ti), zirconium (Zr), and hafnium (Hf). For example, the element M2 is one or more of tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf). For example, element M2 is one or more of niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf). The value of g is any value that can maintain the perovskite crystal structure. That is, the amount of O atoms is set to be an amount that can maintain the perovskite crystal structure.

(K _a Na _b Li _c M1 _d ) _e (M2 _f ) O _g …(1)

In the above composition formula (1), the proportions of the respective elements are preferably in the following ranges from the viewpoint of the electrical properties or piezoelectric properties (particularly the 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 crystal structure. a+b+c+d=1
a+b+c≠0

In the above composition formula (1), the ratio of each element is more preferably within 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 is any value that can maintain the perovskite crystal structure. a+b+c+d=1
a+b+c≠0

In the above composition formula (1), the ratio of each element is more preferably within the following range.
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 is any value that can maintain the perovskite crystal structure. a+b+c+d=1
a+b+c≠0

In the above composition formula (1), when M1 is barium (Ba) and calcium (Ca), composition formula (1) is expressed 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 element ratio X1 of barium (Ba) is preferably in the range of 0.02≦X1≦0.05. The element ratio Y1 of calcium (Ca) is preferably in the range of 0.01≦X1≦0.05.

In the above composition formula (1), when M1 is calcium (Ca), composition formula (1) is expressed as the following composition formula (3): d=Y1.

(K _a Na _b Li _c Ca _Y1 ) _e (M2 _f ) O _g …(3)

The element ratio Y1 of calcium (Ca) is preferably in the range of 0.01≦X1≦0.03.

In the above composition formula (1), when M1 is barium (Ba) and strontium (Sr), the composition formula (1) is expressed 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 element ratio X1 of barium (Ba) is preferably in the range of 0.04≦X1≦0.06. The element ratio Z1 of strontium (Sr) is preferably in the range of 0.04≦Z1≦0.06.

In the above composition formula (1), when M2 is niobium (Nb), zirconium (Zr), and titanium (Ti), the composition formula (1) is expressed 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 element ratio X2 of niobium (Nb) is preferably in the range of 0.80≦X2≦1.0. The element ratio Y2 of zirconium (Zr) is preferably in the range of 0.02≦X1≦0.06. The element ratio Z2 of titanium (Ti) is preferably in the range of 0.02≦X1≦0.06.

In the above composition formula (1), when M2 is niobium (Nb) and titanium (Ti), the composition formula (1) is expressed as the following composition formula (6): f = X2 + Z2.

(K _a Na _b Li _c M1 _d ) _e (Nb _X2 Ti _Z2 ) O _g …(6)

The element ratio X2 of niobium (Nb) is preferably in the range of 0.90≦X2≦1.0, and the element ratio Z2 of titanium (Ti) is preferably in the range of 0.01≦X1≦0.03.

In the above composition formula (1), when M2 is niobium (Nb) and zirconium (Zr), the composition formula (1) is expressed as the following composition formula (7): f = X2 + Y2.

(K _a Na _b Li _c M1 _d ) _e (Nb _X2 Zr _Y2 ) O _g …(7)

The element ratio X2 of niobium (Nb) is preferably in the range of 0.90≦X2≦1.0, and the element ratio Y2 of zirconium (Zr) is preferably in the range of 0.02≦X1≦0.04.

(2) Subphase The lead-free piezoelectric ceramic composition of the present embodiment includes a subphase containing a manganese (Mn) compound. More preferably, the subphase may include a metal oxide. The manganese (Mn) compound preferably includes a compound represented by the composition formula _Mn3O4 . The manganese (Mn) compound may include a compound represented by the composition formula MnO, _MnO2 , _Mn2O3 , _MnCO3 , or _{the like} , and may include other metal elements such as Ti.

The maximum particle size of the manganese (Mn) compound is preferably greater than 0 μm and less than 33 μm. The maximum particle size of the manganese (Mn) compound is more preferably greater than 0.2 μm and less than 11 μm. The maximum particle size of the manganese (Mn) compound is even more preferably greater than 0.5 μm and less than 5 μm.

The manganese (Mn) content in the lead-free piezoelectric ceramic composition is preferably greater than 0 mol% and less than 5 mol%. The manganese (Mn) content in the lead-free piezoelectric ceramic composition is more preferably greater than 0.3 mol% and less than 4 mol%. The manganese (Mn) content in the lead-free piezoelectric ceramic composition is even more preferably greater than 0.6 mol% and less than 2.5 mol%.

Figure 1 is an example of a flow chart showing a method for manufacturing a piezoelectric element in one embodiment of the present disclosure. A first component and a second component prepared as follows are mixed to form a main phase and a subphase. The first component is the main component contained in the main phase. The second component is a component different from the main phase.

In step T110, the raw material of the first component is mixed. The first component is the main component contained in the main phase. In step T110, the raw material of the first component is selected from K ₂ CO ₃ powder, Na ₂ CO ₃ powder, Li ₂ CO ₃ powder, CaCO ₃ powder, SrCO ₃ powder, BaCO ₃ powder, Nb ₂ O ₅ powder, Ta ₂ O ₅ powder, TiO ₂ powder, ZrO ₂ powder, MgO powder, Fe ₂ O ₃ powder, CoO powder, ZnO powder, etc., and weighed according to the values of the coefficients (for example, a to f, i in the composition formula (8) of the first component below) in the composition formula (8) of the first component described below. The values of element ratios b, c, d, and e are adopted as the values of element ratios b, c, d, and e in the composition formula (1) above.

(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 in a ball mill to obtain a slurry. The wet-mixing using a ball mill is preferably performed for 15 hours or more. In step T120, the mixed powder obtained by drying the slurry is calcined, for example, in an air atmosphere at 600° C. to 1100° C. for 1 hour to 10 hours to generate a calcined powder of the first component.

In step T130, the raw material mixing of the second component is performed. The composition of the second component is preferably K _0.85 Ti _0.85 Nb _1.15 O _5. The composition of the second component may be KTiNbO ₅ , K _0.90 Ti _0.90 Nb _1.10 O ₅ , etc. As the raw material of the second component, K ₂ CO ₃ powder, Nb ₂ O ₅ powder, and TiO ₂ 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 in a ball mill to obtain a slurry. The wet mixing using a ball mill is preferably performed for 15 hours or more. In step T140, the mixed powder obtained by drying the slurry is calcined, for example, in an air atmosphere at 600°C to 1100°C for 1 hour to 10 hours to generate a calcined powder of the second component.

In step T150, the first component, the second component, and Mn species (e.g., MnCO ₃ , MnO, Mn ₂ O ₃ , MnO ₂ , etc.) are weighed, and a dispersant, a binder, and ethanol are added, followed by grinding and mixing in a ball mill to obtain a slurry. This slurry may be calcined again, and then ground and mixed. The slurry is then dried, granulated, and uniaxially pressed, for example, at a pressure of 20 MPa, to form it into a desired shape. As an embodiment of the present disclosure, a typical shape of the piezoelectric ceramic suitable for the composition is, for example, a disk shape or a cylindrical shape. Then, for example, a CIP process (cold isostatic pressing process) is performed at a pressure of 150 MPa to obtain a molded body. In step T160, the obtained molded body (CIP pressed body) is fired, for example, at 900°C to 1300°C in an air atmosphere for 1 to 10 hours, to obtain a piezoelectric ceramic. The firing in step T160 may be performed in an O ₂ atmosphere. Next, in step T170, the piezoelectric ceramic is processed according to the dimensional accuracy required for the piezoelectric element. In step T180, electrodes are attached to the piezoelectric ceramic thus obtained, and in step T190, a polarization process is performed.

The above-mentioned manufacturing method is one example, and various other steps and processing conditions for manufacturing piezoelectric elements can be used. For example, as shown in FIG. 1, the first component and the second component are produced separately in advance, and then the powders of the two are mixed and fired. Alternatively, the piezoelectric ceramic composition may be manufactured by mixing raw materials containing the first component and the second component together and firing them. However, according to the manufacturing method of FIG. 1, it is easier to more strictly control the composition of the first component and the second component, so it is possible to increase the yield of the piezoelectric ceramic composition.

2 is a perspective view showing a piezoelectric element according to an embodiment of the present disclosure. The piezoelectric element 200 has electrodes 301, 302 attached to the upper and lower surfaces of a disk-shaped piezoelectric ceramic 100. Note that piezoelectric elements of various other shapes and configurations can be formed.

3. Use of lead-free piezoelectric ceramic composition and piezoelectric element The lead-free piezoelectric ceramic composition and piezoelectric element according to the embodiment of the present disclosure can be widely used for vibration detection, pressure detection, oscillation, piezoelectric device, etc. 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.

The present invention will be explained more specifically with reference to examples.
The composition ratios of each sample composition are shown in Table 1. In Table 1, a to d and f correspond to coefficients included in the following composition formula (1). Note that d and f indicate the element type, and when multiple element types are included, each element type is indicated.

(K _a Na _b Li _c M1 _d ) _e (M2 _f ) O _g …(1)

In Table 1, the sample compositions are indicated using a "No." Samples No. 2 to 8, 10, and 11 are examples, and Sample No. 1 is a comparative example. Hereafter, the sample compositions will be explained by sample number.

The "Composition ratio of each elemental species" in column d of Table 1 represents the composition ratio in the left column (the "elemental species" column). When multiple elemental species are listed in the "elemental species" column, the order of the values in the "Composition ratio of each elemental species" column corresponds to the order of the elemental species in the "elemental species" column. For example, in sample No. 1, the "elemental 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.

The "Composition ratio of each element type" in column f of Table 1 represents the composition ratio in the left column (the "element type" column). When multiple element types are listed in the "element type" column, the order of the values in the "Composition ratio of each element type" column corresponds to the order of the element types in the "element type" column. For example, in sample No. 1, the "element types" of M2 are niobium (Nb), zirconium (Zr), and titanium (Ti), with the composition ratio of niobium (Nb) being 0.03, the composition ratio of zirconium (Zr) being 0.02, and the composition ratio of titanium (Ti) being 0.02.

1. Preparation of sample compositions Various sample compositions were prepared by appropriately selecting the type and amount of the raw material of the first component and the raw material of the second component. The content ratio of Mn (manganese) contained in the sample composition was changed by adjusting the amount of Mn species when mixing the first component, the second component, and the Mn species (step T150 above). The maximum particle size of the Mn (manganese) compound contained in the sample composition was changed by adjusting the calcination temperature and calcination time when calcining the first component (step T110), the calcination temperature and calcination time when calcining the second component (step T130), and the calcination temperature and calcination time when sintering the first component, the second component, and the Mn species after mixing (step T160).

2. Calculation of maximum particle size of Mn (manganese) compound The maximum particle size of Mn (manganese) compound contained in the sample composition was measured using an electron probe microanalyzer (EPMA). Samples 1, 5 to 12 were photographed at a magnification of 1000 times, and samples 2, 3, and 4 were photographed at a magnification of 10,000 times because the particle size was small, and elemental mapping of Mn (manganese) was performed. From the obtained elemental mapping image, the particle size of the largest particle mapped was calculated and defined as the maximum particle size. The particle size of the particle was determined by calculating the minor axis diameter and major axis diameter (maximum value on each axis) of the particle, and the average value of these was defined as the particle size.

3. Evaluation of Piezoelectric Properties The dielectric loss tan δ of the sample composition was measured using an impedance analyzer. The maximum phase angle θmax of the sample composition was determined by the resonance-antiresonance method using an impedance analyzer. The piezoelectric constant _d33 of the sample composition was measured using a _d33 meter (ZJ-4B).

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

(1) Satisfaction of each requirement of Samples No. 1 to 12 Samples No. 2 to 8, 10, and 11, which are examples, satisfy the following requirements (a), (b), and (c). Sample No. 1, which is a comparative example, does not contain a subphase containing a manganese (Mn) compound and does not satisfy the following requirement (b). Sample No. 1 does not contain a subphase containing a manganese (Mn) compound and does not naturally satisfy the following requirement (c). Samples No. 9 and 12 do not satisfy the following requirement (c).
Requirement (a): The main phase contains a perovskite-type oxide.
Requirement (b): The alloy contains a subphase 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.

(2) Results and Discussion The maximum phase angle θmax (index of ease of polarization processing) of Sample No. 1 was 20°, and the maximum phase angle θmax of Samples No. 2 to 12 was in the range of 30° to 81°. In addition, the piezoelectric constant d ₃₃ (index of piezoelectricity) of Sample No. 1 was 32 pC/N, and the piezoelectric constant d ₃₃ of Samples No. 2 to 12 was in the range of 41 pC/N to 110 pC/N. As described above, Samples No. 2 to 12 had better piezoelectric characteristics than Sample No. 1. It is considered that Sample No. 1 satisfied the requirements (a) and (b), and thus manganese (Mn) oxide was contained inside the sintered body as a different phase, which facilitated polarization and improved the piezoelectric characteristics.

The dielectric loss tan δ of samples No. 2 to 8, 10, and 11 was in the range of 0.9% to 2.2%, and the dielectric loss tan δ of samples No. 1, 9, and 12 was in the range of 3.3% to 3.9%. As described above, samples No. 2 to 8, 10, and 11 had better piezoelectric properties than samples No. 1, 9, and 12. Samples No. 2 to 8, 10, and 11, which are examples, have a maximum particle size of manganese (Mn) compounds in the range of 0.9 μm to 33 μm, and satisfy requirement (c). It is believed that samples No. 2 to 8, 10, and 11 satisfy requirement (c), which increases the grain boundary resistance and increases the insulation resistance, resulting in improved piezoelectric properties.

5. Effects of the Example The lead-free piezoelectric ceramic composition of the example was able to improve the piezoelectric characteristics.

This disclosure is not limited to the embodiments detailed above, and various modifications and variations are possible.

100... Piezoelectric ceramic 200... Piezoelectric element 301, 302... Electrode

Claims (1)

a main phase including a perovskite-type oxide;
a subphase including a manganese (Mn) compound;
Including,
The maximum particle size of the manganese (Mn) compound is greater than 0 μm and less than 33 μm;
the perovskite oxide is an alkaline perovskite oxide,
The alkali perovskite oxide has a composition formula (K _a Na _b Li _c M1 _d ) _e (M2 _f ) O _g (element M1 is one or more elements selected from calcium (Ca), strontium (Sr), and barium (Ba) including barium (Ba) or calcium (Ca); element M2 is two or more elements selected from niobium (Nb), tantalum (Ta), titanium (Ti), zirconium (Zr), and hafnium (Hf) including at least niobium (Nb) and titanium (Ti) or zirconium (Zr); a+b+c+d=1, a+b+c≠0, 0≦c≦0.04, 0.02≦d≦0.10, and 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, and g are any values that can maintain a perovskite crystal structure),
The manganese (Mn) content is greater than 0 mol% and less than 5 mol%,
The lead-free piezoelectric ceramic composition, wherein the manganese (Mn) compound includes a compound represented by _the composition formula _Mn3O4 .

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