JP2014034507A - Piezoelectric ceramic and piezoelectric actuator using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic and a piezoelectric actuator having great specific permittivities and d constants and capable of mitigating depolarizations arising in accordance with drives thereof.SOLUTION: The provided piezoelectric ceramic has a PZT-type perovskite structure, includes, as compositional elements, Pb, Sr, Mg, Nb, Zr, and Ti, has a specific permittivity of 3000 or above and a piezoelectric strain constant dof 200 or above, and yields, in a case where the impressed voltage retention time at room temperature is assumed to be 1 sec, an insulation resistance-minimizing impression reverse voltage of 670 V/mm or above. It accordingly becomes possible to mitigate depolarization arising in accordance with the impression of a reverse voltage against the polarizing direction while the specific permittivity and d constant are increased.

Description

  The present invention relates to a piezoelectric ceramic having a PZT perovskite structure and a piezoelectric actuator having a bimorph structure using the same.

  Conventionally, piezoelectric ceramics having a perovskite structure mainly composed of so-called PZT (lead zirconate titanate) have been used as piezoelectric actuator materials because of their high piezoelectric characteristics.

For example, in Patent Document 1, a part of Pb atoms in xPb (Mg _1/3 Nb _2/3 ) O ₃ —yPbTiO ₃ —zPbZrO ₃ based ceramic composition was selected from the Sr, Ba, and Ca groups. Ferroelectricity substituted with at least one atom up to 20 atomic percent, x = 87.5-1, y = 81.3-0, z = 95.0-0, x + y + z = 100 (both mole percent) A characteristic porcelain composition is disclosed. With such a composition, the electromechanical coupling coefficient and dielectric constant are increased, and the resonance resistance is decreased.

Patent Document 2 discloses that in an oxide composition represented by (Pb _1-ab M _a ) (Mg _1/3 Nb _2/3 ) _x Ti _y Zr _z O ₃ , b = 0.005 to 0 .05, and M is at least one atom of Sr, Ba, and Ca, a = 0.01 to 0.1, x = 0.10 to 0.50, y = 0.30. A lead zirconate titanate-based oxide composition in which 0.50, z = 0.10 to 0.50, and x + y + z = 1 (all in atomic ratio) is disclosed. With such a composition, the relative dielectric constant and the electromechanical coupling coefficient are increased.

Patent Document _3, in _{(Pb 1-x Sr x)} (Zr y Ti 1-y M z) O 3 + z ' [wherein, M represents one or more elements selected from Nb, Sr, Ta, or La 0.08 ≦ x ≦ 0.14, 0.49 ≦ y−0.5x ≦ 0.51, 0.005 ≦ z ≦ 0.02, z ′ is 3 / 2z for La, M is Sb, Ta or In the case of Nb, M _z O _{z ′} is a value that makes the stoichiometric compound like 5 / 2z. A piezoelectric ceramic composition having a composition represented by the following formula is disclosed. This makes it possible to provide a material that has a large piezoelectric strain constant, a high Curie temperature, and is particularly suitable for use in automobiles and the like.

In Patent Document 4, it is represented by the composition of the composition formula Pb _z [(Ti _x Zr _1-x ) _1-y M _y ] O ₃ (where M is at least one of Nb, Sb, and W). A piezoelectric ceramic composition for laminated piezoelectric elements is disclosed. X and y in the composition formula are 0.45 ≦ x ≦ 0.52 and 0.005 ≦ y ≦ 0.03, and z in the composition formula is 0.95 ≦ z ≦ 0.998. Thus, Pb is reduced from the stoichiometric composition. This makes it possible to provide an actuator with excellent displacement performance and heat resistance and low power consumption.

Japanese Examined Patent Publication No. 44-17103 Japanese Patent Publication No. 4-78582 Japanese Patent Publication No.7-110786 Japanese Patent No. 4752156

  When the materials described in Patent Documents 1 and 2 are used for the piezoelectric actuator, the relative permittivity is large and the d constant is large, so that a sufficient drive displacement can be obtained. However, when the piezoelectric element is driven, a voltage is continuously applied to the piezoelectric body in the direction opposite to the polarization direction. Therefore, depolarization occurs with the drive, and the drive displacement decreases. On the other hand, when the materials described in Patent Documents 3 and 4 are used, it is considered that depolarization can be reduced because they have characteristics such as a high Curie temperature. Inferior.

  The present invention has been made in view of such circumstances, and provides a piezoelectric ceramic having a large relative permittivity and a d constant and capable of reducing depolarization that occurs during driving, and a piezoelectric actuator using the piezoelectric ceramic. For the purpose.

(1) In order to achieve the above object, the piezoelectric ceramic of the present invention is a piezoelectric ceramic having a PZT-based perovskite structure, containing Pb, Sr, Mg, Nb, Zr, and Ti as constituent elements, and having a relative dielectric constant. Is 3000 or more, the piezoelectric strain constant d ₃₁ is 200 or more, and the applied reverse voltage that minimizes the insulation resistance is 670 V / mm or more when the voltage application holding time is 1 second at room temperature. It is said.

  As described above, the piezoelectric ceramic of the present invention can reduce depolarization caused by application of a reverse voltage with respect to the polarization direction while increasing the relative dielectric constant and the d constant. As a result, the drive performance of the piezoelectric actuator can be improved.

  (2) Moreover, the piezoelectric ceramic of the present invention is characterized in that the X-ray diffraction peak position by the (101) plane is in the range of 2θ = 31.2 to 31.5 degrees. By having such a structure, high piezoelectric characteristics can be maintained.

  (3) The piezoelectric actuator of the present invention is a piezoelectric actuator having a bimorph structure, which is formed of a metal-made shim plate and elastic main surfaces of both the shim plate and the piezoelectric ceramic. And a piezoelectric element. Accordingly, it is possible to realize a piezoelectric actuator that has high driving performance and reduces depolarization that occurs with driving.

  According to the present invention, it is possible to realize a piezoelectric ceramic that has a large relative dielectric constant and a d constant and reduces depolarization that occurs with driving.

(A)-(d) is a graph which shows the measurement result of the piezoelectric property of the sample produced on each condition. It is a circuit diagram which shows the structure of experiment. It is a graph which shows the insulation resistance at the time of the reverse voltage application by each applied voltage in room temperature (25 degreeC). It is a graph which shows the applied reverse voltage from which the insulation resistance in each temperature becomes the minimum. It is a graph which shows the diffraction X-ray peak of each sample in 31 degree vicinity.

  Next, embodiments of the present invention will be described with reference to the drawings.

(Configuration of piezoelectric ceramics)
The piezoelectric ceramic of the present invention has a PZT perovskite structure, has high piezoelectric characteristics, and can reduce depolarization that occurs with driving. In particular, it is suitable for application to a piezoelectric element of a bimorph type piezoelectric actuator.

This piezoelectric ceramic is configured to contain Pb, Sr, Mg, Nb, Zr, and Ti as composition elements. When the relative dielectric constant is 3000 or more, the piezoelectric strain constant d ₃₁ is 200 or more, and the applied voltage is 670 V / mm or more at which the insulation resistance is minimized when the voltage application holding time is 1 second at room temperature. It is. In this way, depolarization caused by application of a reverse voltage with respect to the polarization direction can be reduced while maintaining a large relative dielectric constant and d constant.

  Since the relative dielectric constant and the d constant are thus large, the driving performance of the piezoelectric actuator can be improved. The reason why such characteristics can be realized is that the crystal grains constituting the piezoelectric ceramic have a crystal structure with high piezoelectric characteristics. Each crystal particle has a perovskite-type tetragonal crystal structure, and an X-ray diffraction peak position by the (101) plane is generated in a range of 2θ = 31.2 to 31.5 degrees. The crystal grain structure is uniform throughout the piezoelectric ceramic. The electromechanical coupling coefficient kr is 60% or more.

  The applied reverse voltage at which the insulation resistance is minimized when the voltage application holding time is 1 second at room temperature is 670 V / mm or more. When such a piezoelectric ceramic is used for a bimorph piezoelectric actuator, the depolarization speed can be reduced while maintaining a sufficient driving displacement. The applied reverse voltage that minimizes the insulation resistance when the voltage application holding time is 1 second is more preferably 700 V / mm or more.

(Method for manufacturing piezoelectric ceramics and piezoelectric actuator)
First, an oxide satisfying (1) of the following conditions in which the compounding ratio of the constituent elements is used as the first material, and an oxide satisfying (2) in the following conditions of the constituent elements is the second material: Then, each material containing Pb, Sr, etc. is weighed and mixed so as to be the first material, and calcined to produce a piezoelectric ceramic powder having the first material. Similarly, a piezoelectric ceramic powder having the second material is generated.

(1) Pb _a Sr _b (Mg _1/3 Nb _2/3 ) _c Zr _d Ti _e O ₃
0.92 ≦ a ≦ 0.94, 0.04 ≦ b ≦ 0.06, 0.36 ≦ c ≦ 0.39, 0.24 ≦ d ≦ 0.27, 0.36 ≦ e ≦ 0.38, c + d + e = 1
_{(2) Pb f Sr g Nb} h Zr j Ti k O 3
0.95 ≦ f ≦ 0.98, 0.04 ≦ g ≦ 0.06, 0.15 ≦ h ≦ 0.25, 0.52 ≦ j ≦ 0.55, 0.45 ≦ k ≦ 0.48, h + j + k = 1

  These raw material powders are mixed at a predetermined ratio of 1st material: 2nd material = 6: 4 to 8: 2. At that time, for example, mil mixing is performed with balls such as zirconia balls. Then, the granulated product is press-molded to produce a molded body. In addition, you may prepare the raw material powder of a composition of a predetermined | prescribed mixing ratio previously, and may produce a molded object.

  Next, the formed body is fired at 1150 ° C. or more and 1200 ° C. or less, and the obtained piezoelectric ceramic sintered body is processed and polished to form a predetermined electrode. A piezoelectric element in which a piezoelectric body is formed with the piezoelectric ceramic of the present invention can be obtained by subjecting the sintered body on which the electrode is formed to a polarization treatment. The firing temperature is preferably around 1200 ° C.

  When producing a molded body, a green sheet is produced from a slurry obtained by mixing raw material powders, a predetermined electrode is printed and laminated, and a molded body for a laminated piezoelectric element is obtained. May be. A piezoelectric actuator having a bimorph structure can be manufactured by bonding the piezoelectric element, which is baked and baked with electrodes, to both main surfaces of a metal shim plate having elasticity.

(Experiment 1: Piezoelectric characteristics)
Next, experiments conducted on the piezoelectric ceramic of the present invention will be described. First, the first material and the second material are mixed at a predetermined mixing ratio, and fired at 1200 ° C. or 1150 ° C. to produce a piezoelectric ceramic sintered pellet sample. density of to the sample, the dielectric constant, _kr, was measured _{d 31.}

Samples were prepared with mixing ratios of first material: second material = 10: 0, 9: 1, 8: 2, 7: 3, and 6: 4, respectively. Measurements of density, JIS R1634, the dielectric constant, measurement of kr and _{d 31} was carried out based on ,, JEITA EM-450.

FIGS. 1A to 1D are graphs showing the measurement results of the piezoelectric characteristics of a sample manufactured under each condition. Table 1 below shows the measurement results in a table.

Such experimental results, and it has become baked densification towards the sample at 1200 ° C., the dielectric constant, kr, superior results for d ₃₁ was obtained. Also, the fired sample at 1200 ° C., 6: be of mixing ratio of 4, relative dielectric constant of 3000 or more, kr is 60% or _{more, d 31} is 220 × ^{10 -12} m / V or more, sufficient It was confirmed that the piezoelectric properties were excellent. On the other hand, it was found that the sample having a mixing ratio of 9: 1 did not differ greatly in piezoelectric properties from that formed at 8: 2.

(Experiment 2: Depolarization speed)
Considering the above experimental results, experiments on the depolarization rate were performed on four samples with a firing temperature of 1200 ° C. and mixing ratios of 10: 0, 8: 2, 7: 3, and 6: 4. A polarized piezoelectric ceramic sample having the above conditions was prepared, a predetermined reverse voltage was applied for 1 second, and the insulation resistance was measured. Thus, the applied reverse voltage when the insulation resistance was minimized was measured. The higher the so-called “reversal voltage” measured in this way, the slower the “depolarization speed” of the piezoelectric ceramic.

  FIG. 2 is a circuit diagram showing the configuration of the experiment. As shown in FIG. 2, the insulation resistance was measured by measuring the resistance when the piezoelectric ceramic sample 10 was assumed to be a parallel circuit of a resistor 11 and a capacitor 12.

  FIG. 3 is a graph showing the insulation resistance when a reverse voltage is applied by each applied voltage at room temperature (25 ° C.). As shown in FIG. 3, as the mixing ratio approaches 10: 0 to 6: 4, the applied reverse voltage that minimizes the insulation resistance increases.

Such measurement was also performed at 40 ° C., 60 ° C., and 80 ° C. under different temperature conditions. FIG. 4 is a graph showing the applied reverse voltage at which the insulation resistance at each temperature is minimized. Table 2 shown below shows the measurement results in a table.

  According to FIG. 4, when the mixing ratio of the first material and the second material is represented by x: (10−x), the applied reverse voltage is remarkably increased with the composition satisfying x ≦ 8 as a boundary. I understand that. Such a tendency was the same at each temperature of room temperature to 80 ° C.

(Experiment 3: X-ray diffraction angle)
X-ray diffraction peaks were measured for four samples with mixing ratios of 10: 0, 8: 2, 7: 3, and 6: 4 and piezoelectric ceramic samples (mixing ratio of 0:10) formed with only the second material. did. All samples used were fired at 1200 ° C.

  First, a sample was set in a standard sample holder and placed on a MultiFlex goniometer. Then, CuKα X-rays adjusted with a fixed monochromator were incident on the sample, and the X-ray intensity and diffraction angle were measured. The diffraction angle was measured continuously from 3 ° to 90 °.

  FIG. 5 is a graph showing the diffraction X-ray peak of each sample near 31 °. Since the strongest peak was observed in the vicinity of 31 °, this is representatively shown in FIG. As shown in FIG. 5, only the diffraction peak generated in the sample having a mixing ratio of 0:10 exists in the vicinity of 30.9 °, which is different from the diffraction peak positions of other samples. On the other hand, the diffraction peaks generated in the samples having the mixing ratios of 10: 0, 8: 2, 7: 3, and 6: 4 are present in the vicinity of 31.3 to 31.4, and the mixing ratio is 8: 2 to 6: 4. It was confirmed that the structure of the crystal particles composing the sample of this sample is equivalent to the crystal structure of the piezoelectric ceramics when produced with only the first material.

10 Piezoelectric ceramic sample 11 Resistance 12 Capacitor

Claims (3)

Piezoelectric ceramics having a PZT perovskite structure,
The composition elements include Pb, Sr, Mg, Nb, Zr, Ti,
The relative dielectric constant is 3000 or more, the piezoelectric strain constant d ₃₁ is 200 or more,
A piezoelectric ceramic, wherein an applied reverse voltage at which an insulation resistance is minimized is 670 V / mm or more when a voltage application holding time is 1 second at room temperature.   2. The piezoelectric ceramic according to claim 1, wherein an X-ray diffraction peak position by the (101) plane is in a range of 2θ = 31.2 to 31.5 degrees. A piezoelectric actuator having a bimorph structure,
A shim plate made of metal and having elasticity;
A piezoelectric actuator comprising: a piezoelectric element provided on both principal surfaces of the shim plate and formed of the piezoelectric ceramic according to claim 1.

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