JP6321562B2 - Piezoelectric ceramic composition, piezoelectric element, and piezoelectric vibration device - Google Patents

Description

  The present invention relates to a piezoelectric ceramic composition, a piezoelectric element using the same, and a piezoelectric vibration device.

  Conventionally, a piezoelectric ceramic composition mainly composed of lead zirconate titanate (PZT) is known, and since this PZT piezoelectric ceramic composition is excellent in heat resistance and aging, for example, a resonator, a vibrator, It is used for an actuator, an acoustic component, etc. (for example, refer patent document 1).

Japanese Patent Application Laid-Open No. 05-017218

  The piezoelectric ceramic composition of Patent Document 1 has a high electromechanical coupling coefficient and heat resistance, and a low temperature coefficient of resonance frequency. Specifically, the electromechanical coupling coefficient kp is 60.4% to 62.0%, the heat resistance temperature is 300 ° C. to 310 ° C., and the temperature coefficient of the resonance frequency is about 20 ppm / ° C. to 30 ppm / ° C.

  However, since the dielectric constant εr of the piezoelectric ceramic composition of Patent Document 1 is 1090 to 1190, the piezoelectric constant d31 is estimated to be 120 pm / V to 140 pm / V, and the mechanical quality factor Qm is 100 to 140. . When a piezoelectric element having a piezoelectric layer formed of such a piezoelectric ceramic composition is used in a piezoelectric vibration device such as an acoustic generator, the sound pressure is low because the piezoelectric constant d31 is small, and the mechanical quality factor is low. Since Qm is high, the difference between the peak and the dip is large in the frequency-sound pressure characteristics, and the sound quality may be deteriorated.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a piezoelectric ceramic composition, a piezoelectric element, and a piezoelectric vibration device having a large piezoelectric d constant and a low mechanical quality factor Qm.

The piezoelectric ceramic composition of the present invention has the general formula:
_{Pb a (Yb 2/3 W 1/3)} x (Zn 1/2 W 1/2) y (Ti z Zr 1-z) 1-x-y O 3
Where a, x, y, z are
0.97 ≦ a ≦ 1.03
0.005 ≦ x ≦ 0.08
0.03 ≦ y ≦ 0.15
0.45 ≦ z ≦ 0.55
It contains the compound perovskite type compound which satisfies these.

  The piezoelectric element of the present invention is characterized in that a piezoelectric layer made of the above-described piezoelectric ceramic composition and an internal electrode layer are laminated.

  According to another aspect of the present invention, there is provided a piezoelectric vibration device comprising: the above-described piezoelectric element; and a vibration plate to which the piezoelectric element is attached and vibrates by vibration of the piezoelectric element.

  According to the present invention, a piezoelectric ceramic composition having a large piezoelectric d constant and a low mechanical quality factor Qm can be realized.

(A) is a schematic perspective view which shows an example of the piezoelectric element of this embodiment, (b) is a schematic sectional drawing cut | disconnected by the AA line shown to (a). It is a schematic perspective view which shows an example of the piezoelectric vibration apparatus of this embodiment.

  Hereinafter, an example of the piezoelectric ceramic composition of the present embodiment will be described.

The piezoelectric ceramic composition of the present embodiment has a general formula of Pb _a (Yb _2/3 W _1/3 ) _x (Zn _1/2 W _1/2 ) _y (Ti _z Zr _1-z ) _{1-x- y} O ₃ , a, x, y, z are 0.97 ≦ a ≦ 1.03, 0.005 ≦ x ≦ 0.08, 0.03 ≦ y ≦ 0.15, 0.45 ≦ A composite perovskite compound satisfying z ≦ 0.55 is included.

The composite perovskite type compound in the piezoelectric ceramic composition of the present embodiment is a lead zirconate titanate-based material containing at least Pb, Yb, W, Zn, Ti, and Zr as metal elements. The general formula is Pb _a ( _{Yb 2/3 W 1/3) x (Zn} 1/2 W 1/2) y (Ti z Zr 1-z) can be represented by _{1-x-y O 3.}

Here, except when substituted partially described later, in the Pb _a a A site of the complex perovskite compound, a piezoelectric constant d31 is decreased outside the range of 0.97 ≦ a ≦ 1.03, There is a tendency that a sufficient amount of displacement cannot be obtained as a piezoelectric ceramic composition. When such a piezoelectric ceramic composition is used as, for example, an acoustic generator as a piezoelectric vibration device, it is expected that the sound pressure is low. Therefore, it is necessary to satisfy 0.97 ≦ a ≦ 1.03.

On the other hand, in (Yb _2/3 W _1/3 ) _x (Zn _1/2 W _1/2 ) _y (Ti _z Zr _1-z ) _1-xy , which is the B site of this composite perovskite compound, x Is outside the range of 0.005 ≦ x ≦ 0.08, the piezoelectric constant d31 tends to decrease, and a sufficient amount of displacement as a piezoelectric ceramic composition tends not to be obtained. Further, even when y is outside the range of 0.03 ≦ y ≦ 0.15, the piezoelectric constant d31 tends to decrease, and a sufficient amount of displacement as a piezoelectric ceramic composition tends not to be obtained. Further, even when z is outside the range of 0.45 ≦ z ≦ 0.55, the piezoelectric constant d31 tends to decrease, and a sufficient amount of displacement as a piezoelectric ceramic composition tends not to be obtained. In addition to this, when z is outside the range of 0.45 ≦ z ≦ 0.55, Qm increases, so that the difference between the peak and the dip increases in the frequency-sound pressure characteristics, and the sound quality may be deteriorated. . Therefore, it is also necessary to satisfy 0.005 ≦ x ≦ 0.08, 0.03 ≦ y ≦ 0.15, and 0.45 ≦ z ≦ 0.55.

  Thus, a, x, y, and z are 0.97 ≦ a ≦ 1.03, 0.005 ≦ x ≦ 0.08, 0.03 ≦ y ≦ 0.15, and 0.45 ≦ z ≦ 0. By including the composite perovskite compound satisfying .55, a piezoelectric ceramic composition having a large piezoelectric d constant and a low mechanical quality factor Qm can be realized.

  In addition, the ratio of the metal element contained in a piezoelectric ceramic composition can be measured, for example using ICP analysis or a fluorescent X ray analysis, and using an atomic absorption analysis together as needed.

In the piezoelectric ceramic composition of the present embodiment, for example, a predetermined amount of each raw material powder of PbO, ZrO ₂ , TiO ₂ , Yb ₂ O ₃ , ZnO, and WO ₃ is weighed as a raw material, and wet-mixed for 10 to 24 hours using a ball mill or the like. The mixture is then dried and calcined at 600 to 800 ° C. for 1 to 3 hours, and the calcined product is pulverized again with a ball mill or the like. Thereafter, an organic binder is mixed into the pulverized product, a molded body is prepared by a known molding method such as press molding or a doctor blade method, and these are baked at 950 to 1250 ° C. for 1 to 3 hours in the air. It is done.

  Here, in the piezoelectric ceramic composition of the present embodiment, at least one of Al, Si, and Na as subcomponents is 0.001 part by mass ≦ Al ≦ 0 with respect to 100 parts by mass of the composite perovskite compound. .3 parts by mass, 0.005 parts by mass ≦ Si ≦ 0.06 parts by mass, and 0.01 parts by mass ≦ Na ≦ 0.2 parts by mass.

  With respect to the Al content, if the composite perovskite compound is in the range of 100 parts by mass or more and 0.3 parts by mass or less, fluctuations in the piezoelectric d constant under high temperature and high humidity and in the cooling and heating cycle can be suppressed.

  Further, if the Si amount is within the range of 0.005 parts by mass or more and 0.06 parts by mass or less with respect to 100 parts by mass of the composite perovskite compound, the fluctuation of the piezoelectric d constant under high temperature and high humidity is suppressed can do.

  In addition, when the Na amount is within the range of 0.01 parts by mass or more and 0.2 parts by mass or less with respect to 100 parts by mass of the composite perovskite compound, the piezoelectric d constant at high temperature and high humidity and in the cold cycle. Fluctuations can be suppressed.

  Note that at least a part of the Al and Na may be dissolved in the composite perovskite compound. For example, when Al dissolves as a trivalent ion at the B site of the composite perovskite compound, oxygen vacancies are generated and sintering is promoted. Further, Na is dissolved as a monovalent ion at the A site of the composite perovskite compound, whereby oxygen vacancies are generated and sintering is promoted. For this reason, the densification of the porcelain is improved and the intrusion of moisture from the grain boundary can be prevented, which is effective in suppressing the fluctuation of the piezoelectric d constant under high temperature and high humidity.

  Moreover, when oxygen vacancies are generated when Al is dissolved as trivalent ions or Na is dissolved as monovalent ions, a pinning effect acts on the domain wall (domain wall), and the domain wall (domain) Since the fluctuation of the wall) can be suppressed, it is effective to suppress the fluctuation of the piezoelectric d constant in the cooling cycle.

In addition, Si becomes a liquid phase at the grain boundary as SiO ₂ , so that the diffusion rate is improved and sintering is promoted. Therefore, since the sinterability of the piezoelectric ceramic produced by the piezoelectric ceramic composition of the present embodiment is improved and the intrusion of moisture from the grain boundary can be prevented, the fluctuation of the piezoelectric d constant under high temperature and high humidity is suppressed. It is effective.

  Furthermore, in the piezoelectric ceramic composition of the present embodiment, a part of Pb which is the A site of the composite perovskite compound is substituted with at least one of Ba, Sr, and Ca, and the total amount of substitution is The molar ratio may be 0.16 or less.

In this case, the composite perovskite compound in the piezoelectric ceramic composition has a general formula of (Pb _a-b-c-d Ba _b Src _{C a d} ) (Yb _2/3 W _1/3 ) _x (Zn _1/2 W _1/2 ) _y (Ti _z Zr _1-z ) _1-xy O ₃ and a, b, c, d at this A site satisfy 0.97 ≦ a + b + c + d ≦ 1.03 Is.

By substituting a part of Pb with at least one of Ba, Sr, and Ca, strain can be provided in the crystal lattice, and polarization inversion of the PZT material is easily induced. Therefore, the fluctuation of the resonance frequency due to temperature change can be reduced and the piezoelectric characteristics can be improved. If the sum of the substitution amounts of Ba, Sr, and Ca exceeds 0.16 in terms of molar ratio, the piezoelectric constant d31 tends to decrease, and a sufficient displacement amount as a piezoelectric ceramic composition tends not to be obtained. Moreover, there exists a tendency for the effect which reduces the change rate of the resonant frequency of a thermal cycle to become difficult to be acquired.

  The above-described piezoelectric ceramic composition can be used for a piezoelectric element. Next, an example of the piezoelectric element of this embodiment will be described.

  FIG. 1A is a schematic perspective view showing an example of the piezoelectric element of the present embodiment, and FIG. 1B is a schematic cross-sectional view taken along the line AA shown in FIG.

  The piezoelectric element 1 of this embodiment is formed by laminating a piezoelectric layer 11 made of the above-described piezoelectric ceramic composition and an internal electrode layer 12 made of a conductor containing 90% by mass or more of Ag. More specifically, a laminate 13 having a rectangular shape in plan view in which a plurality of piezoelectric layers 11 and a plurality of internal electrodes 12 are laminated, and a connection electrode that connects one end of each of the plurality of internal electrodes 12 every other layer. 14, and a surface electrode 15 electrically connected to the plurality of internal electrodes 12 by the connection electrode 14.

  The laminated body 13 is a plate-like body whose main surface viewed from the plane (upper surface) has a rectangular shape.

  The plurality of piezoelectric layers 11 constituting the multilayer body 13 uses the above-described piezoelectric ceramic composition, and the thickness of one layer of the piezoelectric layer 11 is, for example, 0.01 to 0.1 mm in order to drive at a low voltage. Set to

  The plurality of internal electrodes 12 constituting the multilayer body 13 are alternately stacked with the plurality of piezoelectric layers 11 to sandwich the piezoelectric layers 11 from above and below, and the piezoelectric layers 11 sandwiched between them are sandwiched between the piezoelectric layers 11. A drive voltage is applied. The plurality of internal electrodes 12 shown in FIG. 1 include first internal electrodes 121 and second internal electrodes 122 provided alternately. As these materials, for example, a conductor mainly composed of silver or silver-palladium suitable for low-temperature firing, or a conductor containing copper, platinum, or the like can be used. Good. In particular, it is preferably made of a conductor containing 90% by mass or more of silver so that low-temperature firing is possible.

  1 includes a first surface electrode 151 electrically connected to the first internal electrode 121 and a second surface electrode electrically connected to the second internal electrode 122. 152. The surface electrode 15 is provided on at least one main surface of the laminate 13, and in the example shown in FIG. 1, the first surface electrode 151 is provided on both main surfaces of the laminate 13, and the second surface electrode 152 is It is provided only on one main surface (upper main surface) of the laminate 13. By providing the first surface electrode 151 on the main surface, the outermost piezoelectric layer 11 of the multilayer body 13 is sandwiched between the internal electrode 122 and the first surface electrode 151, and the outermost piezoelectric layer 11. A driving voltage can be applied to the piezoelectric element to contribute to the vibration of the piezoelectric element. As a material for forming the first surface electrode 151 and the second surface electrode 152, silver, a silver compound containing silver or a glass containing silica as a main component, nickel, or the like can be used.

  The stacked body 13 is provided with connection electrodes 14 that connect one end of the plurality of internal electrodes 12 every other layer. Specifically, the first connection electrode 141 that electrically connects the first internal electrode 121 and the first surface electrode 151, and the second internal electrode 122 and the second surface electrode 152 are electrically connected. The second connection electrode 142 is included. In FIG. 1, a first connection electrode 141 and a second connection electrode 142 are provided on the side surface of the stacked body 13, more specifically, on the opposing end surface of the rectangular plate-shaped stacked body 13. As a material for forming the connection electrode 14, a silver compound, nickel, or the like containing silver or glass containing silica as a main component, similar to the surface electrode 15, can be used.

  In FIG. 1, the connection electrode 14 that electrically connects the surface electrode 15 and the internal electrode 12 is a side electrode formed on the end face of the layer body 13, but instead of the side electrode, an internal electrode layer is provided. 12 may be a through conductor penetrating through one end of the piezoelectric layer 11 and the piezoelectric layer 11. At this time, the other end portion of the second internal electrode 122 and the stacked body 13 are arranged so that the through conductor electrically connected to the first internal electrode 121 is not electrically connected to the second internal electrode 122. A desired gap may be provided between the end face and the end face.

  In addition, the piezoelectric element is not limited to the laminated structure as in the present example, and may have a configuration in which electrodes are provided on both main surfaces of a single-layer piezoelectric body.

  The piezoelectric element 1 having a piezoelectric layer made of a piezoelectric ceramic composition having a large piezoelectric d constant and a low mechanical quality factor Qm can be reduced in cost by low-temperature firing at 1000 ° C. or less and has a large piezoelectric characteristic. It becomes a piezoelectric element. Moreover, it can have a large displacement and a large generated force.

  The above-described piezoelectric element can be used for a piezoelectric vibration device. Next, an example of the piezoelectric vibration device of the present embodiment will be described.

  FIG. 2 is a schematic perspective view showing an example of the piezoelectric vibration device of the present embodiment. The piezoelectric vibration device 10 of the present embodiment has the piezoelectric element 1 described above and the piezoelectric element 1 attached thereto. A diaphragm 2 that vibrates due to the vibration of the element 1 is provided.

  The piezoelectric element 1 is an exciter that excites the diaphragm 2 by vibrating under application of a voltage. The main surface of the piezoelectric element 1 and the main surface of the diaphragm 2 are made of an adhesive such as an epoxy resin, both surfaces. When the piezoelectric element 1 is bent and vibrated by being joined by a tape or the like, the piezoelectric element 1 can give a certain vibration to the diaphragm.

  The diaphragm 2 vibrates together with the piezoelectric element 1 due to the vibration of the piezoelectric element 1.

  The diaphragm 2 can be formed using various materials such as resin and metal, and is composed of, for example, a resin plate such as polycarbonate or acrylic having a thickness of 10 to 500 μm, a metal plate such as SUS or brass, or a glass plate. be able to. The shape of the diaphragm 2 is not particularly limited, and may be a circular plate shape or an elliptical plate shape other than a polygonal plate shape such as a rectangular plate shape.

  The use of such a piezoelectric vibration device 10 is not limited as long as it vibrates the diaphragm 2. For example, the piezoelectric vibration device 10 can be used as an acoustic generator that generates sound by vibration. For example, it may be used for an electronic device such as a portable terminal, and a part of the casing of the portable terminal or a display cover may function as the diaphragm 2.

  The piezoelectric vibration device according to the present embodiment is configured using the piezoelectric element 1 including a piezoelectric layer made of a piezoelectric ceramic composition having a large piezoelectric d constant and a low mechanical quality factor Qm. When used as a generator, it can have high sound pressure and high sound quality.

  Examples of piezoelectric elements will be described below.

  A piezoelectric element provided with a piezoelectric body made of the piezoelectric ceramic composition of the present embodiment was manufactured as follows.

Specifically, PbO, ZrO ₂ , TiO ₂ , Yb ₂ O ₃ , ZnO, WO
₃ Each raw material powder of the percentage of each component of the sintered body is weighed in predetermined amounts as shown in Table 1, were wet mixed in a ball mill using ZrO ₂ balls, dried, 3 hours calcined at 700 ° C. The calcined product is pulverized again with a ball mill. Thereafter, an organic binder was mixed with the pulverized product, and the obtained powder was press-molded into a disc having a diameter of 16 mm and a thickness of 2 mm at a pressure of 1.5 t / cm ² . Furthermore, these molded bodies were degreased at 700 ° C. for 3 hours, sealed in a container made of MgO, and fired at 1050 ° C. in the atmosphere for 3 hours.

  The obtained sintered body was polished to form a disc having a thickness of 1.0 mm. Further, this circular plate was cut by dicing to obtain a rectangular plate-shaped piezoelectric body having a length of 12 mm, a width of 3 mm, and a thickness of 1 mm. Electrodes were formed by baking Ag paste on both main surfaces of the piezoelectric body, and a piezoelectric element was fabricated by applying a DC voltage of 2.5 kV / mm for 10 minutes in silicon oil at 80 ° C. for 10 minutes. The piezoelectric constants d31 and Qm were evaluated for this piezoelectric element.

As measurement items, a is the length in the long side direction of the rectangular plate piezoelectric element, b is the length in the short side direction of the rectangular plate piezoelectric element, t is the thickness of the rectangular plate piezoelectric element, and ρ is the sintered body. The piezoelectric constants d31 and Qm obtained from these were evaluated, with Cp as the electrostatic capacity for a frequency of 1 kHz, Fr as the resonance frequency, Fa as the antiresonance frequency, and R as the resonance resistance.

Specifically, a, b, and t are measured using a micrometer, ρ is measured using the Archimedes method, and Cp, Fr, Fa, and R are measured using an impedance / gain phase analyzer. Piezoelectric constant d obtained from numerical values of a, b, t, ρ, Cp, Fr, Fa
31 was evaluated. Moreover, the mechanical quality factor Qm calculated | required from the numerical value of Cp, Fr, Fa, R was evaluated.

  In addition, d31 [pm / V] is a good result when it is a high value of 230 or more, and a mechanical quality factor Qm is a good result when it is a low value of 60 or less. did. The results are shown in Tables 1 and 2.

  In addition, some samples were subjected to a high temperature and high humidity test and a cold cycle test. Specifically, a high-temperature and high-humidity test of 85 ° C., 85%, and a durability time of 1000 h, and a thermal cycle test of 1000 cycles at −55 ° C. for 30 minutes and 105 ° C. for 30 minutes were performed.

  Moreover, the temperature change of the resonance frequency was measured. Specifically, the resonance frequency before the high-temperature and high-humidity test or the thermal cycle test is Fr, and the resonance frequency after the test is Fr ′. The temperature change ΔFr [%] of the resonance frequency was obtained by ΔFr = 100 * | Fr′−Fr | / Fr. Fr and Fr ′ were measured using an impedance analyzer.

  These results are shown in Tables 1 and 2. In the evaluation results, items that were not measured were displayed as hyphens. In addition, regarding the substitution of Pb, those not substituted are indicated by a hyphen. In addition, those not including Al, Si, and Na are indicated by hyphens.

  According to Tables 1 and 2, it can be seen that a piezoelectric element including a piezoelectric body made of the piezoelectric ceramic composition of the present embodiment can achieve a large piezoelectric d constant and a low mechanical quality factor Qm.

  In addition, with respect to 100 parts by mass of the composite perovskite compound, at least one of Al, Si, and Na is 0.001 parts by mass ≦ Al ≦ 0.3 parts by mass, 0.005 parts by mass ≦ Si ≦ 0.06. When the mass ratio is out of the range of the ratio of 0.01 mass part ≦ Na ≦ 0.2 mass part, the change rate of d31 before and after the high-temperature and high-humidity test Δd31 (1), d31 before and after the cooling cycle test It was confirmed that the rate of change Δd31 (2) tends to be high.

  Further, when a part of Pb is substituted with at least one of Ba, Sr, and Ca, and the total substitution amount is substituted with a molar ratio exceeding 0.16, the temperature change of the resonance frequency is It has been confirmed that it becomes higher than 0.1%.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric element 11 ... Piezoelectric layer 12 ... Internal electrode layer 121 ... 1st internal electrode layer 122 ... 2nd internal electrode layer 13 ... Laminated body 14 ... Connection electrode 141 ... first connection electrode 142 ... second connection electrode 15 ... surface electrode 151 ... first connection electrode 152 ... second connection electrode 2 ... diaphragm 10 ... Piezoelectric vibration device

Claims (5)

The general formula is
_{Pb a (Yb 2/3 W 1/3)} x (Zn 1/2 W 1/2) y (Ti z Zr 1-z) 1-x-y O 3
Where a, x, y, z are
0.97 ≦ a ≦ 1.03
0.005 ≦ x ≦ 0.08
0.03 ≦ y ≦ 0.15
0.45 ≦ z ≦ 0.55
A piezoelectric ceramic composition comprising a composite perovskite compound satisfying At least one of Al, Si, and Na with respect to 100 parts by mass of the composite perovskite compound,
0.001 part by mass ≦ Al ≦ 0.3 part by mass 0.005 part by mass ≦ Si ≦ 0.06 part by mass 0.01 part by mass ≦ Na ≦ 0.2 part by mass 1. The piezoelectric ceramic composition according to 1.   The part of Pb is substituted with at least one of Ba, Sr, and Ca, and the total amount of substitution is 0.16 or less in molar ratio. The piezoelectric ceramic composition as described.   A piezoelectric element comprising a piezoelectric layer made of the piezoelectric ceramic composition according to any one of claims 1 to 3 and an internal electrode layer. A piezoelectric vibration device comprising: the piezoelectric element according to claim 4; and a vibration plate to which the piezoelectric element is attached and vibrates by vibration of the piezoelectric element.

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