JP2012062215A - Piezoelectric ceramic material and piezoelectric actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic material and a piezoelectric actuator, which have high displacement characteristics, are little affected by a pyroelectric effect, and assure a short capacitance stabilization time.SOLUTION: The piezoelectric ceramic material is represented by composition formula: aPbTiO-bPbZrO-cPb(NiNb)O-dPb(SbNb)O-ePb(CoNb)O, wherein a+b+c+d+e=100, b/(a+b)=(0.41 to 0.49), c is 20-30 mol%, d is 0.2-2 mol%, and e is 2-10 mol%.

Description

  The present invention relates to a piezoelectric ceramic material and a piezoelectric actuator.

  Conventionally, piezoelectric actuators have been widely used for precision control of semiconductor manufacturing and industrial equipment. Piezoelectric actuators with low power consumption, compactness, and high-speed and precise operation are not limited to conventional industrial applications, but are also being used in consumer applications such as mobile phones and digital cameras.

  In particular, recent camera modules and digital cameras mounted on mobile phones are becoming smaller in size, increasing the number of pixels in search of more delicate image quality, and products that have a high zoom function even though they are small have appeared. .

  Along with such high functionality of digital cameras, piezoelectric actuators are used as lens driving sources. A piezoelectric actuator used for driving a lens is required to have performance such as large displacement characteristics, being hardly affected by ambient temperature changes, and having high thermal shock resistance.

  A piezoelectric actuator is a device that generates a mechanical displacement according to an input voltage. Therefore, it is preferable that the piezoelectric element constituting the piezoelectric actuator generate a larger displacement with less electrical energy.

The piezoelectric d constant is used as one of the indicators of the displacement characteristics of the piezoelectric element, which is determined by the relative dielectric constant ε _r and the electromechanical coupling coefficient K of the piezoelectric element. Among these, the relative dielectric constant ε _r is an important parameter for determining the electrostatic capacitance C of the piezoelectric element, and is an important index in designing a power supply circuit for driving the piezoelectric actuator.

However, the relative dielectric constant ε _r of the piezoelectric element varies depending on the material composition and the manufacturing method, and also varies depending on the temperature of the piezoelectric element. When designing a power supply circuit for driving a piezoelectric actuator, it is necessary to consider the temperature characteristics of the relative permittivity ε _r and to design the actual use environment of the device.

Mobile phones and digital cameras typified by consumer use are expected to undergo a rapid temperature change in an actual usage environment, for example, when moving from indoors to outdoors. When a sudden temperature change is applied to the piezoelectric element, a pyroelectric effect is generated in which charges are generated on the surface of the element due to a change in the magnitude of polarization. The electric field Ep is generated by the pyroelectric charge Qp generated by the pyroelectric effect, and the value of the relative permittivity ε _r changes due to the nonlinear effect of dielectric characteristics, the fine structure of the crystal, the microscopic movement of the polarization domain, and the like.

FIG. 6 is a diagram schematically showing the change in the capacitance C when the temperature of the piezoelectric element changes. Rapid temperature changes occur, the rapid temperature changes in the piezoelectric element is provided, in addition to the change ΔC1 in the capacitance C with temperature characteristics of the conventional dielectric constant epsilon _r, the external generated by pyroelectric charge Qp A capacitance change ΔC2 due to the electric field Ep occurs. Capacitance change ΔC2 by the external electric field Ep is the relative dielectric constant epsilon _r change in due to the nonlinear effect of the piezoelectric elements, and the microstructure of the crystals in the micro region, considered to be due to the movement of the polarization domain, Ya material composition The influence varies depending on the density of the crystal grains due to the difference in the manufacturing method.

  The capacitance change ΔC2 caused by the pyroelectric effect due to this rapid temperature change converges with time.

  Here, the capacitance stabilization time Ts is a time until the capacitance change ΔC2 is stabilized at a capacitance value within 1% with reference to the capacitance 240 hours after the sudden temperature change. It is defined as This capacitance stabilization time Ts varies depending on the piezoelectric ceramic material, and there are some that converge on the order of several minutes, and others that require several tens of hours.

  So far, means for leaking the pyroelectric charge Qp has been used to prevent the influence of the pyroelectric effect due to a rapid temperature change.

  For example, Patent Document 1 proposes a multilayer ceramic piezoelectric drive circuit in which charge leakage means is provided in parallel to a multilayer ceramic piezoelectric body to remove charges generated by the pyroelectric effect and prevent polarization degradation.

Further, Patent Literature 2, Patent Literature 3 and the like are disclosed as conventional piezoelectric ceramic materials. Patent Document 2 proposes a material that suppresses fluctuations in sensitivity due to a rapid temperature change by using a piezoelectric ceramic material represented by aPbTiO ₃ —bPbZrO ₃ —cPb (Co _1/3 Nb _2/3 ) O ₃ .

In Patent Document 3, Pb [(Ni _1/3 Nb _2/3 ) _A (Sb _1/2 Nb _1/2 ) _B Zr _C Ti _D ] O ₃ (provided that A + B + C + D = 1) and La as a subcomponent Large mechanical displacement characteristics can be obtained by adding one selected from rare earth oxides such as ₂ O ₃ , CeO ₂ , Nd ₂ O ₃ , Sm ₂ O ₃ , and Dy ₂ O ₃ and Co ₂ O _3. The resulting piezoelectric ceramic composition has been proposed.

JP-A-60-249877 Japanese Patent Laid-Open No. 11-92223 Japanese Patent Laid-Open No. 61-10287

  The charge leakage means of Patent Document 1 is applied on the circuit side that drives the multilayer ceramic piezoelectric body. For example, the circuit configuration is such that a relay circuit is installed in parallel with the multilayer ceramic piezoelectric body, and the resistance value of the charge leakage path is low during the period in which the multilayer ceramic piezoelectric body is stopped.

  However, in the configuration of Patent Document 1, the number of parts of the drive circuit that drives the multilayer ceramic piezoelectric body increases, and the cost and size of piezoelectric device modules such as piezoelectric actuators are expected to increase. As the application of piezoelectric actuators to consumer applications progresses, it is a major drawback that the module itself becomes large, especially when considering mounting a small camera on a mobile phone or the like.

In the piezoelectric ceramic material of Patent Document 2, Pb (Co _1/3 Nb _2/3 ) O ₃ is dissolved as a third component in a solid solution of aPbTiO ₃ —bPbZrO ₃ and Sm ₂ O ₃ is further added. Thus, the mechanical quality factor Qm and the resonance frequency fr have characteristics with little variation with respect to temperature change. If the thermal shock resistance of the mechanical quality factor Qm and the resonance frequency fr is strong, the noise component of the piezoelectric gyro is reduced, and a highly sensitive gyro can be realized. However, although this material has high temperature stability, it is not suitable for actuator applications that require high displacement characteristics.

In Patent Document 3, a material of Pb [(Ni _1/3 Nb _2/3 ) _A (Sb _1/2 Nb _1/2 ) _B Zr _C Ti _D ] O ₃ is used with rare earth elements and Co ₂ O ₃ as subcomponents. When added, a large displacement characteristic can be obtained. On the other hand, the relative dielectric constant ε _r of the material has a detrimental effect that the temperature change rate becomes large.

When the temperature change rate of the relative permittivity ε _r is large, the stabilization time of the element capacitance caused by the temperature change also becomes long, and the capacitance stabilization time Ts after the capacitance change caused by the rapid temperature change is: There was a problem that the more rare-earth elements and Co ₂ O ₃ which are sub-components were added, the worse it was.

  When the capacitance stabilization time Ts takes several tens of hours, various problems occur during the manufacture and actual use of piezoelectric devices such as piezoelectric actuators. For example, when designing a power supply circuit for driving a piezoelectric actuator, the constants of the peripheral circuits are determined using the value of the capacitance C of the piezoelectric element constituting the piezoelectric actuator as an index. If there is a difference between the value at the time of circuit design and the value of the capacitance in actual use, there arises a problem that the operation does not work as designed.

  Further, at the stage of product inspection of the piezoelectric element, capacitance measurement is performed in order to detect a short circuit defect of the element and an abnormal electrical characteristic product. In order to measure the correct capacitance value, for example, heat treatment must be performed in the element manufacturing process, and then the device must wait for the capacitance stabilization time Ts, which causes a significant reduction in manufacturing efficiency. .

  In addition to the problem that when the temperature of the piezoelectric element changes abruptly, it takes a certain amount of time for the capacitance C to stabilize, there is also a problem of polarization degradation due to the pyroelectric effect.

  Normally, when the temperature of the piezoelectric element rises, the external electric field Ep due to the pyroelectric charge Qp works in a direction that strengthens the polarization of the element, but when the temperature of the piezoelectric element falls, the direction of the external electric field Ep is a direction that degrades the polarization. To work. Therefore, if the rapid temperature change is repeated, the polarization of the piezoelectric element deteriorates, the electromechanical coupling coefficient K decreases, and the displacement characteristics deteriorate. These problems caused by the rapid temperature change of the piezoelectric element are a major issue with respect to the stability of the performance of a piezoelectric actuator using the piezoelectric element.

  The present invention solves the above-described problems, and an object thereof is to provide a piezoelectric ceramic material and a piezoelectric actuator that have high displacement characteristics, are less affected by the pyroelectric effect, and have a short capacitance stabilization time.

The present invention is a composition formula _{aPbTiO 3 -bPbZrO 3 -cPb (Ni 1/3} Nb 2/3) O 3 -dPb (Sb 1/2 Nb 1/2) O 3 -ePb (Co 1/3 Nb 2/3 ) O ₃ (where a + b + c + d + e = 100) and a piezoelectric actuator using the piezoelectric ceramic material.

That is, according to the present invention, composition formula _{aPbTiO 3 -bPbZrO 3 -cPb (Ni 1/3} Nb 2/3) O 3 -dPb (Sb 1/2 Nb 1/2) O 3 -ePb (Co 1 / ₃ Nb _2/3 ) O ₃ (where a + b + c + d + e = 100), b / (a + b) is 0.41 to 0.49, c is 20 to 30 mol%, d is 0.2 to 2 mol%, e A piezoelectric ceramic material characterized in that is 2 to 10 mol% is obtained.

  In addition, according to the present invention, a piezoelectric actuator made of the above piezoelectric ceramic material can be obtained.

  By using the piezoelectric ceramic material of the present invention, it is possible to provide a piezoelectric ceramic material and a piezoelectric actuator that have high displacement characteristics, are less affected by the pyroelectric effect, and have a short capacitance stabilization time.

It is a figure which shows the result of having compared the capacitance stabilization time Ts. It is a figure which shows the value of the insulation resistance IR in the 25 degreeC environment of the sample using the piezoelectric ceramic material of this invention. It is a figure which shows the value of the mechanical quality factor Qm of the sample which uses the piezoelectric ceramic material of this invention. PbTiO a graph showing the relation ₃ and content ratio b / PbZrO ₃ for PbZrO ₃ (a + b) and radial electromechanical coupling factor _{K r.} It is a diagram showing the relationship between the content ratio c and the Curie point Tc of _{Pb (Ni 1/3 Nb 2/3) O} 3. It is a figure which shows typically the change of the electrostatic capacitance C when the temperature of a piezoelectric element changes. FIGS. 7A and 7B are diagrams schematically showing the pyroelectric effect and the change in capacitance. FIG. 7A shows a state where the insulation resistance IR is low, and FIG. 7B shows a state where the insulation resistance IR is high. is there. FIG. 8A is a perspective view showing an electrode structure of a piezoelectric actuator, FIG. 8A shows a partial electrode structure, and FIG. 8B shows a full-surface electrode structure.

The present invention composition formula _{aPbTiO 3 -bPbZrO 3 -cPb (Ni 1/3} Nb 2/3) O 3 -dPb (Sb 1/2 Nb 1/2) O 3 -ePb (Co 1/3 Nb 2 / ₃ ) O ₃ (where a + b + c + d + e = 100), b / (a + b) is 0.41 to 0.49, c is 20 to 30 mol%, d is 0.2 to 2 mol%, e is 2 to 10 mol It is a piezoelectric ceramic material consisting of the main component.

In general, a piezoelectric ceramic material can improve dielectric and piezoelectric characteristics that cannot be obtained by a two-component system by dissolving one or more composite perovskite compounds in a PbTiO ₃ -PbZrO ₃ binary PZT ceramic. Has been widely used.

In particular, when considered as a material for a piezoelectric actuator, the displacement characteristic is one of the most important characteristics. Therefore, in the present invention, Pb (Ni _1/3 Nb _2/3 ) O ₃ , Pb (Sb _1/2 Nb _1/2 ) O ₃ is dissolved to provide a large relative dielectric constant ε _r and a high electromechanical coupling. The coefficient K is obtained, and a high displacement characteristic in which the piezoelectric d constant d ₃₃ is 400 pm / V or more can be realized.

Further, by dissolving Pb (Co _1/3 Nb _2/3 ) O ₃ , a material having a low insulation resistance IR and a large mechanical quality factor Qm is formed. As a result, when the capacitance changes due to a rapid temperature change of the element, the time until the capacitance becomes stable is shortened. Conventional actuator materials generally have an insulation resistance IR value of about several thousand MΩ to several tens of thousands MΩ, but Pb (Co _1/3 Nb _2/3 ) O ₃ is dissolved. Thus, the insulation resistance IR value at room temperature can be reduced to several hundred MΩ.

  FIG. 7 is a diagram schematically showing the pyroelectric effect and the change in capacitance. FIG. 7A shows a state where the insulation resistance IR is low, and FIG. 7B shows a state where the insulation resistance IR is high. FIG. In FIG. 7, the piezoelectric body 13 provided with the first electrode 11 and the second electrode 12 is polarized like a polarization direction 14. The state where the insulation resistance IR is low in FIG. 7A is considered to have the leak path 15 schematically. The pyroelectric charge Qp generated by the rapid temperature change is offset by the leak path 15 between the positive pyroelectric charge and the negative pyroelectric charge. For this reason, the external electric field Ep due to the pyroelectric charge Qp is small, and the piezoelectric body 13 is hardly affected by the external electric field Ep.

On the other hand, when the insulation resistance IR in FIG. 7B is high, a large amount of pyroelectric charge Qp remains in the first electrode 11 and the second electrode 12, and the external electric field Ep generated thereby increases. . For this reason, the relative permittivity ε _{r of the} entire device changes greatly due to the nonlinear effect of the dielectric characteristics, the fine structure of the crystal in the microscopic region, and the movement of the polarization domain. As the relative permittivity ε _r changes greatly, the capacitance C also changes greatly.

  That is, by reducing the insulation resistance IR, the change in capacitance is small, and the capacitance stabilization time Ts is shortened. Although the insulation resistance is reduced as compared with the prior art, the insulation resistance IR value sufficient to function as an insulator is maintained.

Furthermore, by dissolving Pb (Co _1/3 Nb _2/3 ) O ₃ , the mechanical quality factor Qm is increased and the capacitance stabilization time Ts is shortened. The capacitance stabilization time Ts tends to be shorter as the mechanical quality factor Qm increases. This is because the fine structure of the crystal and the polarization domain become difficult to move due to the increase in the Qm of the material. Conceivable.

PbO, TiO ₂ , ZrO ₂ , Co ₃ O ₄ , Nb ₂ O ₅ , NiO, and Sb ₂ O ₃ were weighed so as to have a target composition as the main component raw materials. This raw material powder was placed in a nylon pod together with zirconia balls and wet mixed for 46 hours. This mixed powder was dehydrated and dried, and then pre-baked in an alumina bowl for 2 hours at 850 ° C. This pre-baked powder was wet pulverized with zirconia balls in a nylon pod for 20 hours. Subsequently, it was dehydrated and dried, and a binder was mixed with the obtained pre-fired pulverized powder and pressed to form φ20 × 10 mm. This molded body was sintered at 1000 to 1200 ° C. and processed into a disk having a thickness of 1 mm with an outer peripheral cutting machine. And silver paste was apply | coated on both surfaces of the processed disk, and it baked at 450 degreeC, the electrode was formed, and it was set as the sample. The sample thus obtained was subjected to a polarization treatment in silicon oil at 100 ° C., 2 kV / mm for 15 minutes, and then returned to an environment at room temperature of 25 ° C.

Example 1
In the manner described _{above, aPbTiO 3 -bPbZrO 3 -cPb (Ni} 1/3 Nb 2/3) O 3 -dPb (Sb 1/2 Nb 1/2) O 3 -ePb (Co 1/3 Nb 2/3) Each composition of O ₃ is b / (a + b) = 0.44, c = 25 mol%, d = 0.4 mol%, and the content ratio e of Pb (Co _1/3 Nb _2/3 ) O ₃ is 5 mol%. Samples changed to 10 mol% were prepared. As comparison _material, the respective compositions of _{aPbTiO 3 -bPbZrO 3 -cPb (Ni 1/3} Nb 2/3) O 3 -dPb (Sb 1/2 Nb 1/2) O 3, b / (a + b) = 0. 44, c = 25 mol%, d = 0.4 mol%, and those not containing Pb (Co _1/3 Nb _2/3 ) O ₃ were prepared.

  Next, the change in the capacitance of the sample was measured when a sudden temperature change from 100 ° C. to 25 ° C. was applied to the polarized sample. FIG. 1 is a diagram showing a result of comparing the capacitance stabilization time Ts. Here, the horizontal axis represents the capacitance stabilization time Ts, and the vertical axis represents the capacitance ratio when the capacitance after 240 hours from the temperature change is 1. As described above, until the capacitance value stabilizes within 1% (capacitance ratio: 1.01) based on the capacitance after 240 hours from the sudden temperature change. Time is defined as capacitance stabilization time Ts.

  In the comparative material, the capacitance stabilization time Ts takes approximately 40 hours, whereas in the present invention, the capacitance is stable in less than one hour. As can be seen from FIG. 1, according to the present invention, the capacitance stabilization time Ts due to a rapid temperature change can be greatly improved.

  This improved factor can be roughly attributed to the insulation resistance IR of the material, the fine structure of the crystal in the microscopic region, and the ease of movement of the polarization domain.

FIG. 2 is a diagram showing a value of insulation resistance IR in a 25 ° C. environment of a sample using the piezoelectric ceramic material of the present invention. The vertical axis represents the insulation resistance IR, the horizontal axis represents the content ratio e of Pb (Co _1/3 Nb _2/3 ) O ₃ , and e was changed to 2 mol%, 5 mol%, and 10 mol%. As shown in FIG. 2, when 2 mol% or more of Pb (Co _1/3 Nb _2/3 ) O ₃ is contained, the value of the insulation resistance IR decreases to several hundred MΩ level in a 25 ° C. environment. It has been found that the value of the insulation resistance IR is further reduced when a high temperature environment is used. When the insulation resistance IR is lowered, the pyroelectric charge Qp generated by the rapid temperature change leaks to the electrode on the facing side through the piezoelectric body, and as a result is less affected by the pyroelectric effect. The shortening time Ts can be realized. When Pb (Co _1/3 Nb _2/3 ) O ₃ is contained in an amount of more than 10 mol%, the value of the insulation resistance IR becomes small and the performance as an insulator is inferior. Therefore, e needs to be 10 mol% or less. is there.

Further, the mechanical quality factor Qm tends to increase as the content ratio of Pb (Co _1/3 Nb _2/3 ) O ₃ increases. FIG. 3 is a diagram showing the value of the mechanical quality factor Qm of a sample using the piezoelectric ceramic material of the present invention. Here, the horizontal axis represents the content ratio e of Pb (Co _1/3 Nb _2/3 ) O ₃ , and the vertical axis represents the mechanical quality factor Qm. It was confirmed that the mechanical quality factor Qm was increased by increasing the content ratio of Pb (Co _1/3 Nb _2/3 ) O ₃ . This is considered that the capacitance stabilization time Ts is shortened because the crystal microstructure and the polarization domain are difficult to move.

(Example 2)
Example _{1 aPbTiO 3 -bPbZrO 3 -cPb (Ni} 1/3 Nb 2/3) in the same manner as _{O 3 -dPb (Sb 1/2 Nb 1/2} ) O 3 -ePb (Co 1/3 Nb 2 _/ 3) each composition of _{O 3, c = 25mol%,} d = 0.4mol%, e = a 5 mol%, PbTiO ₃ and the content ratio b / (a + b) 0.40 of PbZrO ₃ for PbZrO _3, Samples changed to 0.41, 0.43, 0.44, 0.45, 0.47, 0.49, and 0.50 were prepared. These samples were measured resonant frequency and the antiresonant frequency was calculated electromechanical coupling coefficient K _r in the radial direction from the measurement value.

FIG. 4 is a diagram showing the relationship between the content ratio b / (a + b) of PbTiO ₃ and PbZrO _{3 and} the electromechanical coupling coefficient K _{r in} the radial direction. A piezoelectric ceramic material for obtaining a large displacement characteristic is required to have a high electromechanical coupling coefficient. In the piezoelectric actuator application, the displacement characteristic is not satisfied unless the electromechanical coupling coefficient is ensured to be 50% or more. Thus, as seen from FIG. 4, the content ratio b / (a + b) of PbZrO ₃ for PbTiO ₃ and PbZrO ₃ is required to be 0.41 to 0.49.

Example 3
Example _{1 aPbTiO 3 -bPbZrO 3 -cPb (Ni} 1/3 Nb 2/3) in the same manner as _{O 3 -dPb (Sb 1/2 Nb 1/2} ) O 3 -ePb (Co 1/3 Nb 2 _{/ 3} ) The composition of O ₃ is b / (a + b) = 0.44, d = 0.4 mol%, e = 5 mol%, and the content ratio c of Pb (Ni _1/3 Nb _2/3 ) O ₃ Samples were prepared by changing the content to 20 mol%, 25 mol%, 30 mol%, 35 mol%, and 50 mol%, respectively. These samples were measured resonant frequency and the antiresonant frequency was calculated electromechanical coupling coefficient K _r in the radial direction from the measurement value.

FIG. 5 is a diagram illustrating the relationship between the content ratio c of Pb (Ni _1/3 Nb _2/3 ) O ₃ and the Curie point Tc. Increasing the content ratio c of Pb (Ni _1/3 Nb _2/3 ) O ₃ increases the relative dielectric constant ε _{r and} improves the displacement characteristics, but the Curie point Tc decreases as shown in FIG. Industrially, the piezoelectric ceramic material can be used only in an environment where the temperature used is limited. When used in consumer applications, the Curie point Tc needs to be 220 ° C. or higher, and as can be seen from FIG. 5, the content ratio c of Pb (Ni _1/3 Nb _2/3 ) O ₃ is 20-30 mol%. Is desirable. Further, when the content ratio c of Pb (Ni _1/3 Nb _2/3 ) O ₃ is less than 20 mol%, the displacement characteristics deteriorate, and therefore, c is preferably 20 mol% or more.

Example 4
Example _{1 aPbTiO 3 -bPbZrO 3 -cPb (Ni} 1/3 Nb 2/3) in the same manner as _{O 3 -dPb (Sb 1/2 Nb 1/2} ) O 3 -ePb (Co 1/3 Nb 2 _{/ 3} ) Samples with different composition ratios of O ₃ were prepared.

Table 1 shows the relative dielectric constant ε _r when the content ratio c of Pb (Ni _1/3 Nb _2/3 ) O _{3 and} the content ratio d of Pb (Sb _1/2 Nb _1/2 ) O ₃ are changed. The characteristics of the piezoelectric constant d ₃₃ and the Curie point Tc are shown. b / (a + b) = 0.44, c = 25 mol%, e = 5 mol%, and the content ratio d of Pb (Sb _1/2 Nb _1/2 ) O ₃ is changed from 0.1 mol% to 2.5 mol% I let you. Increasing the content ratio d of Pb (Sb _1/2 Nb _1/2 ) O ₃ increases the Curie point Tc, but decreases the relative dielectric constant ε _r and the piezoelectric constant d ₃₃ . When d exceeds 2 mol%, the piezoelectric constant d ₃₃ is smaller than 400 [pm / V], and the displacement characteristics as a piezoelectric actuator are not satisfied. On the other hand, if the content ratio d of Pb (Sb _1/2 Nb _1/2 ) O ₃ is less than 0.2 mol%, the Curie point Tc becomes lower than 220 ° C. and cannot be applied to a piezoelectric actuator for consumer use. Therefore, the content ratio d of Pb (Sb _1/2 Nb _1/2 ) O ₃ is preferably 0.2 to 2 mol%.

(Example 5)
represented by _{aPbTiO 3 -bPbZrO 3 -cPb (Ni 1/3} Nb 2/3) O 3 -dPb (Sb 1/2 Nb 1/2) O 3 -ePb (Co 1/3 Nb 2/3) O 3 Piezoelectric ceramic material was applied as a piezoelectric actuator.

  FIG. 8 is a perspective view showing an electrode structure of the piezoelectric actuator. FIG. 8A shows a partial electrode structure and FIG. 8B shows a full-surface electrode structure. In the piezoelectric actuator having the partial electrode structure shown in FIG. 8A, the piezoelectric layers 20 and the internal electrode layers 21 are alternately stacked, and the internal electrode layers 21 are exposed on every other side. An external electrode 22 is formed on the side surface, and is electrically connected to the exposed portion of the internal electrode layer 21. In the piezoelectric actuator having the entire surface electrode structure shown in FIG. 8B, the piezoelectric layers 20 and the internal electrode layers 21 are alternately stacked, and the internal electrode layers 21 are formed on the entire surface. Insulators 23 are formed on every other layer exposed on the side surface of the internal electrode layer, and external electrodes 22 are formed thereon. The internal electrode layer 21 in which the insulator 23 is not formed and the external electrode 22 are electrically connected every other layer. All of the piezoelectric actuators are often coated with insulating coating on the side surface to take measures against short circuit defects. In this example, a piezoelectric actuator having a partial electrode structure was produced.

PbO, TiO ₂ , ZrO ₂ , Co ₃ O ₄ , Nb ₂ O ₅ , NiO, and Sb ₂ O ₃ were weighed so as to have a target composition as the main component raw materials. In this _{embodiment, aPbTiO 3 -bPbZrO 3 -cPb (Ni} 1/3 Nb 2/3) O 3 -dPb (Sb 1/2 Nb 1/2) O 3 -ePb (Co 1/3 Nb 2/3) Each composition of O ₃ was b / (a + b) = 0.44, c = 25 mol%, d = 0.4 mol%, and e = 5 mol%. This raw material powder was placed in a nylon pod together with zirconia balls and wet mixed for 46 hours. This mixed powder was dehydrated and dried, and then pre-baked in an alumina bowl for 2 hours at 850 ° C. This pre-baked powder was wet pulverized with zirconia balls in a nylon pod for 20 hours. A slurry of this pre-fired pulverized powder was prepared by adding a mixture of a binder and a solvent. Using this slurry, a green sheet having a thickness of about 20 μm was prepared by a doctor blade method, and a conductive paste containing silver and palladium was pattern-printed and dried. Necessary areas of the green sheet on which the conductive paste was printed were cut, laminated, and pressed. After pressurization, heat treatment was performed to remove the binder, and sintering was performed at 1100 ° C. Thereafter, the external electrode was sputtered to cut the sintered body into a shape of 0.9 mm × 0.9 mm × 1.45 mm. Finally, the side surface where the internal electrodes of the laminated piezoelectric body after cutting were exposed was coated with insulation to take measures against short-circuit defects. The displacement amount of the piezoelectric actuator thus obtained was measured, and it was confirmed that a high displacement amount of 30 nm / V or more was obtained.

As the electrode structure of the piezoelectric actuator, an optimum structure is selected depending on the application and the required shape and size of the piezoelectric actuator. Since the full-surface electrode structure is not an intermittent electrode structure like a partial electrode, a larger displacement characteristic can be obtained with the same number of layers and shape dimensions. On the other hand, in the partial electrode structure, the manufacturing process is relatively simpler than that of the full-surface electrode structure, but stress is concentrated at the end portion of the internal electrode when the piezoelectric actuator is driven, and there is a possibility that the partial electrode structure may be damaged at a large displacement. In any of the electrode _{structure, aPbTiO 3 -bPbZrO 3 -cPb (Ni} 1/3 Nb 2/3) according to the invention _{O 3 -dPb (Sb 1/2 Nb 1/2} ) O 3 -ePb (Co 1/3 A piezoelectric ceramic material represented by Nb _2/3 ) O ₃ is applicable. In particular, the piezoelectric ceramic material of the present invention can be more effective in consumer applications that may be used in various temperature environments, such as small camera modules for mobile phones and lens modules for digital cameras.

DESCRIPTION OF SYMBOLS 11 1st electrode 12 2nd electrode 13 Piezoelectric body 14 Polarization direction 15 Leak path 20 Piezoelectric layer 21 Internal electrode layer 22 External electrode 23 Insulator

Claims (2)

Composition formula _{aPbTiO 3 -bPbZrO 3 -cPb (Ni 1/3} Nb 2/3) O 3 -dPb (Sb 1/2 Nb 1/2) O 3 -ePb (Co 1/3 Nb 2/3) O 3 (Where a + b + c + d + e = 100), b / (a + b) is 0.41 to 0.49, c is 20 to 30 mol%, d is 0.2 to 2 mol%, and e is 2 to 10 mol%. Piezoelectric ceramic material characterized by   A piezoelectric actuator comprising the piezoelectric ceramic material according to claim 1.

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