JP2018032725A - Method for driving piezoelectric ceramic and piezoelectric ceramic - Google Patents

Abstract

A large displacement amount can be obtained without impairing reliability even when continuously driven for a long time with a relatively high applied electric field.
In a piezoelectric ceramic, internal electrodes and ceramic layers are alternately laminated. The ceramic layer 2 contains a perovskite type compound (KNN compound) containing Nb and an alkali metal element as a main component, and the internal electrode 3 contains a base metal material such as Ni. The KNN compound preferably has a coercive electric field of 1 kV / mm or less and an electromechanical coupling coefficient k ₃₁ of 20% or less. The piezoelectric ceramic is driven by alternately and continuously applying an electric field having a polarity different from that of the coercive electric field by two or more times.
[Selection] Figure 1

Description

  The present invention relates to a piezoelectric ceramic driving method and a piezoelectric ceramic, and more particularly to a piezoelectric ceramic driving method using a lead-free piezoelectric material and a piezoelectric ceramic driven by this driving method.

  Conventionally, piezoelectric ceramic electronic parts such as an ultrasonic sensor, a piezoelectric buzzer, and a piezoelectric actuator using a piezoelectric material are widely known. In recent years, there has been an increasing demand for piezoelectric ceramic electronic components that are smaller in size and capable of acquiring a large amount of displacement.

For example, in Patent Document 1, the internal electrode has Ni as a main component and the ceramic layer has a general formula {(1-x) (K _1-ab Na _a Li _b ) (Nb _{1− c Ta c) O 3 -xM2M4O 3} } ( however, M2 is Ca, Ba, and at least one kind of Sr, M4 is Zr, Sn, and at least one kind of Hf, x, a , B, and c are respectively 0 ≦ x ≦ 0.06, 0 ≦ a ≦ 0.9, 0 ≦ b ≦ 0.1, and 0 ≦ c ≦ 0.3). And the piezoelectric ceramic composition is formed by adding 2α mol of Na, (α + β) mol of M4 ′ element (M4 ′ is at least one of Zr, Sn, and Hf) with respect to 100 mol of the main component. Any one element)), and γ mol of Mn, wherein α, β, and γ are respectively .1 ≦ α ≦ β, 1 ≦ α + β ≦ 10, and 0 piezoelectric ceramic electronic component of a multilayer which satisfies ≦ gamma ≦ 10 have been proposed.

In Patent Document 1, a piezoelectric ceramic composition is formed of an alkali metal niobate compound (hereinafter referred to as “KNN compound”), an internal electrode is formed of Ni, and co-fired in a reducing atmosphere. A laminated piezoelectric actuator having a longitudinal electromechanical coupling coefficient k ₃₁ of 10% or more and a piezoelectric constant d ₃₃ of 30 pC / N or more is obtained.

  In addition, a technology has been developed in which a lead zirconate titanate compound (hereinafter referred to as “PZT compound”) is used for the piezoelectric ceramic to improve the displacement.

For example, Patent Document 2 discloses a piezoelectric ceramic having a PZT-based perovskite structure, which includes Pb, Sr, Mg, Nb, Zr, and Ti as constituent elements, a relative dielectric constant of 3000 or more, and a piezoelectric constant d ₃₁ of There has been proposed a piezoelectric ceramic that has an applied reverse voltage of 670 V / mm or more that minimizes the insulation resistance when the voltage application holding time is 1 second at room temperature and 1 second.

  In this kind of piezoelectric ceramic, it is considered effective to widen the width of the applied electric field in order to obtain a large amount of displacement, but if an electric field higher than the coercive electric field is applied in the reverse direction, depolarization occurs, causing the piezoelectric displacement. I can't do that.

  Therefore, in Patent Document 2, an electric field less than the coercive electric field is applied in the reverse direction in addition to the forward direction, thereby expanding the width of the electric field that can be applied, thereby increasing the maximum displacement.

Japanese Patent No. 5556183 (Claim 1, paragraph [0093], etc.) Japanese Patent No. 5935187 (Claim 1 etc.)

  However, in Patent Document 1, when an electric field is continuously applied in the positive direction and unipolar driving is performed, if the electric field is 1 kV / mm or less, the piezoelectric displacement occurs even if continuous driving is performed for a long time, but 1 kV / mm is reduced. When a high electric field exceeding the above is applied and driven continuously for a long time, the insulation properties deteriorate and it becomes difficult to perform piezoelectric displacement.

  That is, the displacement amount of the piezoelectric ceramic is proportional to the product of the maximum electric field Emax that can be applied and the piezoelectric constant d. The piezoelectric constant d depends on the component composition of the piezoelectric material, and it is known that the KNN compound has a smaller piezoelectric constant d than the PZT compound. Therefore, in order to increase the amount of piezoelectric displacement by using the KNN compound for the piezoelectric ceramic, it is desirable to increase the maximum electric field Emax that can be applied.

  However, according to the experimental results of the present inventors, in Patent Document 1, when a high electric field exceeding 1 kV / mm is applied to perform unipolar driving, the insulating property is significantly deteriorated by long-time continuous driving, and a large displacement amount is obtained. On the contrary, it has been found that the decrease in the amount of piezoelectric displacement becomes conspicuous and the reliability also decreases.

  In Patent Document 2, a PZT compound is used and an electric field is applied in the opposite direction to increase the width of the electric field that can be applied to increase the amount of displacement. When an electric field is applied in the opposite direction, depolarization occurs and piezoelectricity disappears, so that only an electric field less than the coercive electric field can be applied. Therefore, in Patent Document 2, there is a limit to the width of the electric field that can be applied, and there is a limit to obtaining the displacement amount. In addition, the PZT compound has a large hysteresis of polarization-electric field characteristics, and due to such a large hysteresis, structural defects such as cracks are likely to occur when driven continuously for a long time, and the reliability is poor. In addition, since the PZT compound contains Pb, which is an environmentally hazardous substance, as a main component, it is not preferable from the viewpoint of the environment.

  The present invention has been made in view of such circumstances, and a piezoelectric ceramic driving method capable of obtaining a large displacement without impairing reliability even when continuously driven for a long time with a relatively high applied electric field, and An object is to provide a piezoelectric ceramic.

  KNN compounds are known to have a low coercive electric field and a small electromechanical coupling coefficient. Then, the present inventors use this KNN compound as a piezoelectric material, and simultaneously sinter the piezoelectric material and an internal electrode material mainly composed of a base metal material in a reducing atmosphere to produce a piezoelectric ceramic. As a result of research, by alternately applying an electric field with a polarity more than twice that of the coercive electric field to this piezoelectric ceramic, it is possible to drive continuously for a long time with a relatively high applied electric field, thereby increasing the amount of displacement. The knowledge that it can obtain and can ensure favorable reliability was acquired.

  The present invention has been made based on such knowledge, and the piezoelectric ceramic driving method according to the present invention is a piezoelectric ceramic driving method in which ceramic layers and internal electrodes are alternately laminated, and the ceramic The layer is composed mainly of a perovskite type compound (KNN compound) containing Nb and an alkali metal element, and the internal electrode contains a base metal material, and alternating electric fields having polarities that are at least twice the coercive electric field. The piezoelectric ceramic is driven by continuously applying to the piezoelectric ceramic.

  The piezoelectric ceramic driving method of the present invention is preferably bipolar driving.

  In the piezoelectric ceramic driving method of the present invention, it is preferable that the base metal material contains Ni.

  Furthermore, in the piezoelectric ceramic driving method of the present invention, the piezoelectric ceramic preferably has a coercive electric field of 1 kV / mm or less.

  In the piezoelectric ceramic driving method of the present invention, the piezoelectric ceramic preferably has an electromechanical coupling coefficient of 20% or less.

  The piezoelectric ceramic according to the present invention is a piezoelectric ceramic in which ceramic layers and internal electrodes are alternately laminated, and the ceramic layer contains a perovskite type compound (KNN compound) containing Nb and an alkali metal element. In addition to being a main component, the internal electrode contains a base metal material, and an electric field having a polarity different from that of the coercive electric field is applied alternately and continuously.

  The piezoelectric ceramic of the present invention preferably has a coercive electric field of 1 kV / mm or less.

  Furthermore, the piezoelectric ceramic of the present invention preferably has an electromechanical coupling coefficient of 20% or less.

  In the piezoelectric ceramic of the present invention, it is preferable that the base metal material contains Ni.

  According to the piezoelectric ceramic driving method and piezoelectric ceramic of the present invention, a KNN compound having a small coercive electric field and a small electromechanical coupling coefficient is used for the ceramic layer, and electric fields having polarities of two or more times the coercive electric field are alternately continuous. Therefore, it is possible to obtain a highly reliable piezoelectric ceramic having a large displacement even when continuously driven for a long time with a higher applied electric field.

It is sectional drawing which shows one Embodiment of the piezoelectric ceramic which concerns on this invention. It is a figure for demonstrating the drive method of the laminated piezoelectric actuator using the piezoelectric ceramic which concerns on this invention. It is a figure which shows an example of the electric field waveform of a unipolar drive. It is a figure which shows an example of the electric field waveform of bipolar drive. It is a hysteresis curve which shows an example of a polarization-electric field characteristic.

  Next, an embodiment of the present invention will be described in detail.

  FIG. 1 is a sectional view showing an embodiment of a piezoelectric ceramic used in the driving method according to the present invention.

  The piezoelectric ceramic 1 is formed of a sintered body in which ceramic layers 2 (2a to 2h) and internal electrodes 3 (3a to 3g) mainly composed of a base metal material are alternately stacked.

  Specifically, in the piezoelectric ceramic 1, the internal electrodes 3a, 3c, 3e, and 3g are exposed on one end face so that the internal electrodes 3 are staggered, and the internal electrodes 3b, 3d, 3f is exposed on the surface.

The ceramic layer 2 is formed with an alkali metal niobate compound (KNN compound) represented by the general formula ANbO ₃ (A: alkali metal element) as a main component.

  Here, the “main component” means a case where the piezoelectric ceramic 1 contains 50% by weight or more.

The composition of the KNN compound is not particularly limited, but is preferably a composition in which the coercive electric field Ec and the electromechanical coupling coefficient k _{31 in the} length direction are small. For example, the coercive electric field Ec is 1 kV / mm or less, A component composition system in which the mechanical coupling coefficient k ₃₁ is 20% or less can be preferably used.

  In addition, the alkali metal element in the KNN compound is not particularly limited, and an alkali metal element that is usually widely used, such as K, Na, Li, and the like can be appropriately used.

  The internal electrode 3 is not particularly limited as long as it is a base metal material, and Ni, Cu, or alloys thereof can be used, but usually Ni can be preferably used.

  FIG. 2 is a cross-sectional view of the multilayer piezoelectric actuator including the piezoelectric ceramic 1.

  That is, in this multilayer piezoelectric actuator, external electrodes 4a and 4b made of Ag, Ni-Cu, or the like are formed on both end faces of the piezoelectric ceramic 1, and an AC power supply 5 is interposed between the external electrode 4a and the external electrode 4b. Yes. When an electric field having a polarity different from that of the coercive electric field Ec by two or more times is continuously applied alternately between the external electrode 4a and the external electrode 4b, the laminated piezoelectric actuator is bipolar-driven and has an arrow due to the piezoelectric longitudinal effect. A highly reliable laminated piezoelectric actuator having a large amount of displacement can be obtained even when displaced in the laminating direction shown in the X direction and driven for a long time with a higher applied electric field.

  Next, the reason why the KNN compound is used for the ceramic layer 2 and bipolar driving is described.

  When a KNN-based compound is used for the ceramic layer 2 and a base metal material is used for the internal electrode 3, the base metal material is inferior in oxidation resistance, so that the simultaneous firing of the ceramic layer 2 and the internal electrode 3 is performed in a reducing atmosphere. There is a need to do.

  However, when a KNN compound is fired in a reducing atmosphere, oxygen defects are generated in the crystal lattice of the KNN compound. When the ceramic layer having such oxygen defects is driven unipolarly, the insulation resistance is significantly deteriorated when continuously driven for a long time. Particularly, a high electric field having a maximum electric field Emax exceeding 1 kV / mm is continuously applied for a long time. When applied, there is a risk that piezoelectric displacement will not occur.

  FIG. 3 shows an example of the electric field waveform of unipolar driving, where the horizontal axis is time t and the vertical axis is the electric field E.

  In the case of unipolar driving, as shown in FIG. 3, a sinusoidal electric field is applied to the external electrodes 4a and 4b at a predetermined frequency in the positive direction in the range of 0 to + Emax. In this case, if the driving is continued for a long time, oxygen defects move during application of an electric field, and so-called migration may occur. As a result, when the continuous driving is performed with a high electric field such that the maximum electric field Emax exceeds 1 kV / mm, the deterioration of the insulating property becomes remarkable, and there is a possibility that the piezoelectric displacement does not occur and the reliability is impaired.

  On the other hand, FIG. 4 shows an example of an electric field waveform of bipolar driving, where the horizontal axis is time t and the vertical axis is the electric field E.

  In the case of bipolar driving, as shown in FIG. 4, for example, sinusoidal electric fields having different polarities in the range of −Emax to + Emax are alternately and continuously applied. Then, it is considered that migration of oxygen defects can be suppressed by alternately and continuously applying electric fields having different polarities.

  Therefore, from the viewpoint of suppressing migration due to oxygen defects, it is necessary to drive the piezoelectric ceramic 1 in a bipolar manner.

  As a material for forming the ceramic layer 2, it is desirable to use a KNN compound in consideration of hysteresis of polarization-electrode characteristics.

  FIG. 5 is a diagram showing the polarization-electric field characteristics of the piezoelectric ceramic material. The horizontal axis is the electric field E, and the vertical axis is the polarization P. In the figure, the solid line shows the hysteresis curve of the KNN compound, and the phantom line shows the hysteresis curve of the PZT compound. Intersections between the hysteresis curves and the x-axis are coercive electric fields Ec and Ec ′ of the respective compounds.

  That is, the PZT-based compound has a large hysteresis and a large coercive electric field Ec ′ as shown by the phantom line. For this reason, when the polarity is reversed from the forward direction to the reverse direction or from the reverse direction to the forward direction, the ceramic layer 2 may be greatly strained to cause structural defects such as cracks.

On the other hand, as shown by the solid line, the KNN-based compound has a small polarization-electric field characteristic hysteresis, a small coercive electric field Ec, and a small distortion at the time of polarization reversal. In addition, since the electromechanical coupling coefficient k ₃₁ is small, a relatively high electric field can be applied without causing structural defects such as cracks even when a high electric field twice or more of the coercive electric field Ec is applied. A displacement amount can be obtained.

  As a material for forming the ceramic layer 2, a barium titanate compound (hereinafter referred to as “BT compound”) is also conceivable, but the BT compound has a small displacement in terms of material characteristics compared to the KNN compound, It is not preferable.

  Therefore, it is desirable to use the above-mentioned KNN compound as the material for forming the ceramic layer 2.

That is, in the conventional piezoelectric material, the more the coercive electric field Ec is high, it is possible to apply an electric field in the opposite direction to the high electric field, as the electromechanical coupling factor k ₃₁ is large, it is possible to increase the displacement.

However, from the viewpoint of reliability, coercive field Ec is lowered, by using the electromechanical coupling factor k ₃₁ is smaller KNN compound that is bipolar drive desirable.

As described above, in the present embodiment, by using a KNN-based compound having a small coercive electric field Ec and a small electromechanical coupling coefficient k ₃₁ for the ceramic layer 2, electric fields different in polarity by two times or more of the coercive electric field are alternately and continuously formed. Since it is driven, it is possible to obtain a piezoelectric ceramic having a large displacement without impairing reliability even when continuously driven for a long time with a high applied electric field.

  The upper limit of the driving electric field is not particularly limited, but is practically preferably ± 4 kV / mm or less in consideration of mechanical strength and the like.

  Next, a method for manufacturing the multilayer piezoelectric actuator will be described in detail.

  First, a ceramic raw material constituting a KNN-based compound such as an A compound containing an alkali metal element A and an Nb compound containing Nb is prepared. The form of the compound may be any of oxide, carbonate, and hydroxide.

Next, the ceramic raw materials are weighed in predetermined amounts so that the coercive electric field Ec of the fired piezoelectric ceramic 1 is preferably 1 kV / mm or less and the electromechanical coupling coefficient k ₃₁ is preferably 20% or less. The weighed product is put into a pulverizer such as a ball mill or pot mill containing a pulverizing medium such as PSZ (partially stabilized zirconia) balls, and sufficiently wet pulverized in a solvent such as ethanol to obtain a mixture.

  And after drying this mixture, it calcines and synthesize | combines by predetermined temperature (for example, 850-1000 degreeC), and a calcined material is obtained.

  Next, the calcined product thus obtained is crushed, and then an organic binder and a dispersant are added, and wet mixing is performed in a ball mill using pure water as a solvent to obtain a ceramic slurry. And after that, a ceramic green sheet is produced by carrying out a shaping | molding process using a doctor blade method etc.

  Next, a conductive paste for internal electrodes mainly composed of a base metal material such as Ni is used and screen-printed on a ceramic green sheet, thereby forming a conductive layer having a predetermined pattern.

  Next, after laminating the ceramic green sheets on which these conductive layers are formed, the ceramic green sheet on which the conductive layers are not formed is placed on the uppermost layer and pressed and pressure-bonded. Thus, a ceramic laminate in which conductive layers and ceramic green sheets are alternately laminated is produced. Next, the ceramic laminate is cut to a predetermined size, accommodated in an alumina sheath, subjected to binder removal treatment at a predetermined temperature (for example, 250 to 500 ° C.), and then subjected to a predetermined temperature in a reducing atmosphere. The piezoelectric ceramic 1 in which the ceramic layers 2 and the internal electrodes 3 are alternately laminated is obtained by firing at (for example, 1000 to 1160 ° C.).

  Next, a conductive paste for external electrodes made of Ag, Ni-Cu, or the like is applied to both ends of the piezoelectric ceramic 1, and is baked at a predetermined temperature (for example, 750 ° C. to 850 ° C.). Form. Thereafter, a polarization process is performed under a predetermined condition, whereby a laminated piezoelectric actuator can be manufactured. The external electrodes 4a and 4b may be formed by a thin film forming method such as a sputtering method or a vacuum vapor deposition method as long as the adhesion is good.

  Then, an AC power supply 5 is connected to the external electrodes 4a and 4b of the multilayer piezoelectric actuator formed as described above, and electric fields having different polarities more than twice the coercive electric field Ec are alternately and continuously applied to the external electrodes 4a and 4b. By applying and bipolar driving, it is possible to obtain a laminated piezoelectric actuator having a large displacement without impairing reliability even when driven continuously for a long time with a relatively high applied electric field.

  The present invention is not limited to the above embodiment. For example, in the above-described embodiment, a sinusoidal electric field is applied, but the electric field waveform is not limited to a sinusoidal wave, and may be, for example, a rectangular wave.

  Next, examples of the present invention will be specifically described.

[Preparation of sample]
An internal electrode material containing Ni as a main component and three kinds of KNN compounds having different compositions are simultaneously fired in a reducing atmosphere, and KNN piezoelectric ceramics (KNN (1), KNN (2), KNN (3) ) Was produced.

  Also, instead of the KNN compound, a BT compound compounded in a predetermined composition is used, and the internal electrode material mainly composed of Ni and the BT compound are simultaneously fired in a reducing atmosphere, and the BT piezoelectric ceramic is obtained. Produced.

  Further, an internal electrode material mainly composed of an Ag—Pd alloy and a PZT compound compounded in a predetermined composition were simultaneously fired in an air atmosphere to produce a PZT piezoelectric ceramic.

  The five types of piezoelectric ceramics produced as described above all have three layers, the thickness per layer of the ceramic layers is 35 μm, the external dimensions are 13 mm in length, 3 mm in width, and 0. It was 105 mm.

  Next, sputtering is performed on both main surfaces of the piezoelectric ceramic to form an external electrode made of a Ni—Cu alloy, and then an electric field of 3.0 kV / mm is applied for 30 minutes in an insulating oil at 80 ° C. Processed.

For such polarized treated five laminated piezoelectric ceramic was measured electromechanical coupling factor k ₃₁ in the coercive field Ec and length.

  The coercive electric field Ec was obtained from the intersection with the x axis where a polarization-electric field hysteresis curve was drawn on a cathode ray oscilloscope using the Sawyer tower method and the polarization was zero on the hysteresis curve.

  As a result, among the KNN piezoelectric ceramics, KNN (1) has a coercive electric field Ec of 0.8 kV / mm, KNN (2) has a coercive electric field Ec of 1.0 kV / mm, and KNN (3) The electric field Ec was 1.2 kV / mm. Further, the coercive electric field Ec of the BT piezoelectric ceramic was 0.8 kV / mm, and the coercive electric field Ec of the PZT piezoelectric ceramic was 0.6 kV / mm.

Further, the electromechanical coupling factor k ₃₁ is Inpi - using dance analyzer, resonant - was determined by antiresonance method.

As a result, of KNN-based piezoelectric ceramic, KNN (1) is an electromechanical coupling factor k ₃₁ is 18%, KNN (2) is an electromechanical coupling factor k ₃₁ is 20%, KNN (3) Electrical The mechanical coupling coefficient k ₃₁ was 27%. Further, the electromechanical coupling factor k ₃₁ in the BT-based piezoelectric ceramics is 15%, the electromechanical coupling factor k ₃₁ of the PZT-based piezoelectric ceramic was 38%.

[Sample evaluation]
The five types of piezoelectric ceramics were subjected to continuous drive tests under various high-temperature and high-humidity conditions with a temperature of 85 ° C. and a relative humidity of 85%, and unipolar drive and bipolar drive, respectively.

  Specifically, the unipolar drive was performed by applying a positive electric field having a maximum electric field Emax in the range of +1 kV / mm to +4 kV / mm to each piezoelectric ceramic with a sine wave having a frequency of 2 kHz.

  Bipolar driving was performed by applying electric fields (positive electric field and negative electric field) having different polarities to each piezoelectric ceramic with a frequency of 2 kHz with a maximum electric field Emax in the range of ± 1 kV / mm to ± 4 kV / mm.

  The continuous drive test was performed for 100 hours, and the displacement in the length direction after 100 hours of each sample was measured with a laser Doppler vibrometer. Then, the measured displacement was divided by the length dimension of the sample (= 13 mm), thereby obtaining the distortion rate. A sample having a distortion rate of 0.03% or more was judged as a good product.

  Table 1 shows the measurement results.

Sample Nos. 18 to 25 have a coercive electric field Ec of 0.8 kV / mm and an electromechanical coupling coefficient k ₃₁ of 15%, both of which are small, but because the ceramic layer is formed of a BT compound, it is unipolar. In both cases of driving and bipolar driving, the distortion rate was extremely low, 0.002 to 0.008%, indicating that the practicality was inferior.

  In Sample No. 26, structural defects such as cracks were observed after 100 hours, and the strain rate could not be measured. This is because the ceramic layer is formed of a PZT compound, so that the hysteresis of polarization-electric field characteristics is large, and when the bipolar drive is used, the polarity of the applied electric field is switched from the positive electric field to the negative electric field or from the negative electric field to the positive electric field. It is thought that it was greatly distorted.

  Sample No. 27 had a driving electric field of 1.0 kV / mm, which is less than twice the coercive electric field Ec, and because of unipolar driving, the strain rate was as small as 0.025%, indicating that the practicality was inferior.

  Since sample No. 28 is unipolar driven, if the driving electric field is increased to 2.0 kV / mm, the insulation is deteriorated due to the migration of Ag. Therefore, the driving is stopped after 100 hours and the distortion rate is increased. It could not be measured.

  Sample Nos. 4, 10, 14, and 15 are bipolar driven but have a driving electric field of ± 1.0 kV / mm and less than twice the coercive electric field Ec. As small as .015%, a sufficient amount of displacement could not be obtained.

  Sample Nos. 5, 11, and 16 were unipolarly driven, the driving electric field was as small as 1.0 kV / mm, and the strain rate was as small as 0.010 to 0.014%.

  Samples Nos. 6, 12, and 17 were driven by applying an electric field twice or more of the coercive electric field Ec, but were driven unipolar, and thus stopped driving after 100 hours. This is presumably because migration of oxygen defects occurred because the sample was fired in a reducing atmosphere.

  On the other hand, Sample Nos. 1-3, 7-9, and 13 are bipolar driven by applying an electric field twice or more of the coercive electric field Ec, so that a good distortion rate of 0.030 to 0.044% is obtained. Was found to be obtained.

In particular, as is clear from the comparison of sample numbers 2, 8, and 13, as the coercive electric field Ec is small and the electromechanical coupling coefficient k ₃₁ is small, the strain rate after 100 hours has increased, and the piezoelectric ceramic It has been found that the amount of displacement increases.

In Sample No. 13, the coercive electric field Ec was 1.2 kV / mm, the electromechanical coupling coefficient k ₃₁ was 27%, and the distortion rate was 0.031%, whereas in Sample Nos. 2 and 8, The coercive electric field Ec was 0.8 and 1.0 kV / mm, the electromechanical coupling coefficient k ₃₁ was 18% and 20%, and the strain rates were 0.036% and 0.039%, respectively.

As described above, by using bipolar driving using a piezoelectric ceramic having a coercive electric field Ec of 1.0 kV / mm or less and an electromechanical coupling coefficient k ₃₁ of 20% or less, an even larger amount of strain can be obtained even when driven continuously for 100 hours. It was found that a piezoelectric ceramic with good reliability could be obtained.

  By combining the KNN compound and the bipolar drive, a piezoelectric ceramic capable of obtaining reliability and a large amount of displacement during continuous drive is realized.

1 Piezoelectric ceramic 2 Ceramic layer 3 Internal electrode

Claims (9)

A piezoelectric ceramic driving method in which ceramic layers and internal electrodes are alternately laminated,
The ceramic layer is mainly composed of a perovskite type compound containing Nb and an alkali metal element,
The internal electrode contains a base metal material;
A method for driving a piezoelectric ceramic, wherein the piezoelectric ceramic is driven by alternately and continuously applying an electric field having a polarity that is twice or more that of a coercive electric field.   2. The method of driving a piezoelectric ceramic according to claim 1, wherein the driving is bipolar.   3. The piezoelectric ceramic driving method according to claim 1, wherein the base metal material contains Ni.   The piezoelectric ceramic driving method according to any one of claims 1 to 3, wherein the piezoelectric ceramic has a coercive electric field of 1 kV / mm or less.   The piezoelectric ceramic driving method according to any one of claims 1 to 4, wherein the piezoelectric ceramic has an electromechanical coupling coefficient of 20% or less. A piezoelectric ceramic in which ceramic layers and internal electrodes are alternately laminated,
The ceramic layer is mainly composed of a perovskite type compound containing Nb and an alkali metal element,
The internal electrode contains a base metal material;
A piezoelectric ceramic, wherein an electric field having a polarity different from that of a coercive electric field is applied alternately and continuously.   The piezoelectric ceramic according to claim 6, wherein a coercive electric field is 1 kV / mm or less.   The piezoelectric ceramic according to claim 6 or 7, wherein an electromechanical coupling coefficient is 20% or less.   The piezoelectric ceramic according to any one of claims 6 to 8, wherein the base metal material contains Ni.

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