JP2017160083A - Porcelain composition, piezoelectric element, vibrator, and method for manufacturing piezoelectric element - Google Patents

Abstract

In a piezoelectric element, high strength is achieved in a wide range of evaluation items including evaluation items (dielectric loss tangent, electromechanical coupling coefficients kr and kt, Curie point Tc, etc.) relating to characteristics of a driving state, and excellent strength is realized. To do. A piezoelectric ceramic composition is represented by the general formula (1) (PbmSrn) (Zr1-w-xy-zTiwFexSiyAlz) O3 (1), and 0.910 ≦ m ≦ 0.960, 0. .030 ≦ n ≦ 0.100, 0.970 ≦ m + n ≦ 1.060, 0.453 ≦ w ≦ 0.497, 0.006 ≦ x ≦ 0.017, 0 <y ≦ 0.002, 0 <z The main component is a compound satisfying ≦ 0.004. [Selection] Figure 4

Description

  The present invention relates to a porcelain composition, a piezoelectric element, a vibrator, and a method for manufacturing a piezoelectric element.

  Conventionally, lead zirconate titanate is known as a piezoelectric ceramic composition. Various improvements have been made to improve the performance of piezoelectric elements using such a piezoelectric ceramic composition. For example, a structure for improving mechanical quality factor Qm and reducing dielectric loss (dielectric loss tangent) by incorporating antimony (Sb) into lead zirconate titanate has been proposed (for example, Patent Documents 1-3). reference).

Japanese Patent Publication No. 48-12355 Japanese Patent Publication No.55-18059 JP-A-5-51222

  However, for example, in a piezoelectric element used for a piezoelectric vibrator such as an ultrasonic vibrator, in addition to the improvement of the mechanical quality factor Qm and the dielectric loss tangent, any of the characteristics such as the electromechanical coupling factors kr and kt and the Curie point Tc It is desirable to satisfy a high level. Moreover, in the piezoelectric element, in order to suppress damage during processing, it is desired to further increase the strength of the piezoelectric ceramic composition. Such a piezoelectric element satisfying a high level in a wide range of evaluation items including evaluation items (dielectric loss tangent, electromechanical coupling coefficients kr and kt, Curie point Tc, etc.) relating to the characteristics of the driving state has been sufficiently studied. Was not.

  The present invention has been made to solve the above-described problems, and can be realized as the following forms.

(1) According to one aspect of the present invention, a piezoelectric ceramic composition is provided. The piezoelectric ceramic composition of the general formula _{(1); (Pb m Sr} n) (Zr 1-w-x-y-z Ti w Fe x Si y Al z) O 3 ... (1); represented by 0.910 ≦ m ≦ 0.960, 0.030 ≦ n ≦ 0.100, 0.970 ≦ m + n ≦ 1.060, 0.453 ≦ w ≦ 0.497, 0.006 ≦ x ≦ 0.017 The main component is a compound satisfying 0 <y ≦ 0.002 and 0 <z ≦ 0.004.
According to the piezoelectric ceramic composition of this embodiment, in addition to the improvement of the mechanical quality factor Qm and the dielectric loss tangent, the piezoelectric element satisfying a high level for all of the characteristics such as the electromechanical coupling coefficients kr and kt and the Curie point Tc. It is possible to obtain a balanced piezoelectric characteristic that has not been obtained in the past. Moreover, the strength of the piezoelectric ceramic composition can be increased.

(2) In the piezoelectric ceramic composition of the above aspect, the dielectric loss tangent when an electric field of 1 V / mm is applied may be 0.30% or less. With such a configuration, when a piezoelectric vibrator is manufactured using the piezoelectric ceramic composition, the loss of electrical energy lost as thermal energy during operation can be suppressed, and the effect of suppressing heat generation can be enhanced. .

(3) According to another aspect of the present invention, a piezoelectric element is provided. A piezoelectric element includes the piezoelectric ceramic composition according to the above (1) or (2) and at least a pair of electrodes provided in contact with the piezoelectric ceramic composition. With such a configuration, in addition to the improvement of the mechanical quality factor Qm and the dielectric loss tangent, the electromechanical coupling factors kr and kt, the properties such as the Curie point Tc, etc. all satisfy a high level and have excellent strength. A piezoelectric element can be obtained.

(4) According to another aspect of the present invention, an ultrasonic transducer is provided. The ultrasonic transducer includes the piezoelectric element described in (3) above. With such a configuration, it is possible to improve the piezoelectric performance of the ultrasonic transducer and to use it stably for a long time by suppressing power generation.

(5) According to the other form of this invention, the manufacturing method of the piezoelectric ceramic composition as described in said (1) or (2) is provided. The method for producing a piezoelectric ceramic composition includes a mixing step of mixing raw materials of the main component to obtain a raw material mixed powder; a calcining step of calcining the raw material mixed powder to obtain a calcined powder; and the calcined powder The mixing step is performed by a ball mill using a ball substantially free of aluminum (Al). With such a configuration, in the mixing step, the content ratio of Al in the raw material mixed powder does not increase due to Al contained in the ball, and the mixing ratio when mixing the raw materials is accurate, The composition of the piezoelectric ceramic composition can be adjusted.

(6) According to another aspect of the present invention, there is provided a method for manufacturing a piezoelectric element according to (3) above. The piezoelectric element manufacturing method includes a mixing step of mixing raw materials of the main component to obtain a raw material mixed powder; a calcining step of calcining the raw material mixed powder to obtain a calcined powder; and molding the calcined powder And firing to obtain a piezoelectric ceramic composition; and a coating process for applying a conductive paste for forming the electrode on the surface of the piezoelectric ceramic composition; It is characterized by containing substantially no silicon (Si). With such a configuration, due to Si contained in the conductive paste, the content ratio of Si in the piezoelectric ceramic composition included in the piezoelectric element does not increase, depending on the mixing ratio when mixing the raw materials, The composition of the piezoelectric ceramic composition can be adjusted with high accuracy.

  The present invention can be realized in various forms. For example, a piezoelectric ceramic composition, a piezoelectric element using the composition, and various devices including a piezoelectric element (a knock sensor, an ultrasonic vibrator, a cutting tool, an ultrasonic (Sound wave sensor, actuator, etc.) and a method of manufacturing a piezoelectric ceramic composition.

The flowchart which shows the manufacturing method of the piezoelectric ceramic composition in one Embodiment of this invention. The perspective view which shows the piezoelectric element as one Embodiment of this invention. 1 is a longitudinal sectional view showing an ultrasonic transducer as one embodiment of the present invention. The figure which shows the experimental result regarding the influence on the piezoelectric characteristic of the composition of a porcelain composition. The figure which shows the influence on the dielectric loss tangent of the coefficient y and z. The figure which shows the result of having measured the temperature change of the ultrasonic vibrator with time. The figure which shows the influence on the dielectric loss tangent of the coefficient x. Shows the relative dielectric constant in the temperature range (ε ₃₃ ^T / ε ₀₎ of 0 ° C. to 350 ° C..

A. Piezoelectric ceramic composition:
The piezoelectric ceramic composition as one embodiment of the present invention contains a compound represented by the following general formula (1), that is, a perovskite complex oxide as a main component.

_{(Pb m Sr n) (Zr} 1-w-x-y-z Ti w Fe x Si y Al z) O 3 ... (1)

Here, the piezoelectric ceramic composition of the present embodiment satisfies the following in the general formula (1).
0.910 ≦ m ≦ 0.960,
0.030 ≦ n ≦ 0.100,
0.970 ≦ m + n ≦ 1.060,
0.453 ≦ w ≦ 0.497,
0.006 ≦ x ≦ 0.017,
0 <y ≦ 0.002, 0 <z ≦ 0.004.

  The compound represented by the general formula (1) has lead (Pb) and strontium (Sr) at the A site of the perovskite structure. The coefficients m and n in the general formula (1) represent the ratio of Pb and Sr existing at the A site. With respect to m + n, when all of the piezoelectric ceramic composition having the above composition is composed of a perovskite phase, theoretically, m + n = 1. However, depending on the ratio of each element contained in the perovskite oxide, the ambient temperature, or the atmosphere, the amount of the A-site element, the B-site element, and the oxygen atom may deviate from the stoichiometric composition. Therefore, in this embodiment, it is defined as 0.970 ≦ m + n ≦ 1.060.

  In the general formula (1), when the coefficient m and the coefficient n are out of the ranges of 0.910 ≦ m ≦ 0.960 and 0.030 ≦ n ≦ 0.100, sufficient piezoelectric performance is obtained. It may be difficult to do. Specifically, for example, when the coefficient m is below the above range, the values of the electromechanical coupling coefficients kr and kt may be small values of 40% or less, respectively. From the viewpoint of increasing the values of the electromechanical coupling coefficients kr and kt, the coefficient m is preferably 0.920 or more. Further, from the viewpoint of increasing the values of the electromechanical coupling coefficients kr and kt, the coefficient m is preferably less than 0.950, and more preferably less than 0.930.

  The compound represented by the general formula (1) includes zirconium (Zr), titanium (Ti), iron (Fe), silicon (Si), and aluminum (Al) at the B site having a perovskite structure. The coefficients w, x, y, and z in the general formula (1) are the respective contents of Ti, Fe, Si, and Al when the total number of moles of elements existing at the B site is 1, respectively. Represents molar ratio. When the coefficients w, x, y, and z are out of the above-described ranges, it may be difficult to obtain sufficient piezoelectric performance.

  When the value of the coefficient w is out of the range of 0.453 ≦ w ≦ 0.497, there is a possibility that the mechanical quality factor Qm cannot be sufficiently secured. From the viewpoint of securing a larger value of the mechanical quality factor Qm, w is preferably 0.472 or more. Further, from the viewpoint of securing a larger value of the mechanical quality factor Qm, w is preferably 0.474 or less.

  If the value of the coefficient x is below the range of 0.006 ≦ x ≦ 0.017, the dielectric loss may be increased to an unacceptable level. Specifically, for example, the dielectric loss tangent when an electric field of 1 V / mm is applied may exceed 0.30%, or the dielectric loss tangent when an electric field of 200 V / mm is applied may exceed 0.40%. Furthermore, when the coefficient x is smaller than the above range, the value of the mechanical quality factor Qm may be a small value less than 1000. When the coefficient x is larger than the above range, the insulation is partially reduced because the Fe content in the piezoelectric ceramic composition is increased, so that the polarization described later in the manufacturing process of the piezoelectric ceramic composition is performed. Leakage current flows during processing, which can damage the piezoelectric ceramic composition.

  When the values of the coefficient y and the coefficient z are below the above range, that is, when the piezoelectric ceramic composition of the present embodiment does not contain Si and Al, there is a possibility that the strength of the piezoelectric ceramic composition cannot be sufficiently secured. In addition, there is a possibility that the composition of the piezoelectric ceramic composition cannot be made sufficiently uniform. By increasing the strength of the piezoelectric ceramic composition, for example, damage to the piezoelectric ceramic composition, specifically chipping (chipping) or the like in the processing step during the production of the piezoelectric ceramic composition can be suppressed. From the viewpoint of sufficiently ensuring the strength of the piezoelectric ceramic composition, it is preferable to satisfy 0.001 ≦ y and 0.001 ≦ z.

  When the value of the coefficient y exceeds the range of 0 <y ≦ 0.002, or when the value of the coefficient z exceeds the range of 0 <z ≦ 0.004, the composition of the piezoelectric ceramic composition is sufficiently uniform. There is a possibility that the crystallinity cannot be sufficiently increased. Also, when the value of the coefficient y exceeds the range of 0 <y ≦ 0.002, or when the value of the coefficient z exceeds the range of 0 <z ≦ 0.004, the dielectric loss is unacceptably large. There is a possibility. For example, the dielectric loss tangent when an electric field of 1 V / mm is applied may exceed 0.30%, or the dielectric loss tangent when an electric field of 200 V / mm is applied may exceed 0.40%. From the viewpoint of sufficiently reducing the dielectric loss tangent, z ≦ 0.003 is preferable. By keeping the values of the coefficients y and z within the above ranges and suppressing the dielectric loss to a low level, when a piezoelectric vibrator, for example, an ultrasonic vibrator is manufactured using the piezoelectric ceramic composition, heat generated during the operation of the piezoelectric vibrator is generated. Can be suppressed. Since the heat generation during operation can be suppressed, the piezoelectric vibrator can be used stably for a long time, the input power limit can be suppressed, and the cooling device can be reduced or eliminated.

  According to the piezoelectric ceramic composition of the present embodiment configured as described above, in addition to the improvement of the mechanical quality factor Qm and the dielectric loss tangent, by setting each coefficient in the general formula (1) to the range described above. In addition, a piezoelectric ceramic composition satisfying a high level of any of the characteristics such as the electromechanical coupling coefficients kr and kt and the Curie point Tc can be obtained. That is, it is possible to obtain a piezoelectric element that satisfies a high level in a wide range of evaluation items including evaluation items related to the characteristics of the driving state. Specifically, the dielectric loss tangent when an electric field of 1 V / mm is applied is 0.30% or less, the dielectric loss tangent when an electric field of 200 V / mm is applied is 0.40% or less, and the mechanical quality factor Qm is 1000 or more. The electromechanical coupling coefficients kr and Kt exceed 40%, and the Curie point Tc can be set to 300 ° C. or higher. As a result, it is possible to realize a well-balanced piezoelectric characteristic that has not been obtained conventionally. In addition, by setting each coefficient in the general formula (1) within the range described above, the strength of the piezoelectric ceramic composition can be increased and damage to the piezoelectric ceramic composition can be suppressed. Alternatively, the yield when manufacturing the piezoelectric element can be increased. The “dielectric loss tangent” in the present specification refers to the dielectric loss tangent at a frequency of 1 kHz.

  In the piezoelectric ceramic composition of the present embodiment, by controlling each coefficient in the general formula (1), characteristic values such as dielectric loss tangent, mechanical quality factor Qm, electromechanical coupling factors kr and Kt, and Curie point Tc are changed. can do. Each coefficient when the main component of the piezoelectric ceramic composition of the present embodiment is represented by the general formula (1) can be adjusted by, for example, the blending ratio of the raw materials at the time of manufacturing the piezoelectric ceramic composition. A method for producing the piezoelectric ceramic composition will be described later. Moreover, each coefficient when the main component of the piezoelectric ceramic composition of the present embodiment is represented by the general formula (1) can be obtained by performing ICP emission spectroscopic analysis on the piezoelectric ceramic composition. When the element to be measured in the sample is 1000 ppm or more, the ICP-AES method (ICP emission spectroscopy) may be used, and when it is less than 1000 ppm, the ICP-MS method (ICP mass spectrometry) may be used. .

In addition, the piezoelectric ceramic composition of the present embodiment can contain components other than the main component as long as the object of the present invention is not impaired. As other components, lead stannate (Pb ₂ SnO ₄ ), cobalt oxide (CoO), nickel oxide (NiO), lead cobalt niobate (Pb (Co _1/3 Nb _2/3 ) O ₃ ), nickel niobium Lead acid (Pb (Ni _1/3 Nb _2/3 ) O ₃ ), lead magnesium niobate (Pb (Mg _1/3 Nb _2/3 ) O ₃ ), and the like can be given. Only 1 type may contain these and 2 or more types may contain. In addition, it is preferable that content of these other components shall be less than 10 mol% with respect to the whole piezoelectric ceramic composition.

B. Production method of piezoelectric element:
FIG. 1 is a flowchart showing a method for manufacturing a piezoelectric element including the piezoelectric ceramic composition of the present embodiment described above. In this embodiment, the piezoelectric ceramic composition is formed by a solid phase reaction method. The solid-phase reaction method is a method in which a raw material powder that is a compound containing a constituent metal element such as an oxide, carbonate, or nitrate is formed according to the composition of the oxide to be produced. This is a well-known method of synthesizing a desired oxide by weighing and mixing so as to obtain a ratio, followed by heat treatment (firing).

When manufacturing a piezoelectric ceramic composition, first, raw material powder is weighed and mixed (step T110). Examples of the raw material powder include lead oxide (PbO), zirconium oxide (ZrO ₂ ), titanium oxide (TiO ₂ ), strontium oxide (SrCO ₃ ), iron oxide (Fe ₂ O ₃ ), silicon dioxide (SiO ₂ ), Alternatively, aluminum oxide (Al ₂ O ₃ ) can be used. These raw material powders are weighed according to the value of each coefficient in the general formula (1). Then, ethanol is added to these raw material powders, wet mixing and pulverization using a ball mill are performed, and the raw material mixed powder is obtained after drying. This step T110 corresponds to a “mixing step”.

  Thereafter, the obtained raw material mixed powder is calcined and pulverized to obtain a calcined powder (step T120). The calcination can be performed, for example, at 800 ° C. for 2 to 3 hours in an air atmosphere. The average particle diameter of the calcined powder can be set to 0.6 to 2.0 μm, for example. This process T120 corresponds to a “calcination process”.

  After calcination, a granulated powder is produced from the calcined powder, and the obtained granulated powder is molded to obtain a molded body (step T130). Specifically, in step T130, for example, after adding a binder and ethanol to the calcined powder, wet mixing and pulverization are performed, and a granulated powder is obtained after drying. And the obtained granulated powder is shape | molded by the uniaxial press to the shape of a desired piezoelectric ceramic composition. The shape of the piezoelectric ceramic composition can be, for example, a disk shape, a columnar shape, a rectangular flat plate shape, or the like. After molding, for example, CIP processing (cold isostatic pressing) is performed at a pressure of 150 MPa to obtain a molded body.

  Thereafter, the obtained molded body is fired at a firing temperature higher than the calcining temperature to obtain a piezoelectric ceramic composition (step T140). Firing can be performed, for example, at 1000 to 1400 ° C. for 2 to 4 hours in an air atmosphere. Prior to firing, degreasing (decomposition by heating of an organic substance such as a binder) may be performed. This process T140 corresponds to a “firing process”.

  After firing, the obtained fired body is processed according to the required dimensional accuracy to complete a piezoelectric body made of a piezoelectric ceramic composition (step T150). The processing may be performed by, for example, surface polishing.

  Thereafter, an electrode is attached by applying and baking a conductive paste on the surface of the obtained piezoelectric body (step T160). The conductive paste can be a silver paste, for example, and the conductive paste can be applied by, for example, screen printing. This step T160 includes an “application step”.

  After electrode formation, polarization processing is performed (step T170) to complete the piezoelectric element. The polarization treatment is a treatment for expressing the piezoelectric characteristics in the fired body. For example, a DC electric field of 3 to 5 kV / mm is applied to the piezoelectric body on which the electrode is formed in silicone oil at 100 to 150 ° C. Can be done.

In addition, when wet mixing the raw material powder using a ball mill in step T110, for example, when using a ball containing aluminum (Al), the piezoelectric ceramic composition may contain aluminum derived from the ball. is there. In such a case, the aluminum content in the piezoelectric ceramic composition obtained after step T140 should satisfy the range of the coefficient z described with respect to the general formula (1). In order to accurately control the aluminum content in the piezoelectric ceramic composition by the mixing ratio of the raw material powder in the process T110, the ball used when performing ball mill mixing in the process T110 may contain substantially no aluminum. For example, it is desirable to use a resin ball or a zirconium oxide (ZrO ₂ ) ball. The phrase “the ball does not substantially contain aluminum” means that the aluminum content in the ball is 1.0 wt% or less.

  Further, when the conductive paste used to form the electrode in step T160 includes a glass component containing silicon (Si), the piezoelectric ceramic composition may contain silicon derived from the conductive paste. There is. In such a case, the silicon content in the piezoelectric ceramic composition after step T160 may satisfy the range of the coefficient y described with respect to the general formula (1). In order to accurately control the content ratio of silicon in the piezoelectric ceramic composition by the mixing ratio of the raw material powder in step T110, it is desirable that the conductive paste used in step T160 substantially does not contain silicon. In addition, that a conductive paste does not contain silicon substantially means that the content rate of the silicon in a conductive paste is 1.0 wt% or less.

C. Piezoelectric element:
FIG. 2 is a perspective view showing an example of a piezoelectric element manufactured according to the manufacturing method of FIG. The piezoelectric element 200 has a configuration in which a pair of electrodes 301 and 302 are attached to the upper and lower surfaces of a disk-shaped piezoelectric body 100 that is a piezoelectric ceramic composition of this embodiment manufactured according to steps T110 to T150. doing.

  In the embodiment of the present invention, the piezoelectric element only needs to include a piezoelectric body composed of the piezoelectric ceramic composition described above and at least a pair of electrodes provided in contact with the piezoelectric body. The piezoelectric body can have various shapes other than those shown in FIG. The shape of the piezoelectric body may be various shapes such as a columnar shape, a prismatic shape, or a columnar shape in which a through hole is provided in the thickness direction in the central portion. The piezoelectric element may be configured by laminating a plurality of piezoelectric bodies having these shapes.

  The “pair of electrodes” is a conductor layer formed on the surface of the piezoelectric body. The electrodes are formed on the upper and lower surfaces of the piezoelectric body, and each electrode may be formed on the same surface of the piezoelectric body. In addition, the shape, size, material, and the like of the electrode are not particularly limited, and can be appropriately determined depending on the size, use, etc. of the piezoelectric body. The shape of this electrode may be flat, and for example, when each of the pair of electrodes is formed on the same surface of the piezoelectric body, it may be comb-like.

D. Ultrasonic transducer:
FIG. 3 is a longitudinal sectional view showing an ultrasonic transducer as one embodiment of the present invention. The ultrasonic transducer 20 is a Langevin type ultrasonic transducer and includes a piezoelectric element 22 and a pair of upper and lower front plates 25 and a backing plate 26 that sandwich the piezoelectric element 22. The piezoelectric element 22 includes two piezoelectric bodies 23a and 23b formed in an annular shape with an electrode plate 24a interposed therebetween, and an electrode plate 24b disposed above the upper piezoelectric body 23b. It is configured. The piezoelectric bodies 23a and 23b are composed of the piezoelectric ceramic composition of the present embodiment. The front plate 25 and the backing plate 26 are made of cylindrical metal blocks formed using iron or aluminum as a material. And the piezoelectric element 22 is arrange | positioned between this front board 25 and the backing board 26, and these are integrally couple | bonded by the center volt | bolt 27. FIG.

  The front plate 25 and the backing plate 26 are both formed larger in diameter than the piezoelectric bodies 23 a and 23 b, and the contact ends with the piezoelectric bodies 23 a and 23 b are reduced in diameter via the conical portions 28 and 29. Thus, the diameters of the piezoelectric bodies 23a and 23b are substantially equal. The diameter of the cross section of the backing plate 26 and the diameter of the cross section of the front plate 25 are provided with substantially the same dimensions, and the outer end surface of the front plate 25 is an ultrasonic radiation surface 30. The backing plate 26 is formed with a blind end hole 31 having a circular cross section extending from the center of the outer end surface of the backing plate 26 toward the front plate 25 along the axial direction. And the full length of the ultrasonic transducer | vibrator 20 which consists of this structure is set so that it may correspond substantially to the resonant length of 3/2 wavelength of a predetermined resonant frequency.

  This ultrasonic vibrator includes a piezoelectric element constituted by the piezoelectric ceramic composition of the present embodiment having excellent piezoelectric characteristics. That is, the piezoelectric ceramic composition constituting the piezoelectric element of the ultrasonic vibrator has a dielectric loss tangent of 0.30% or less when an electric field of 1 V / mm is applied and a dielectric loss tangent of 0.2 when an electric field of 200 V / mm is applied. A piezoelectric ceramic composition having a mechanical quality factor Qm of 1000 or more, an electromechanical coupling coefficient kr and Kt of more than 40%, and a Curie point Tc of 300 ° C. or more can be used. By using a piezoelectric element having excellent piezoelectric performance in this way, it is possible to generate ultrasonic waves at a stable frequency. In addition, since the piezoelectric element having excellent strength is used and heat generation during operation can be suppressed, an ultrasonic vibrator having excellent thermal durability can be realized. Although the ultrasonic transducer of FIG. 3 includes the two piezoelectric bodies 23a and 23b, it may have a different configuration. For example, the number of piezoelectric bodies included in the ultrasonic transducer can be set to an arbitrary number of three or more.

E. Variations:
In the above-described embodiment, an ultrasonic vibrator is shown as a piezoelectric element. However, it may have a different configuration, and can be widely used for vibration detection applications, pressure detection applications, oscillation applications, piezoelectric device applications, and the like. The piezoelectric element of the embodiment can be applied to, for example, an ultrasonic motor or an ultrasonic scalpel that is another piezoelectric vibrator, or sensors (non-resonant knocking sensor, combustion pressure sensor, etc.) that detect various vibrations ), Actuators, high-voltage generators, various drive devices, position control devices, vibration suppression devices, fluid discharge devices (paint discharge, fuel discharge, etc.), and the like.

FIG. 4 is a diagram showing experimental results regarding the influence of the composition of each sample on the piezoelectric characteristics of 18 types of piezoelectric elements from sample S01 to sample S18. Here, samples S01 to S03, S06 to S08, S11 to S14 are examples, and samples S04, S05, S09, S10, and S15 to S18 are comparative examples. In FIG. 4, relative permittivity ε ₃₃ ^T / ε ₀ , dielectric loss tangent (tan δ), electromechanical coupling coefficient kr for radial vibration, electromechanical coupling coefficient kt for thickness vibration, and mechanical quality factor for each sample. Qm, piezoelectric d constant d ₃₃ , and Curie point Tc are shown.

<Production of each sample>
The piezoelectric element of each sample was produced according to the above-described steps T110 to T170 in FIG. The ratio of each element shown in FIG. 4 is obtained by actually measuring the ratio of each element contained in the fired piezoelectric element. In Step T130, a disk-shaped molded body having a diameter of 19.0 mm and a thickness of 1.4 mm was obtained by uniaxial pressing of the granulated powder. However, the sample for obtaining the dielectric loss tangent was a disk having a diameter of 14.0 mm and a thickness of 1.0 mm. The shape of the piezoelectric body used in the vibrator for measuring the temperature rise during operation will be described later. In addition, after the polarization process of process T170, the obtained piezoelectric element was heat-processed at 100 degreeC for 5 hours, and various characteristics evaluation was performed after 24 hours progress. The evaluation method is as follows.

<Relative permittivity (ε ₃₃ ^T / ε ₀ )>
The measurement was performed using an impedance analyzer (HP4194A type, manufactured by Hewlett-Packard Company) at room temperature, and the value was calculated from the capacitance value at 1 kHz. Among samples S01 to S18, samples S01 and S04 were measured for relative dielectric constant (ε ₃₃ ^T / ε ₀ ) even under conditions where the temperature was changed from 0 ° C. to 350 ° C.

<Dielectric loss tangent tan δ>
The dielectric loss tangent, which is an index of dielectric loss, was measured using an impedance analyzer (HP4194A type, manufactured by Hewlett-Packard Company) at room temperature, and calculated from the capacitance value at a frequency of 1 kHz. Specifically, the evaluation was performed according to European standard BS EN 50324-3: 2002 “Method of measurement High power”. As dielectric loss, a dielectric loss tangent (tan δ (1 V / mm)) when an electric field of 1 V / mm was applied and a dielectric loss tangent (tan δ (200 V / mm)) when an electric field of 200 V / mm was applied were determined.

<Curie point Tc>
Measurement was performed using the impedance analyzer while heating each sample in an electric furnace, and the temperature was determined as the temperature at which piezoelectricity disappeared and Δf (= fp−fs) = 0. Note that fp represents the series resonance frequency in the equivalent circuit of the piezoelectric element, and fs represents the parallel resonance frequency.

<Piezoelectric properties _{(kr, kt, Qm, d} 33)>
The electromechanical coupling coefficient kr for radial vibration, the electromechanical coupling coefficient kt for thickness vibration, the mechanical quality factor Qm, and the piezoelectric d constant d ₃₃ are standards of the Japan Electronics and Information Technology Industries Association (JEITA: Standard of Japan Electronics and Information). Technology Industries Association) Standard No. EM-4501, “Electrical Test Method for Piezoelectric Ceramic Vibrator”.

<Bending strength>
As for the bending strength, a three-point bending strength was measured by a method based on “JIS R 1601”.

<Measurement of temperature rise of vibrator>
Using the piezoelectric elements of samples S01, S03, and S04, ultrasonic transducers similar to those shown in FIG. 3 were produced, and temperature changes over time were measured when a voltage was applied to these ultrasonic transducers. did. The ultrasonic transducer of each sample was manufactured using six ring-shaped piezoelectric bodies each having an outer diameter of 11.0 mm, an inner diameter of 6.0 mm, and a thickness of 2.0 mm. The voltage applied to the ultrasonic transducer was fixed at a frequency of 55 kHz and an amplitude of 15 μm. The vibration speed is 715 mm / sec. Met. The temperature of the piezoelectric element during vibration was measured using an INFRARED THERMOMETER AD-5611A (manufactured by A & D Co., Ltd.).

  All of the samples S01 to S03, S06 to S08, and S11 to S14 in FIG. 4 satisfy the above-described relationship relating to each coefficient in the general formula (1). These samples have a dielectric loss tangent of 0.30% or less when an electric field of 1 V / mm is applied and a dielectric loss tangent of 0.40% or less when an electric field of 200 V / mm is applied (in this embodiment, 0.30%). The mechanical quality factor Qm was 1000 or more, the electromechanical coupling coefficients kr and Kt exceeded 40%, and the Curie point Tc was 300 ° C. or more. That is, it is confirmed that by satisfying the above-described relationship relating to each coefficient in the general formula (1), a piezoelectric element satisfying a high level can be obtained in a wide range of evaluation items including evaluation items related to the characteristics of the driving state. It was.

On the other hand, in the sample S05 in which the coefficient m related to the molar ratio of Pb at the A site of the perovskite structure is out of the range of 0.910 ≦ m ≦ 0.960 and less than 0.910, the electromechanical coupling coefficient The values of kr and kt were small values of 40% or less, respectively. Further, the sample S05, the value of the piezoelectric d constant _{d 33,} was a small value below 180 (pC / N).

  In samples S09 and S10 in which the coefficient x relating to the molar ratio of Fe at the B site of the perovskite structure is out of the range of 0.006 ≦ x ≦ 0.017 and less than 0.006, when an electric field of 1 V / mm is applied And the mechanical quality factor Qm was a small value of less than 1000. Further, in sample S15 in which the coefficient x exceeds 0.017, the sample was damaged when the polarization process in step T170 of FIG. 1 was performed. This is presumably because the insulation in the piezoelectric ceramic composition was partially lowered due to the large Fe content, and a leakage current flowed during the polarization treatment (“Polarization NG” is shown in the remarks column of FIG. 4). Described). The damaged sample S15 is not evaluated for piezoelectric characteristics.

  In samples S04 and S09 in which the coefficient y related to the Si molar ratio at the B site of the perovskite structure is out of the range of 0 <y ≦ 0.002 and exceeds 0.002, the dielectric loss tangent when an electric field of 1 V / mm is applied Was greater than 0.30%.

  In the sample S04 in which the coefficient z relating to the molar ratio of Al at the B site of the perovskite structure is out of the range of 0 <z ≦ 0.004 and exceeds 0.004, the dielectric loss tangent when an electric field of 1 V / mm is applied is 0. The value was larger than 30%.

  Sample S01 and samples S16 to S18 have substantially the same coefficient values other than coefficients y and z. Specifically, in the sample S01, both the coefficient y and the coefficient z are 0.001, in the sample S16, the coefficient y is 0.001 and the coefficient z is 0, and in the sample S17, the coefficient y is 0 and the coefficient z is 0.001, and in the sample S18, the coefficient y and the coefficient z are both 0. When these samples were compared, Samples S16 to S18 had inferior bending strength and a small value of less than 100 MPa compared to Sample S01. Furthermore, due to the inferior strength, the samples S16 to S18 were chipped in the polishing step of step T150 in FIG. 1 (see the remarks column in FIG. 4). From these results, it was confirmed that the strength of the piezoelectric ceramic composition is increased by containing Si and Al in such a ratio that both the coefficient y and the coefficient z are 0.001 or more.

  Here, among the samples of the example satisfying 0.910 ≦ m ≦ 0.960, when the samples S06 to S08 having substantially the same coefficients other than m are compared, the sample S08 in which m = 0.920 is obtained. Compared with sample S06 where m = 0.910 and sample S07 where m = 0.930, both electromechanical coupling coefficients kr and kt were higher. For this reason, it is considered that the values of the electromechanical coupling coefficients kr and kt can be further increased by setting m to 0.920 or more, or setting m to less than 0.93.

  Among the samples of the example satisfying 0.453 ≦ w ≦ 0.497, the samples S01 to S03 satisfying 0.472 ≦ w ≦ 0.474 have a larger mechanical quality factor Qm of 1600 kr or more. Indicated. Therefore, it is considered that the value of the mechanical quality factor Qm can be further increased by setting w to 0.472 or more or setting w to 0.474 or less.

  FIG. 5 is a diagram collectively showing the results of measuring the dielectric loss tangent of representative samples S01 to S04 when an electric field of 1 V / mm is applied and when an electric field of 200 V / mm is applied. Samples S01 to S04 are different from each other in the coefficient of the general formula (1) in that the coefficient y related to the molar ratio of Si and the coefficient z related to the molar ratio of Al are different from each other. The molar ratio (content ratio) is increasing. As shown in FIG. 5, the greater the Si and Al content ratio, the greater the value of dielectric loss tangent (dielectric loss tangent at a frequency of 1 kHz). In particular, when the content ratio of Si and Al exceeds the conditions of sample S03, that is, when the coefficient y exceeds 0.002 and the coefficient z exceeds 0.004, the value of the dielectric loss tangent increases rapidly. . Therefore, by setting the content ratio of Si and Al to be equal to or less than the conditions of the sample S03, that is, the coefficient y is 0.002 or less and the coefficient z is 0.004 or less, the value of dielectric loss tangent As a result, it was confirmed that a low value was stably obtained. Specifically, the dielectric loss tangent when an electric field of 1 V / mm is applied is 0.24%, which is 0.30% or less, and the dielectric loss tangent when an electric field of 200 V / mm is applied is 0.40% or less. Realized. In each sample, the dielectric loss tangent was larger when an electric field of 200 V / mm was applied than when an electric field of 1 V / mm was applied.

  FIG. 6 is a diagram showing the results of measuring the temperature change during operation by fabricating an ultrasonic transducer using representative samples S01, S03, and S04. As shown in FIG. 6, in samples S01 and S03, the piezoelectric element temperature was stable at 40 ° C. or lower even when the continuous use time exceeded 600 hours. On the other hand, Sample S04 became unusable due to thermal runaway and a rapid temperature rise. As described above, by setting the coefficient y to 0.002 or less and the coefficient z to 0.004 or less, a stable low value can be obtained as the value of the dielectric loss tangent. In this way, the value of the dielectric loss tangent of the piezoelectric element is as low as 0.30% or less when a 1 V / mm electric field is applied, or 0.40% or less when a 200 V / mm electric field is applied. By setting the value, it was confirmed that the temperature rise during operation of the ultrasonic vibrator incorporating the piezoelectric element was suppressed, and the effect of enabling long-term stable use was obtained.

  FIG. 7 is a graph showing the relationship between the results of measuring the dielectric loss tangent of a representative sample S01, S09 to S14 when an electric field of 1 V / mm is applied, and the Fe content. In particular, S10 to S14 are common in that the coefficient y related to the molar ratio of Si and the coefficient z related to the molar ratio of Al are both 0.002. In FIG. 7, the coefficient x related to the Fe molar ratio is taken on the horizontal axis, and the dielectric loss tangent tan δ is taken on the vertical axis, so that the influence of the Fe content in the piezoelectric ceramic composition on the dielectric loss tangent is shown. From FIG. 7, by setting the value of the coefficient x related to the molar ratio of Fe within the range of 0.006 ≦ x ≦ 0.017, the dielectric loss tangent when an electric field of 1 V / mm is applied is as low as 0.28% or less. It was confirmed that From the above, it can be said that the dielectric loss tangent is further influenced by the Fe content (x) in addition to the Si content (y) and the Al content (z). From the comparison between the samples S01 and S13 in FIG. 7, if the coefficient x related to the molar ratio of Fe is the same, the coefficient y related to the molar ratio of Si and the coefficient z related to the molar ratio of Al are both It can be seen that the dielectric loss tangent can be further reduced by setting the value to 0.001 smaller than that.

FIG. 8 is a diagram showing the results of measuring the relative permittivity (ε ₃₃ ^T / ε ₀ ) in a temperature range of 0 ° C. to 350 ° C. for representative samples S01 and S04. When these samples were compared, there was a difference in the rate of change of the relative dielectric constant in the vicinity of the Curie temperature (Curie point Tc) at which the relative dielectric constant exhibited a peak. That is, the half width of sample S01 was about 30 ° C., and the half width of sample S04 was about 60 ° C. From the above results, it is considered that the piezoelectric ceramic composition of sample S01 is composed of a more uniform composition and crystal than sample S04, and therefore the dielectric loss tangent is smaller.

  The present invention is not limited to the above-described embodiments, examples, and modifications, and can be realized with various configurations without departing from the spirit thereof. For example, the technical features in the embodiments, examples, and modifications corresponding to the technical features in each embodiment described in the summary section of the invention are to solve some or all of the above-described problems, or In order to achieve part or all of the above effects, replacement or combination can be performed as appropriate. Further, if the technical feature is not described as essential in the present specification, it can be deleted as appropriate.

DESCRIPTION OF SYMBOLS 20 ... Ultrasonic vibrator 22 ... Piezoelectric element 23a, 23b ... Piezoelectric body 24a, 24b ... Electrode plate 25 ... Front plate 26 ... Backing plate 27 ... Center bolt 28, 29 ... Conical part 30 ... Ultrasonic radiation surface 31 ... Blind end Hole 100 ... piezoelectric body 200 ... piezoelectric element 301, 302 ... electrode

Claims (6)

A piezoelectric ceramic composition comprising:
General formula (1)
_{(Pb m Sr n) (Zr} 1-w-x-y-z Ti w Fe x Si y Al z) O 3 ... (1)
Represented by
0.910 ≦ m ≦ 0.960,
0.030 ≦ n ≦ 0.100,
0.970 ≦ m + n ≦ 1.060,
0.453 ≦ w ≦ 0.497,
0.006 ≦ x ≦ 0.017,
0 <y ≦ 0.002, 0 <z ≦ 0.004
A piezoelectric ceramic composition comprising a compound satisfying the above requirements as a main component. The piezoelectric ceramic composition according to claim 1,
A piezoelectric ceramic composition having a dielectric loss tangent of 0.30% or less when an electric field of 1 V / mm is applied. A piezoelectric element,
A piezoelectric element comprising: the piezoelectric ceramic composition according to claim 1 or 2; and at least a pair of electrodes provided in contact with the piezoelectric ceramic composition.   An ultrasonic transducer comprising the piezoelectric element according to claim 3. It is a manufacturing method of the piezoelectric ceramic composition according to claim 1 or 2,
A mixing step of mixing the raw materials of the main component to obtain a raw material mixed powder;
A calcining step of calcining the raw material mixed powder to obtain a calcined powder;
A calcining step of forming and calcining the calcined powder;
With
The method for producing a piezoelectric ceramic composition, wherein the mixing step is performed by a ball mill using a ball substantially free of aluminum (Al). It is a manufacturing method of the piezoelectric element according to claim 3,
A mixing step of mixing the raw materials of the main component to obtain a raw material mixed powder;
A calcining step of calcining the raw material mixed powder to obtain a calcined powder;
A calcining step of forming and calcining the calcined powder to obtain a piezoelectric ceramic composition;
An application step of applying a conductive paste for forming the electrode on the surface of the piezoelectric ceramic composition;
With
The method for manufacturing a piezoelectric element, wherein the conductive paste contains substantially no silicon (Si).

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