Piezoelectric ceramics, piezoelectric elements and ultrasonic transducers

Abstract

To provide a piezoelectric ceramic capable of stably forming a piezoelectric element that is small in mechanical loss when driven with great amplitude at high speed.SOLUTION: A piezoelectric ceramic comprises, as a main component, a compound containing Pb, Zr, Ti, Zn, Nb, Mn and O as constituent elements and having a Perovskite-based structure, wherein, in X-ray diffraction measurements using Cu-K α-rays, a total ratio ((IZT+IZnO) / IP×100) of a maximum peak intensity IZT expressed at 34.0°≤2θ≤35.0° and a maximum peak intensity IZnO expressed at 35.5°≤2θ≤37.0° with respect to a maximum peak intensity IP expressed at 20.0°≤2θ≤40.0° is 0.3% or greater.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to piezoelectric ceramics, a piezoelectric element, and a method for manufacturing the same. [Background technology]

[0002] Piezoelectric elements are used in sensor elements, power generation elements, etc. by utilizing the positive piezoelectric effect, which converts mechanical energy into electrical energy. Piezoelectric elements are also used in vibrators, sound generators, actuators, ultrasonic motors, pumps, etc. by utilizing the inverse piezoelectric effect, which converts electrical energy into mechanical energy. Furthermore, piezoelectric elements are also used in circuit elements, vibration control elements, etc. by using both the positive piezoelectric effect and the inverse piezoelectric effect.

[0003] Among piezoelectric elements, piezoelectric transformers, vibrators, ultrasonic motors, etc. are continuously driven under conditions where large amplitudes occur, such as at resonance points, and therefore the elements themselves tend to generate heat. Heat generation in piezoelectric elements leads to deterioration or loss of piezoelectric properties, and therefore needs to be suppressed. Heat generation in piezoelectric elements is caused by mechanical and electrical losses that occur during operation. For this reason, materials with small both of the aforementioned losses, called hard piezoelectric materials or hard materials, are used in the above-mentioned piezoelectric elements. In hard piezoelectric materials, it is important that the mechanical quality factor Qm is high as an indicator of small mechanical loss, and that the dielectric tangent tanδ is small as an indicator of small electrical loss.

[0004] One such low-loss hard piezoelectric material is lead zirconate titanate (Pb(Zr,Ti)O) which has a perovskite structure. 3 It has been proposed to reduce loss by using a basic composition of PZT (principal zirconate titanate) and incorporating various elements into the composition.

[0005] For example, a piezoelectric ceramic composition that has a high mechanical quality factor Qm and can be fired at a relatively low temperature is known that contains as its main component a compound having a perovskite structure and that contains Pb, Zn, Nb, Ti, Zr, and O as constituent elements (Patent Documents 1 and 2).

[0006] Also, as a means for increasing the mechanical quality factor Qm of PZT-based piezoelectric ceramics, it is known to set the area ratio of crystal grains having a domain size of 100 nm or less to 30% or more (Patent Document 3). [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Special Publication No. 54-18400 [Patent Document 2] JP 2001-181037 A [Patent Document 3] JP 2017-92280 A Summary of the Invention [Problem to be solved by the invention]

[0008] According to the piezoelectric ceramic compositions described in Patent Documents 1 and 2, piezoelectric elements having a high mechanical quality factor Qm can be obtained, but there is a problem in that the mechanical quality factor Qm of the obtained piezoelectric element may not be the intended value due to slight variations in the manufacturing conditions, such as the mixing ratio of raw materials and the firing temperature.

[0009] In addition, the piezoelectric ceramic described in Patent Document 3 has a large number of domain walls, which are the boundaries between domains, because the domain size in the ceramic particles is small. It is believed that the domain walls in the ceramic particles move within the particles when a piezoelectric element is driven at high speed and large amplitude, and this movement causes mechanical loss. For this reason, there is a concern that the piezoelectric ceramic described in Patent Document 3, which contains a large number of domain walls, will cause large mechanical loss when a piezoelectric element formed therefrom is driven at high speed and large amplitude.

[0010] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a piezoelectric ceramic that can stably produce a piezoelectric element that has small mechanical loss when driven at high speed and large amplitude. [Means for solving the problem]

[0011] The present inventors conducted various investigations to solve the above-mentioned problems, and discovered that the problems could be solved by making the piezoelectric ceramic contain, in addition to a compound having a perovskite structure, a Zn-containing oxide having a different crystal structure, and thus completed the present invention.

[0012] That is, one aspect of the present invention for solving the above-mentioned problems is to provide a compound having a perovskite structure, which contains Pb, Zr, Ti, Zn, Nb, Mn and O as constituent elements, and which is a main component, and which has a maximum peak intensity I appearing at 20.0°≦2θ≦40.0° in X-ray diffraction measurement using Cu-Kα radiation. P The maximum peak intensity I appearing at 34.0° ≦ 2θ ≦ 35.0° ZT and the maximum peak intensity I appearing at 35.5° ≦ 2θ ≦ 37.0° ZnO The ratio of the total to ((I ZT +I ZnO ) / I P × 100) is 0.3% or more.

[0013] Another aspect of the present invention is a piezoelectric element including the above-mentioned piezoelectric ceramic and electrodes electrically connected to the piezoelectric ceramic.

[0014] Furthermore, another aspect of the present invention is an ultrasonic transducer including the above-mentioned piezoelectric element and a pair of block bodies that sandwich the piezoelectric element from one axial direction. Effect of the Invention

[0015] According to the present invention, it is possible to provide a piezoelectric ceramic that can stably produce a piezoelectric element that has small mechanical loss when driven at high speed and large amplitude. [Brief description of the drawings]

[0016] [Figure 1] FIG. 1 is a schematic perspective view showing a structure of a multi-layer piezoelectric element according to one aspect of the present invention; [Diagram 2] Left side view of the multi-layer piezoelectric element shown in Figure 1 [Diagram 3] A-A' cross-sectional view of the multi-layer piezoelectric element shown in Figure 1 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] The configuration and effects of the present invention will be described below with reference to the drawings, together with the technical ideas. However, the mechanism of action includes assumptions, and the correctness of such assumptions does not limit the present invention. Note that the description of a numerical range (two numerical values ​​connected with "~") includes the numerical values ​​described as the lower and upper limits.

[0018] In this specification, "driving at high speed and large amplitude" of a piezoelectric element means driving at a resonance frequency, or driving under conditions where the vibration velocity measured by a laser Doppler vibrometer is 0.62 m / s or higher.

[0019] [Piezoelectric ceramics] A piezoelectric ceramic according to one aspect of the present invention (hereinafter, sometimes simply referred to as "first aspect") contains, as constituent elements, Pb, Zr, Ti, Zn, Nb, Mn, and O, and is mainly composed of a compound having a perovskite structure, and has a maximum peak intensity I appearing at 20.0°≦2θ≦40.0° in X-ray diffraction measurement using Cu-Kα radiation. P The maximum peak intensity I appearing at 34.0° ≦ 2θ ≦ 35.0° ZT and the maximum peak intensity I appearing at 35.5° ≦ 2θ ≦ 37.0° ZnO The ratio of the total to the total ({(I ZT +I ZnO ) / I P}×100) is 0.3% or more.

[0020] The first side contains Pb, Zr, Ti, Zn, Nb, Mn, and O as constituent elements and is mainly composed of a compound having a perovskite structure. As a result, the compound having a perovskite structure is mainly composed of Pb(Zr,Ti)O 3 -Pb(Zn,Nb)O 3 -Pb(Mn,Nb)O 3 and when used as a piezoelectric element, a large displacement amount can be obtained with respect to the applied voltage, and the mechanical loss during driving can be suppressed.

[0021] It is preferable that the first side has a composition formula represented by the following formula (1) in terms of achieving a larger displacement amount and lower mechanical loss.

[0022] [Chemical formula]

[0023] However, a, b, x, y, and z in the formula are real numbers satisfying 0 < a ≤ 0.10, 0.45 ≤ b ≤ 0.60, 0 < x ≤ 0.85, 0 < y < 1.0, 0 < z ≤ 0.10, and x + y + z = 1.0, respectively.

[0024] Here, the first side contains Pb, Zr, Ti, Zn, Nb, Mn and O as constituent elements, is mainly composed of a compound having a perovskite structure, and has a composition represented by the formula (1), which are confirmed by the following procedures. First, the piezoelectric ceramic is pulverized to prepare a powdered sample. When the piezoelectric ceramic forms a piezoelectric element, it is preferable to remove parts other than the piezoelectric ceramic, such as electrodes and coatings, before pulverizing. However, for piezoelectric elements such as laminated piezoelectric elements described below, in which it is difficult to separate the piezoelectric ceramic part from other parts and the proportion of the piezoelectric ceramic part is higher than the other parts, the element may be pulverized to prepare a powdered sample. Next, the diffraction line profile of the obtained powdered sample is measured by an X-ray diffractometer (XRD) using Cu-Kα radiation, and it is determined that the piezoelectric ceramic is mainly composed of a compound having a perovskite structure when the ratio of the strongest diffraction line intensity in the diffraction profile derived from other structures to the strongest diffraction line intensity in the profile derived from the perovskite structure is 10% or less. In addition, when the piezoelectric ceramic portion is not separated from the other portions and the piezoelectric element is pulverized to obtain a powdered sample, if a peak that is clearly derived from a portion other than the piezoelectric ceramic, such as an electrode, is observed in the diffraction line profile, the peak is excluded and the above-mentioned comparison of the strongest line intensity is performed. Next, for the powdered sample confirmed to be mainly composed of a compound having a perovskite structure, a composition analysis is performed using a high-frequency inductively coupled plasma optical emission spectrometry (ICP), an ion chromatography device, or an X-ray fluorescence analysis device (XRF). Then, from the results of the composition analysis, the presence or absence of each element other than oxygen is confirmed, and if the presence is confirmed, it is determined that the piezoelectric ceramic contains each of the elements. Furthermore, from the results of the composition analysis, the content ratio of elements other than oxygen is calculated, and if the content ratio is the ratio in the above formula (1), it is determined that the piezoelectric ceramic has a composition represented by the above formula (1).

[0025] The first aspect may contain other additive elements or compounds as long as it contains the above-mentioned elements as constituent elements and is mainly composed of a compound having a perovskite structure. Examples of additive elements include ABO 3 In the perovskite structure represented by the formula: Ca, Sr, Ba, Ag, La, Ce, Bi, etc. are dissolved in the A site, and Mg, Fe, Co, Ni, Ta, W, etc. are dissolved in the B site. Examples of compounds include a glassy grain boundary phase derived from a component added to lower the sintering temperature.

[0026] The first aspect is the maximum peak intensity I that appears at 20.0°≦2θ≦40.0° in X-ray diffraction measurements using Cu-Kα radiation. P The maximum peak intensity I appearing at 34.0° ≦ 2θ ≦ 35.0° ZT and the maximum peak intensity I appearing at 35.5° ≦ 2θ ≦ 37.0° ZnO The ratio of the total to the total ({(I ZT +I ZnO ) / I P Zn-containing oxide ratio is 0.3% or more. This results in a piezoelectric element having a high mechanical quality factor Qm.

[0027] In the first aspect, when X-ray diffraction measurement is performed using Cu-Kα radiation, the maximum peak intensity I appears in the range of 2θ from 20.0° to 40.0°. P is derived from the compound having a perovskite structure, which is the main component. On the other hand, the maximum peak intensity I ZT is an oxide containing Zn and Ti (Zn p Ti q O r (where p, q and r are real numbers)) and the maximum peak I appears in the 2θ range of 35.5° to 37.0°. ZnO is derived from zinc oxide (ZnO). P I ZT and I ZnOA high value of the Zn-containing oxide ratio, which is the ratio of the total of the Zn-containing oxide and the perovskite structure, means that the content ratio of the Zn-containing oxide having a crystal structure different from the perovskite structure is relatively high. When this ratio is 0.3% or more, a piezoelectric element with a high mechanical quality factor Qm can be obtained. The reason for this is not clear at present, but since the origin of Zn and / or Ti, which are constituent elements of the Zn-containing oxide, is a compound with a perovskite structure, it is presumed that the generation of the Zn-containing oxide introduces lattice defects into the perovskite structure, and the action of the defect dipole formed thereby inhibits the movement of the domain wall, which contributes in some way. From the viewpoint of obtaining a higher mechanical quality factor Qm, the Zn-containing oxide ratio is preferably 0.5% or more, and more preferably 1.0% or more. The upper limit of the Zn-containing oxide ratio is 10% or less, as described above, since the first side is mainly composed of a compound with a perovskite structure. From the viewpoint of obtaining a piezoelectric element with a large displacement per applied voltage by increasing the ratio of the compound with a perovskite structure, which is the main component, the Zn-containing oxide ratio is preferably 5% or less.

[0028] Here, the Zn-containing oxide ratio is calculated by the following procedure. First, the piezoelectric ceramic is made into a powder sample by the above-mentioned method, and its XRD profile is measured. Next, the obtained results are analyzed using crystal structure analysis software (JADE, manufactured by Lightstone Co., Ltd.), and the maximum peak intensity I P , maximum peak intensity I at 34.0° ≦ 2θ ≦ 35.0° ZT , and the maximum peak I at 35.5°≦2θ≦37.0° ZnO Finally, the obtained I P , I ZT , and I ZnO Using {(I ZT +I ZnO ) / I P}×100 is calculated and used as the Zn-containing oxide ratio.

[0029] In the first aspect, the average particle size r avgIt is preferable that the average particle diameter r is 2.5 μm or more. This makes it possible to form larger domains in the particles when used in a piezoelectric element, and to reduce the number of domain walls, thereby suppressing mechanical loss caused by the movement of the domain walls when driven at high speed and with large amplitude. avg is more preferably 2.7 μm or more, further preferably 3.0 μm or more, and particularly preferably 3.5 μm or more. avg Although there is no particular upper limit, it is preferable to set the upper limit to 10 μm or less in order to prevent a decrease in mechanical strength due to coarse particles.

[0030] Here, the average grain size r avg is determined in the following procedure. First, platinum is vapor-deposited on the surface of the piezoelectric ceramic to impart conductivity, and a measurement sample is prepared. Regarding the piezoelectric ceramic in the piezoelectric element, if there is a part exposed on the element surface, platinum is vapor-deposited on that part to prepare a measurement sample. If the piezoelectric ceramic is not exposed on the surface of the piezoelectric element, the piezoelectric ceramic part is exposed by polishing, grinding, cutting, etching, etc., and then heat treatment (thermal etching) is performed at a temperature of 900 to 960 ° C for about 15 to 30 minutes, and platinum is vapor-deposited to prepare a measurement sample. Next, the measurement sample is observed with a scanning electron microscope (SEM), and 4 to 6 photographs are taken at a magnification that allows about 60 to 200 particles to fit in the field of view. Next, the photographs are processed to calculate the circle equivalent diameter of each particle. Finally, the obtained circle equivalent diameter r of each particle is calculated. i From the number of particles n calculated from this, the average particle size r is calculated using the following formula (2). avg is calculated and this is taken as the average grain size of the piezoelectric ceramic.

[0031]

number

[0032] [Manufacturing method of piezoelectric ceramics] The piezoelectric ceramic according to the first aspect is manufactured by, for example, mixing powders of compounds containing one or more elements selected from Pb, Zr, Ti, Zn, and Nb to obtain a mixed powder containing the elements, calcining the mixed powder to obtain a calcined powder, mixing the calcined powder with a compound containing Mn, forming the mixture into a predetermined shape to obtain a molded body, and firing the molded body. This manufacturing method will be described below.

[0033] The powder of the compound used as the raw material is not limited in composition and particle size, so long as it can be fired to obtain the piezoelectric ceramic according to the first aspect. The compound constituting the powder may contain an additive element other than the elements described above. Examples of compounds that can be used include PbO and Pb 3 O 4 However, ZrO 2 However, TiO 2 ZnO is a Zn-containing compound, and Nb is a Nb-containing compound. 2 O 5 etc. are listed.

[0034] The method for mixing the raw material powders is not particularly limited as long as the powders are mixed uniformly while preventing impurities from being mixed in, and either dry mixing or wet mixing may be used. When wet mixing using a ball mill is used, mixing may be performed for about 8 to 24 hours, for example.

[0035] The calcination conditions are not limited as long as the raw materials react to obtain a calcined powder mainly composed of a perovskite-type compound represented by the above-mentioned composition formula, and may be, for example, 700°C to 1000°C in an air atmosphere for 2 to 8 hours. If the calcination temperature is too low or the calcination time is too short, there is a risk that unreacted raw materials or intermediate products will remain. On the other hand, if the calcination temperature is too high or the calcination time is too long, there is a risk that a compound with the desired composition will not be obtained due to the volatilization of Pb and Zn, or the product will solidify and become difficult to disintegrate, resulting in a decrease in productivity.

[0036] The Mn-containing compound to be mixed with the calcined powder is not limited in composition and particle size as long as it can be sintered to obtain the piezoelectric ceramic according to the first aspect. 3 The calcined powder and the Mn-containing compound can be mixed in the same manner as the raw material powder described above. Although the Mn-containing compound may be mixed simultaneously with the raw material powder described above, it is preferable to mix the Mn-containing compound with the calcined powder, since this makes it easier to obtain a piezoelectric ceramic with a high content of Zn-containing oxide.

[0037] The calcined powder mixed with the Mn-containing compound can be molded by any method commonly used for molding ceramic powders, such as uniaxial pressing of the powder, extrusion molding of a clay containing the powder, or casting of a slurry in which the powder is dispersed.

[0038] Here, when the piezoelectric ceramic is obtained as the piezoelectric ceramic layer 10 of the multi-layer piezoelectric element 100 shown in Figs. 1 to 3, the following molding method can be used.

[0039] First, the calcined powder mixed with the Mn-containing compound is mixed with a binder or the like to form a slurry or clay, which is then molded into a sheet to obtain a green sheet containing the calcined powder. Conventional methods such as the doctor blade method and extrusion molding can be used to mold the sheet.

[0040] Next, an electrode pattern that will become the internal electrode 20 after firing is formed on the green sheet containing the calcined powder. The electrode pattern may be formed by a conventional method, and a method of printing or applying a paste containing an electrode material is preferable in terms of cost. When forming the electrode pattern by printing or applying, a powder (co-material) or glass frit having the same composition and crystal structure as the piezoelectric ceramic after firing may be contained in the paste in order to improve the adhesive strength to the piezoelectric ceramic after firing.

[0041] In addition, as a multilayer piezoelectric element having a structure different from those shown in Figures 1 to 3, there is also one in which the internal electrodes are electrically connected to each other through through holes (vias) penetrating the piezoelectric ceramic layers. When manufacturing a multilayer piezoelectric element having such a structure, prior to forming the electrode pattern, through holes are formed in the obtained green sheet by punching or irradiation with laser light, and the through holes are filled with an electrode material before or after forming the electrode pattern. The filling method is not particularly limited, but a method of printing a paste containing the electrode material is preferable in terms of cost.

[0042] Finally, a predetermined number of green sheets on which electrode patterns are formed are stacked and the sheets are bonded together to obtain a molded product. The stacking and bonding may be performed by a conventional method, and a method in which the green sheets are thermocompressed together by the action of a binder is preferred from the viewpoint of cost.

[0043] The compact obtained by the above procedure is fired to become the piezoelectric ceramic according to the first aspect after the binder is removed as necessary. The firing conditions may be appropriately set in consideration of the sinterability of the calcined powder and the durability of the electrode material when the compact contains it. When firing a compact containing copper (Cu) or nickel (Ni) as the electrode material, it is preferable to set the firing atmosphere to be a reducing or inert atmosphere in order to prevent oxidation. Examples of firing conditions for a compact containing neither copper (Cu) nor nickel (Ni) as the electrode material include 900°C to 1200°C in an air atmosphere for 1 hour to 5 hours. If the firing temperature is too low or the firing time is too short, there is a risk that the piezoelectric ceramic with the desired characteristics cannot be obtained due to insufficient densification. On the other hand, if the firing temperature is too high or the firing time is too long, there is a risk that the composition will deviate due to the volatilization of Pb or Zn, or that the characteristics will deteriorate due to the generation of coarse particles. Furthermore, if the molded body contains an electrode material, there is a risk that the melting or diffusion of the electrode material will prevent the piezoelectric ceramic or piezoelectric element from having the desired characteristics. In order to avoid such inconveniences caused by a too high firing temperature and to reduce material costs by using a low melting point material for the electrode material, it is preferable to set the firing temperature to 1100°C or lower. When multiple piezoelectric ceramics or piezoelectric elements are to be obtained from one molded body, the molded body may be divided into several blocks prior to firing.

[0044] [Piezoelectric element] A piezoelectric element according to another aspect of the present invention (hereinafter, sometimes simply referred to as the "second aspect") includes the piezoelectric ceramic according to the first aspect described above, and an electrode electrically connected to the piezoelectric ceramic. Since the second aspect includes the piezoelectric ceramic according to the first aspect, the mechanical quality factor Qm is large, and the piezoelectric element generates little heat even when driven at high speed and with large amplitude.

[0045] In the second aspect, the material, shape and arrangement of the electrodes are not particularly limited as long as they can apply a desired voltage to the piezoelectric ceramic. Examples of the material of the electrodes include silver (Ag), copper (Cu), gold (Au), platinum (Pt), palladium (Pd), nickel (Ni) and alloys thereof. Examples of the shape and arrangement of the electrodes include those that cover almost the entire specific surface of the piezoelectric ceramic. In addition, when the piezoelectric element is a multi-layer piezoelectric element 100 having a layered structure of piezoelectric ceramic layers 10 and internal electrodes 20 as shown in Figs. 1 to 3, in addition to the external electrode 30 for applying a voltage to the piezoelectric ceramic part exposed on the element surface and extracting the voltage generated in the piezoelectric ceramic part, the piezoelectric element may be provided with connecting conductors 31 and 32 that cover the exposed parts of the internal electrodes and connect them to every other layer.

[0046] [Manufacturing method of piezoelectric element] The piezoelectric element according to the second aspect is manufactured by forming electrodes on the surface of the piezoelectric ceramic according to the first aspect and performing a polarization process. This manufacturing method will be described below.

[0047] The electrodes can be formed by a commonly used method such as applying or printing a paste containing an electrode material onto the surface of the piezoelectric ceramic and baking it, or by evaporating an electrode material onto the surface of the piezoelectric ceramic.

[0048] The conditions of the polarization treatment are not particularly limited as long as the spontaneous polarization can be aligned without causing damage such as cracks in the piezoelectric ceramics. One example is application of an electric field of 1 kV / mm to 5 kV / mm at a temperature of 100°C to 180°C.

[0049] [Ultrasonic transducer] An ultrasonic transducer according to yet another aspect of the present invention (hereinafter, sometimes simply referred to as the "third aspect") includes a piezoelectric element according to the second aspect, and a pair of block bodies sandwiching the piezoelectric element from one axial direction. This ultrasonic transducer is known as a Langevin type transducer. The Langevin type transducer may be a so-called bolt-tightened Langevin transducer in which the block bodies are fastened to the piezoelectric element by bolts to sandwich them together. The Langevin type transducer generates ultrasonic vibrations by supplying electric energy to the piezoelectric element, and operates to transmit the ultrasonic vibrations to the outside via the block bodies. The third aspect includes the piezoelectric element according to the second aspect, and thus the transducer generates less heat when driven at high speed and with large amplitude, and can be driven stably for a long time.

[0050] The material of the block used in the third aspect is not particularly limited as long as it can efficiently transmit the ultrasonic vibration generated by the piezoelectric element, and for example, titanium alloy, aluminum alloy, SUS, etc. can be used. EXAMPLES

[0051] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0052] Example 1 [Manufacturing of piezoelectric ceramics] As the starting material, high purity Pb 3 O 4 , ZrO 2 , TiO 2 , ZnO and Nb 2 O 5 The powder was prepared and each powder was mixed with a mixture of Pb{(Zr 0.4029 Ti 0.3871 )(Zn 1 / 3 Nb 2 / 3 ) 0.21}O 3The mixture was weighed out so as to obtain a calcined powder having a perovskite structure represented by the formula: and wet-mixed in a ball mill using zirconia balls. After mixing, the mixed powder from which the dispersion medium was removed was calcined in air at 820°C for 3 hours to obtain a calcined powder. The calcined powder thus obtained was crushed, and then high-purity MnCO 3 The powder was mixed at 0.5% by mass, and an acrylic binder was added, followed by uniaxial press molding at a load of 2 tf to obtain a disk-shaped molded body having a diameter of 10 mm. The obtained molded body was fired in air at 1100°C for 2 hours to obtain the piezoelectric ceramic according to Example 1.

[0053] [Measuring the Zn-containing oxide ratio in piezoelectric ceramics] The Zn-containing oxide ratio of the resulting piezoelectric ceramic was measured and calculated by the above-mentioned method, and was found to be 0.3%.

[0054] [Measuring the average grain size of piezoelectric ceramics] The average grain size r avg was determined by the method described above, and r avg =2.7μm.

[0055] [Manufacturing of test piezoelectric elements] After applying Ag paste to both sides of the aforementioned disk-shaped piezoelectric ceramic, the ceramic was passed through a belt furnace set at 800°C and baked to form electrodes. The piezoelectric ceramics after the electrodes were formed were subjected to polarization treatment for 15 minutes in silicon oil at 150° C. with an electric field strength of 2.2 kV / mm to obtain a piezoelectric element for testing.

[0056] [Mechanical quality factor Qm measurement of test piezoelectric element] After 24 hours had passed since polarization, the relationship between frequency and impedance of the test piezoelectric element was measured using an impedance analyzer, and the mechanical quality factor Qm was calculated by the resonance-antiresonance method. As a result of the measurement, the mechanical quality factor Qm was 1269.

[0057] (Examples 2 to 4) [Manufacturing of piezoelectric ceramics] MnCO to be mixed with calcined powder 3 The piezoelectric ceramics of Examples 2 to 4 were manufactured in the same manner as Example 1, except that the amount of powder was 1.0 mass% (Example 2), 1.5 mass% (Example 3), and 2.0 mass% (Example 4) with respect to the calcined powder.

[0058] [Measurement of Zn-containing oxide ratio and average grain size of piezoelectric ceramics] The Zn-containing oxide ratio and average grain size r avg was measured and calculated in the same manner as in Example 1. In Example 2, the Zn-containing oxide ratio was 0.7% and r avg In Example 3, the Zn-containing oxide ratio was 1.6% and r avg In Example 4, the Zn-containing oxide ratio was 1.3% and r avg became 4.6 μm.

[0059] [Manufacturing of test piezoelectric elements and measurement of mechanical quality factor Qm] A test piezoelectric element was manufactured from the piezoelectric ceramic according to each example by the same method as in Example 1, and the mechanical quality factor Qm was measured and calculated. As a result, the mechanical quality factor Qm was 1954 in Example 2, 2110 in Example 3, and 834 in Example 4.

[0060] Comparative Example 1 [Manufacturing of piezoelectric ceramics] MnCO mixed with the calcined powder in Example 1 3 The powder was mixed with the powder of the starting material at the same time, and the MnCO 3 A piezoelectric ceramic according to Comparative Example 1 was produced in the same manner as in Example 1, except that no powder was added.

[0061] [Measurement of Zn-containing oxide ratio and average grain size of piezoelectric ceramics] The Zn-containing oxide ratio of the obtained piezoelectric ceramic was measured and calculated in the same manner as in Example 1. No peaks were observed in the ranges of 34.0°≦2θ≦35.0° and 35.5°≦2θ≦37.0° in the XRD profile, and the Zn-containing oxide ratio was 0%. In addition, the average grain size r avg When measured and calculated in the same manner as in Example 1, it was found to be 2.3 μm.

[0062] [Manufacturing of test piezoelectric elements and measurement of mechanical quality factor Qm] A test piezoelectric element was manufactured from the piezoelectric ceramic according to the comparative example in the same manner as in Example 1, and the mechanical quality factor Qm was measured and calculated.

[0063] The results of the examples and comparative examples are shown in Table 1.

[0064] [Table 1]

[0065] Comparing the Examples and Comparative Examples, it can be seen that the piezoelectric ceramics according to the Examples, in which the Zn-containing oxide ratio is 0.3% or more and in which the presence of Zn-containing oxides in addition to compounds with a perovskite structure is confirmed, exhibit a high mechanical quality factor Qm when made into a piezoelectric element. From these results, it can be said that in piezoelectric ceramics containing Pb, Zr, Ti, Zn, Nb, Mn, and O as constituent elements and mainly composed of compounds with a perovskite structure, by setting the Zn-containing oxide ratio to 0.3% or more, a piezoelectric element with a high mechanical quality factor Qm can be formed. Also, in the piezoelectric ceramics according to the Examples, the average grain size r avg It can also be seen that the average grain size r is larger than that of the comparative example. Previous studies have confirmed that piezoelectric ceramics composed of large grains tend to have a high mechanical quality factor Qm. avg It is also considered that this contributes to the improvement of the mechanical quality factor Qm of the piezoelectric element. [Industrial Applicability]

[0066] According to the present invention, it is possible to provide a piezoelectric ceramic that can stably obtain a piezoelectric element with small mechanical loss when driven at high speed and large amplitude. When such a piezoelectric ceramic is formed into an ultrasonic vibrator, a piezoelectric transformer, or the like and driven at high speed and large amplitude, the amount of heat generated during driving is reduced compared to conventional ones, resulting in high performance and reliability. Therefore, a piezoelectric element including the piezoelectric ceramic according to the present invention can be suitably used for ultrasonic vibrators, piezoelectric transformers, and the like. [Explanation of symbols]

[0067] 100 Multilayer piezoelectric element 10 Piezoelectric ceramic layer 20 Internal electrode 30 External electrode 31, 32 Connecting conductor

Claims

1. A piezoelectric ceramic comprising, as constituent elements, Pb, Zr, Ti, Zn, Nb, Mn and O, having a perovskite-type structure as a main component, containing a Zn-containing oxide having a crystal structure different from the perovskite-type structure, and in X-ray diffraction measurement using Cu-Kα rays, The maximum peak intensity I that appears at 20.0° ≤ 2θ ≤ 40.0° and is derived from the compound having the perovskite-type structure Ｐ with respect to Zn ｐ Ti ｑ O ｒ (where p, q, and r are each real numbers), the maximum peak intensity I appearing at 34.0° ≤ 2θ ≤ 35.0° ＺＴ and The maximum peak intensity I appearing at 35.5° ≤ 2θ ≤ 37.0°, which is derived from zinc oxide (ZnO) ＺｎＯ with Total ratio ((I ＺＴ + I ＺｎＯ ) / I Ｐ × 100) is 0.3% or more and 1.6% or less a piezoelectric ceramic.

2. The average particle size r of the contained particles ａｖｇ The piezoelectric ceramic according to claim 1, wherein the average particle size r of the contained particles is 2.5 μm or more.

3. The piezoelectric ceramic according to claim 1 or 2, wherein the composition formula is represented by the following formula (1). 【Chemical 1】 (However, a, b, x, y and z in the formula are respectively 0 < a ≤ 0.10, 0.45 ≤ b ≤ 0 . 60, 0 < x ≤ 0.85, 0 < y < 1.0, 0 < z ≤ 0.10 and x + y + z = 1.0 are real numbers satisfying the above conditions.)

4. A piezoelectric element comprising the piezoelectric ceramic according to any one of claims 1 to 3 and an electrode electrically connected to the piezoelectric ceramic.

5. An ultrasonic vibrator comprising the piezoelectric element according to claim 4 and a pair of block bodies sandwiching the piezoelectric element from a uniaxial direction.

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