Piezoelectric ceramics, piezoelectric elements and ultrasonic transducers

Abstract

To provide a piezoelectric ceramic capable of forming a piezoelectric element that is small in both mechanical loss and electrical loss during its drive.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, with the contained particles having an average particle diameter ravg of 4 μm, 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 1.0% or smaller.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). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Special Publication No. 54-18400 [Patent Document 2] JP 2001-181037 A Summary of the Invention [Problem to be solved by the invention]

[0007] In a piezoelectric ceramic composition mainly composed of a compound having a perovskite structure containing Pb, Zn, Nb, Ti, Zr, and O as constituent elements, a piezoelectric element with a high mechanical quality factor Qm can be obtained by further adding Mn. However, in this case, the dielectric tangent tanδ becomes high, and the electrical loss becomes large, which is a problem.

[0008] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide a piezoelectric ceramic that can provide a piezoelectric element in which both mechanical loss and electrical loss during operation are small. [Means for solving the problem]

[0009] In the course of research to solve the above problems, the inventors noticed that in a piezoelectric element having a large dielectric loss tangent tanδ formed from the above-mentioned piezoelectric ceramic composition, the sintered grains forming the piezoelectric ceramic have a large grain size, and that the piezoelectric ceramic contains oxides containing Zn having a crystal structure other than the perovskite structure. They then found that the above problems could be solved by making the piezoelectric ceramic into one in which the generation of such large grain sintered grains and oxides containing Zn is suppressed, and thus completed the present invention.

[0010] That is, one aspect of the present invention for solving the above-mentioned problems is to provide a composition comprising a compound having a perovskite structure as a main component, which contains Pb, Zr, Ti, Zn, Nb, Mn and O as constituent elements, the molar ratio of Mn to Ti (Mn / Ti) being 0.07 or less, and has an average particle diameter r avg The maximum peak intensity I appears at 20.0°≦2θ≦40.0° in the 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 1.0% or less.

[0011] Another aspect of the present invention is a piezoelectric element including the above-mentioned piezoelectric ceramic and electrodes electrically connected to the piezoelectric ceramic.

[0012] 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

[0013] According to the present invention, it is possible to provide a piezoelectric ceramic that can provide a piezoelectric element in which both mechanical loss and electrical loss during operation are small. [Brief description of the drawings]

[0014] [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

[0015] 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.

[0016] 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.

[0017] [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, in which the molar ratio of Mn to Ti (Mn / Ti) is 0.07 or less, and is mainly composed of a compound having a perovskite structure, and the average particle diameter r of the particles contained therein is avg The maximum peak intensity I appears at 20.0°≦2θ≦40.0° in the 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 1.0% or less.

[0018] The first aspect includes, as its main component, a compound having a perovskite structure and containing, as its constituent elements, Pb, Zr, Ti, Zn, Nb, Mn, and O. As a result, the compound having a perovskite structure is Pb(Zr,Ti)O 3 -Pb(Zn,Nb)O 3 -Pb(Mn,Nb)O 3 When used as a piezoelectric element, it is possible to obtain a large amount of displacement in response to an applied voltage and to suppress mechanical loss during operation.

[0019] The first side has a molar ratio of Mn to Ti (Mn / Ti) included as a constituent element of 0.07 or less. As a result, when used as a piezoelectric element, the dielectric loss tangent tanδ becomes smaller, and the electrical loss during driving can be suppressed. The reason for this is not clear at present but is presumed as follows. Mn is located at the same site (B site) as Ti and Zn in the perovskite structure. If the amount of Mn in the piezoelectric ceramics becomes too large, some of the contained Ti and Zn cannot exist in the perovskite structure, and Zn p Ti q O r (where p, q, and r are each real numbers) and oxides having a crystal structure other than the perovskite structure such as ZnO are generated. The presence of such oxides causes an increase in the dielectric loss tangent tanδ when used as a piezoelectric element. On the other hand, when the molar ratio (Mn / Ti) is 0.07 or less, the generation of oxides having a crystal structure other than the perovskite structure is suppressed. Therefore, the dielectric loss tangent tanδ when used as a piezoelectric element is kept low, and the electrical loss during driving becomes small. From the viewpoint of obtaining a piezoelectric element with smaller electrical loss, it is preferable that the molar ratio (Mn / Ti) is 0.05 or less. The lower limit value of the molar ratio (Mn / Ti) is not particularly limited, but from the viewpoint of obtaining a piezoelectric element with a high mechanical quality factor Qm, it is preferably 0.02 or more, and more preferably 0.03 or more.

[0020] The first side preferably has a composition formula represented by the following formula (1) in terms of achieving a larger displacement amount and lower mechanical loss.

[0021]

Chemical formula

[0022] However, a, b, x, y, and z in the formula are real numbers satisfying -0.05 ≤ a ≤ 0.05, 0.45 ≤ b ≤ 0.60, 0 < x ≤ 0.85, 0 < y < 1.0, 0.01 < z < 0.10, and x + y + z = 1.0, respectively.

[0023] Here, the following steps are performed to confirm that the first side contains Pb, Zr, Ti, Zn, Nb, Mn, and O as constituent elements, is composed mainly of a compound having a perovskite structure, has a composition represented by the formula (1), and has a molar ratio (Mn / Ti) of 0.07 or less. First, the piezoelectric ceramic is pulverized to prepare a powdered sample. When the piezoelectric ceramic forms a piezoelectric element, it is preferable to remove portions other than the piezoelectric ceramic, such as electrodes and coatings, before pulverizing. However, for piezoelectric elements such as stacked piezoelectric elements described below, which are difficult to separate from the piezoelectric ceramic portion and have a higher proportion of the piezoelectric ceramic portion than the other portions, 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 if the ratio of the strongest diffraction line intensity in the diffraction profile originating from the perovskite structure to the strongest diffraction line intensity in the profile originating from other structures is 10% or less, it is determined that the piezoelectric ceramic is mainly composed of a compound having a perovskite structure. If the piezoelectric ceramic part is not separated from the other parts and the piezoelectric element is pulverized to obtain a powdered sample, and a peak that is clearly originating from a part other than the piezoelectric ceramic, such as an electrode, is observed in the diffraction line profile, the peak is excluded and the above-mentioned strongest line intensity is compared. Next, the powdered sample confirmed to be mainly composed of a compound having a perovskite structure is subjected to composition analysis by high-frequency inductively coupled plasma optical emission spectrometry (ICP), an ion chromatography device, or an X-ray fluorescence analyzer (XRF). Then, the presence or absence of each element other than oxygen is confirmed from the results of the composition analysis, and if the presence is confirmed, it is determined that the piezoelectric ceramic contains each of the elements. In addition, from the results of the composition analysis, the content ratio of elements other than oxygen is calculated, and if this content ratio is the ratio in formula (1), it is determined that the piezoelectric ceramic has a composition represented by formula (1).Furthermore, from the results of the composition analysis, the molar ratio of Mn to Ti (Mn / Ti) is calculated, and if this value is 0.07 or less, the piezoelectric ceramic is determined to have a molar ratio of Mn to Ti (Mn / Ti) of 0.07 or less.

[0024] 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.

[0025] 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}×100) (hereinafter, may be referred to as "Zn-containing oxide ratio") is 1.0% or less. This results in a low dielectric tangent tan δ when used in a piezoelectric element.

[0026] 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 ZnO A small value of the Zn-containing oxide ratio, which is the ratio of the total of the Zn-containing oxide and the Zn-containing oxide, means that the content ratio of the Zn-containing oxide having a crystal structure different from the perovskite structure is relatively low. When this ratio is 1.0% or less, the increase in the dielectric loss tangent tanδ caused by such Zn-containing oxide is suppressed, and a piezoelectric element having a low dielectric loss tangent tanδ is obtained. In order to obtain a lower dielectric loss tangent tanδ, the Zn-containing oxide ratio is preferably low, preferably 0.5% or less, more preferably 0.3% or less, and even more preferably less than 0.3%.

[0027] 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.

[0028] The first aspect is the average particle size r avg The average particle size r is 4.0 μm or less. This reduces the difference in particle size between particles, resulting in a low dielectric tangent tan δ when used in a piezoelectric element. avgPiezoelectric ceramics with a small average grain size r are also preferred in that, when they are used in a laminated piezoelectric element (described later), even if the thickness of each layer is reduced, the amount of displacement per unit volume is not likely to decrease. avg is preferably 1.0 μm or less, and more preferably 0.8 μm or less. avg The lower limit of is not particularly limited, but is about 0.1 μm for piezoelectric ceramics obtained by a general manufacturing method. In general piezoelectric ceramics, the crystal grains are often grown sufficiently during firing to close the open pores. In this case, the average grain size r avg However, in the first aspect, the grain growth during firing is suppressed, thereby making it possible to form a piezoelectric element having both a high mechanical quality factor Qm and a low dielectric tangent tanδ, and in this respect, the first aspect is different from general piezoelectric ceramics.

[0029] In the first aspect, the particle diameter coefficient of variation CV of the particles contained is preferably 40% or less. A small particle diameter coefficient of variation CV leads to a more uniform microstructure, and a piezoelectric element having a lower dielectric tangent tanδ is obtained. The coefficient of variation CV is more preferably 38% or less.

[0030] Here, the average grain size r avg The coefficient of variation CV of the particle size is determined by 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. Next, 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 This is the average grain size of the piezoelectric ceramic. avg The value of and the aforementioned r i From the values ​​of and n, the standard deviation s of the particle size is calculated by the following formula (3). Finally, the obtained average particle size r avg From the values ​​of the standard deviation s and the mean diameter s, the coefficient of variation CV is calculated by the following formula (4), and this is regarded as the coefficient of variation CV of the grain size in 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, Nb, and Mn to obtain a mixed powder containing the elements, calcining the mixed powder to obtain a calcined powder, forming the calcined powder 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 However, MnCO is a Mn-containing compound. 3 etc. are listed.

[0034] The method for mixing the raw material powders is not particularly limited as long as each powder can be mixed uniformly while preventing the inclusion of impurities, and either dry mixing or wet mixing may be adopted. When wet mixing using a ball mill is adopted, mixing may be performed for, for example, about 8 to 24 hours. In addition, in a general method for producing piezoelectric ceramics, a Mn-containing compound is not added when mixing the raw material powders, and a method of adding the compound to the powder after calcination described later is commonly used, and this method may be adopted in the production of the first aspect.

[0035] The calcination conditions of the mixed powder 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 calcined powder obtained by calcination 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, and casting of a slurry in which the powder is dispersed.

[0037] 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.

[0038] First, the calcined powder is mixed with a binder or the like to form a slurry or a clay, which is then molded into a sheet to obtain a green sheet containing the calcined powder. Conventional methods such as a doctor blade method and an extrusion molding method can be used to mold the sheet.

[0039] 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] [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. By including the piezoelectric ceramic according to the first aspect in the second aspect, the second aspect has a low dielectric tangent tanδ while maintaining a high mechanical quality factor Qm, and is a piezoelectric element that generates little heat even when driven at high speed and large amplitude.

[0044] 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.

[0045] [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.

[0046] 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.

[0047] 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.

[0048] [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.

[0049] 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

[0050] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0051] Example 1 [Manufacturing of piezoelectric ceramics] As the starting material, high purity Pb 3 O 4 , ZrO 2 , TiO 2 , ZnO, Nb 2 O 5 and MnCO 3 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 ) 0.18 (M 1 / 3 Nb 2 / 3 ) 0.03}O 3The materials were weighed 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. The Mn / Ti molar ratio in the composition formula was 0.022. After mixing, the mixed powder from which the dispersion medium had been 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 mixed with an acrylic binder, and uniaxially pressed under a load of 2tf to obtain a disk-shaped molded body having a diameter of 10mm. The obtained molded body was fired in air at 1100°C for 2 hours to obtain a piezoelectric ceramic according to Example 1.

[0052] [Measurement of Zn-containing oxide ratio in piezoelectric ceramics] The Zn-containing oxide rate of the obtained piezoelectric ceramic was measured and calculated by the method described above. 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 rate was 0%.

[0053] [Measurement of average grain size and coefficient of variation of piezoelectric ceramics] The average grain size r avg and the coefficient of variation, CV, were determined by the method described above. avg =0.70 μm, CV=36.5%.

[0054] [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.

[0055] [Measurement of dielectric tangent of test piezoelectric element] After polarization, the dielectric tangent tan δ of the test piezoelectric element was measured 24 hours later using an LCR meter at a frequency of 1 kHz and an OSC of 1 V, resulting in a value of tan δ = 0.37%.

[0056] Example 2 And reference examples 3) [Manufacturing of piezoelectric ceramics] The amount of raw powder mixed is determined so that the composition of the calcined powder obtained is Pb{Zr 0.4029 Ti 0.3871 (Zn 1 / 3 Nb 2 / 3 ) 0.16 (M 1 / 3 Nb 2 / 3 ) 0.05}O 3 (Example 2), and Pb{Zr 0.4029 Ti 0.3871 (Zn 1 / 3 Nb 2 / 3 ) 0.13 (M 1 / 3 Nb 2 / 3 ) 0.08}O 3 What becomes ( reference Example 2) was prepared in the same manner as in Example 1, except that Example 3 was used. And reference examples The piezoelectric ceramics according to Example 3 were manufactured. The Mn / Ti molar ratio in each of the composition formulas was 0.045 (Example 2) and 0.067 (Example 3). reference Example 3).

[0057] [Measurements of Zn-containing oxide ratio, average grain size and coefficient of variation of piezoelectric ceramics] The Zn-containing oxide ratio of each of the obtained piezoelectric ceramics was measured and calculated in the same manner as in Example 1. In all of the piezoelectric ceramics, 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 The coefficient of variation CV was measured and calculated in the same manner as in Example 1. avg = 0.74 μm, CV = 35.0%, reference In Example 3, r avg =0.79 μm, CV=39.4%.

[0058] [Manufacturing of test piezoelectric elements and measurement of dielectric tangent] From each of the obtained piezoelectric ceramics, a test piezoelectric element was manufactured in the same manner as in Example 1, and the dielectric loss tangent tanδ was measured. As a result, the test piezoelectric element according to Example 2 had a tanδ of 0.31%. reference In the test piezoelectric element of Example 3, tan δ was 0.50%.

[0059] ( reference Example 4) [Manufacturing of piezoelectric ceramics] From raw powder to MnCO 3 The powder was removed, and mixing and calcination were performed. The calcined powder thus obtained was mixed with the same amount of MnCO as that mixed as the raw material powder in Example 2. 3 The same method as in Example 2 was used except that the powders were mixed and then molded. reference The piezoelectric ceramic according to Example 4 was produced.

[0060] [Measurements of Zn-containing oxide ratio, average grain size and coefficient of variation 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, and was found to be 0.9%. avg The coefficient of variation CV was measured and calculated in the same manner as in Example 1. avg =3.3 μm, CV=39.7%.

[0061] [Manufacturing of test piezoelectric elements and measurement of dielectric tangent] A piezoelectric element for testing was produced from the obtained piezoelectric ceramic in the same manner as in Example 1, and its dielectric tangent tan δ was measured, resulting in tan δ=0.63%.

[0062] Comparative Example 1 [Manufacturing of piezoelectric ceramics] From raw powder to MnCO 3 The powder is removed and mixed and calcined. The calcined powder is then reference The same amount of MnCO as that used as the raw powder in Example 3 3 Except for mixing the powder and then molding it, referenceIn the same manner as in Example 3, a piezoelectric ceramic according to Comparative Example 1 was produced.

[0063] [Measurements of Zn-containing oxide ratio, average grain size and coefficient of variation 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, and was found to be 1.6%. avg The coefficient of variation CV was measured and calculated in the same manner as in Example 1. avg =4.5 μm, CV=46.5%.

[0064] [Manufacturing of test piezoelectric elements and measurement of dielectric tangent] A piezoelectric element for testing was produced from the resulting piezoelectric ceramic in the same manner as in Example 1, and its dielectric tangent tan δ was measured, resulting in tan δ=1.17%.

[0065] The results of the examples and comparative examples are shown in Table 1.

[0066] [Table 1]

[0067] Comparing the Examples and Comparative Examples, the Zn-containing oxide ratio is 1.0% or less and the average particle size r avg but 1.0 It can be seen that the piezoelectric ceramics according to the examples, which have a particle size of 0.1 μm or less, exhibit a low dielectric tangent tan δ when used as a piezoelectric element. , reference example The piezoelectric ceramics according to the comparative example and the comparative example all contain Mn, and therefore, when used as piezoelectric elements, they can be said to exhibit a high mechanical quality factor Qm. referenceIt was confirmed that the piezoelectric ceramics according to Example 3 and Comparative Example 1 could provide piezoelectric elements having a mechanical quality factor Qm exceeding 1500. From these facts, it can be seen that the piezoelectric ceramics according to Example 3 and Comparative Example 1 contain Pb, Zr, Ti, Zn, Nb, Mn, and O as constituent elements, and are mainly composed of a compound having a perovskite structure, and the Zn-containing oxide ratio is 1.0% or less, and the average particle size ravg of the particles contained therein is 1.0 Piezoelectric ceramics having a particle size of 0.1 μm or less exhibit a high mechanical quality factor Qm and a low dielectric tangent tan δ, and it can be said that it is possible to obtain a piezoelectric element having small mechanical loss and small electrical loss during operation.

[0068] In addition, during production, Mn-containing compounds such as MnCO 3 Example 2: And reference examples 3 and mixed with the calcined powder. reference Comparing Example 4 and Comparative Example 1, the former has a lower Zn-containing oxide ratio and a smaller average particle size r at the same Mn content. avg It can also be seen that when made into a piezoelectric element, a smaller dielectric tangent tanδ can be obtained. Therefore, when it is necessary to include a large amount of Mn in the piezoelectric ceramic in order to obtain a piezoelectric element with a high mechanical quality factor Qm, it can be said that the deterioration of the dielectric tangent tanδ can be suppressed by mixing a Mn-containing compound into the raw material powder and calcining it. [Industrial Applicability]

[0069] According to the present invention, it is possible to provide a piezoelectric ceramic that can obtain a piezoelectric element with small mechanical and electrical losses during operation. When such a piezoelectric ceramic is used to form an ultrasonic vibrator, a piezoelectric transformer, or the like and driven at high speed and large amplitude, the amount of heat generated during operation 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]

[0070] 100 Multilayer piezoelectric element 10 Piezoelectric ceramic layer 20 Internal electrode 30 External electrode 31, 32 Connecting conductor

Claims

1. A material comprising Pb, Zr, Ti, Zn, Nb, Mn and O as constituent elements, a molar ratio of Mn to Ti (Mn / Ti) of 0.045 or less; The main component is a compound having a perovskite structure, The average particle size r avg of the particles contained is 1.0 μm or less, In an X-ray diffraction measurement using Cu-Kα radiation, the ratio ((I ZT +I ZnO ) / I P ×100) of the sum of a maximum peak intensity I ZT appearing at 34.0°≦2θ≦35.0° and a maximum peak intensity I ZnO appearing at 35.5°≦2θ≦37.0° to a maximum peak intensity I P appearing at 20.0°≦2θ≦40.0° is 1.0% or less, and The composition formula is represented by the following formula (1): Piezoelectric ceramics. 【Chemistry 1】 (In the formula, a, b, x, y, and z are real numbers satisfying -0.05≦a≦0.05, 0.45≦b≦0.60, 0<x≦0.85, 0.16≦y<1.0, 0.01<z<0.10, and x+y+z=1.0.)

2. 2. The piezoelectric ceramic according to claim 1, wherein the coefficient of variation C.V. of the particle size of the particles contained therein is 40% or less.

3. A piezoelectric element comprising the piezoelectric ceramic according to claim 1 or 2 and an electrode electrically connected to the piezoelectric ceramic.

4. 4. An ultrasonic transducer comprising: the piezoelectric element according to claim 3; and a pair of block bodies sandwiching the piezoelectric element in one axial direction.

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