Piezoelectric ceramic, ceramic electronic component, and method for manufacturing piezoelectric ceramic

Abstract

The piezoelectric ceramic according to the present invention contains a perovskite compound that contains at least Pb, Zr, Ti, Mn, and Nb. The crystallite diameter calculated from X-ray crystal structure analysis of the perovskite compound is at least 190 nm and not more than 320 nm. The absolute value of the product of the piezoelectric constant d31 and the mechanical quality factor Qm is at least 410 nC / N.

Description

Piezoelectric ceramics, ceramic electronic components, and method for manufacturing piezoelectric ceramics

[0001] The present invention relates to a piezoelectric ceramic, a ceramic electronic component, and a method for manufacturing a piezoelectric ceramic.

[0002] In recent years, there has been a strong demand for smaller mobile devices and thinner televisions, and electronic components are also being required to be even smaller and lower in height. Piezoelectric resonant-driven high-power devices are considered advantageous for achieving smaller and lower in height because they can achieve large displacement even in small shapes. Lead zirconate titanate (hereinafter referred to as "PZT"), which has excellent piezoelectric properties, is widely used as a ceramic material for this type of piezoelectric ceramic electronic component.

[0003] Piezoelectric resonant-driven high-power devices are characterized by high displacement accuracy due to voltage proportional control using the inverse piezoelectric effect, but a weakness is that the amount of displacement is small in small electric fields. Therefore, research and development is being conducted on compositions and manufacturing methods to increase the amount of displacement of piezoelectric ceramics in small electric fields.

[0004] Patent Document 1 discloses a method for manufacturing a piezoelectric ceramic electronic component, which comprises blending a PZT raw material so that the ratio α / β of the Mn compounding molar ratio α and the Nb compounding molar ratio β exceeds 0.50, forming the resulting ceramic molded body, and firing the resulting ceramic molded body in a reducing atmosphere with an oxygen partial pressure of 0.25 Pa or less.

[0005] In Patent Document 2, a ceramic compact formed by molding a PZT raw material is fired for a short time at a first predetermined temperature, and then fired for a long time at a second predetermined temperature lower than the first predetermined temperature, and the Pb present at the grain boundaries is converted into a ratio per unit weight of the sintered body and is found to be 6 × 10 －４ A method for manufacturing a piezoelectric ceramic is described, characterized in that:

[0006] In Patent Document 3, a ceramic molded body formed by molding a PZT raw material is heated under an oxygen partial pressure of 9.87 × 10 －２ MPa or more, 1.01 x 10 －１ The patent document describes a method for producing piezoelectric ceramics, characterized in that the material is fired in an oxygen-rich atmosphere of 0.1 MPa or less.

[0007] JP 2010-215418 A JP 2017-092279 A International Publication No. 2020 / 017325

[0008] In order to increase the displacement of piezoelectric ceramics in a small electric field, the sintered body is made denser to increase the piezoelectric constant d ３１ and mechanical quality factor Q ｍ Improved piezoelectric device performance ３１ Q ｍ However, the methods of Patent Documents 1 to 3 did not provide sufficient improvement.

[0009] In the air atmosphere firing that is usually performed with PZT compounds, if the top firing temperature is low, such as 900 to 1000°C, sintering diffusion does not occur sufficiently, making it difficult to obtain a dense sintered body. On the other hand, if the top firing temperature is set to a high temperature exceeding 1000°C, for example, 1050 to 1200°C, in order to obtain a dense sintered body, a large amount of lead oxide components with low vapor pressure volatilize from within the grains, causing thermal diffusion to become dominant, and the densification of the ceramics progresses before crystallization has progressed sufficiently, resulting in a high relative dielectric constant (ε ３３ Ｔ / ε ０ ) is difficult to obtain, and the piezoelectric constant d ３１ was also low.

[0010] The present invention has been made in view of the above circumstances, and aims to provide a sintered body having a high density and a low piezoelectric constant d ３１ and mechanical quality factor Q ｍ By improving the piezoelectric device performance in a small electric field, ３１ Q ｍ The object of the present invention is to provide a piezoelectric ceramic having improved properties.

[0011] The piezoelectric ceramic of the present invention contains a perovskite-type compound containing at least Pb, Zr, Ti, Mn, and Nb, and the crystallite diameter of the perovskite-type compound calculated by X-ray crystal structure analysis is 190 nm or more and 320 nm or less, and the piezoelectric constant d ３１ and mechanical quality factor Q ｍ The absolute value of the product of this is 410 nC / N or more.

[0012] The ceramic electronic component of the present invention is characterized by comprising a piezoelectric body containing the piezoelectric ceramic of the present invention and external electrodes.

[0013] The method for producing a piezoelectric ceramic of the present invention includes a ceramic calcination powder preparation step of preparing ceramic raw materials containing at least a Pb compound, a Zr compound, a Ti compound, a Mn compound, and a Nb compound, and calcining the ceramic raw materials to produce a calcined ceramic powder; a molding step of forming the calcined ceramic powder into a ceramic green body; and a firing step of firing the ceramic green body to obtain a sintered body, wherein the firing step is carried out in an atmosphere having an oxygen partial pressure of 3.62 × 10 －１３ MPa or more, 2.01 x 10 －１１ The firing is carried out in a low-oxygen atmosphere of 0.1 MPa or less, at a top temperature of 900°C or more and 1000°C or less, and for a holding time at the top temperature of 24 hours or more and 40 hours or less.

[0014] According to the present invention, the piezoelectric constant d ３１ and mechanical quality factor Q ｍ By improving the piezoelectric device performance in a small electric field, ３１ Q ｍ It is possible to provide a piezoelectric ceramic having improved properties.

[0015] Fig. 1 is a cross-sectional view schematically showing an example of a first embodiment of a ceramic electronic component. Fig. 2 is a cross-sectional view schematically showing an example of a second embodiment of a ceramic electronic component. Fig. 3 is a cross-sectional view schematically showing an example of a third embodiment of a ceramic electronic component. Fig. 4 shows the relative dielectric constants ε of the piezoelectric ceramics of Samples 1 to 4. ３３ Ｔ / ε ０ 5 is a graph showing the k of the piezoelectric ceramics of Samples 1 to 4, which corresponds to a graph showing the k of the piezoelectric ceramics of Samples 1 to 4, where the holding time at the top firing temperature of 1000°C is changed. ３１ 6 is a graph showing the Pb content at the TEM grain boundaries of the piezoelectric ceramics of Samples 1, 2, and 4. FIG. ３１ and mechanical quality factor Q ｍ The product of ３１ Q ｍ7 is a graph showing the piezoelectric constant d of the piezoelectric ceramics of Samples 2 and 5 to 8, which corresponds to a graph showing the holding time at the top firing temperature of 1000°C. ３１ and mechanical quality factor Q ｍ The product of ３１ Q ｍ 8 is a graph showing the electromechanical coupling coefficient k of the piezoelectric ceramics of Samples 2 and 5 to 8, which is obtained by changing the firing top temperature while maintaining the firing top temperature for 24 hours. ３１ and mechanical quality factor Q ｍ The product of ３１ ２ Q ｍ 9 is a graph showing the crystallite diameter of the piezoelectric ceramics of Samples 1 to 4, where the holding time at the top firing temperature was 24 hours and the top firing temperature was changed. FIG. 10 is a graph showing the flexural strength of the piezoelectric ceramics of Samples 1 to 4, where the holding time at the top firing temperature of 1000°C was changed.

[0016] The piezoelectric ceramic, ceramic electronic component, and method for manufacturing the piezoelectric ceramic of the present invention will be described below. However, the present invention is not limited to the following configurations, and can be modified as appropriate within the scope of the present invention. Note that a combination of two or more of the individual desirable configurations of the present invention described below also constitutes the present invention.

[0017] <Piezoelectric ceramic> The piezoelectric ceramic of the present invention contains a perovskite-type compound containing at least Pb, Zr, Ti, Mn, and Nb, and has a crystallite diameter of 190 nm or more and 320 nm or less as calculated by X-ray crystal structure analysis of the perovskite-type compound, and a piezoelectric constant d ３１ and mechanical quality factor Q ｍ The absolute value of the product of this is 410 nC / N or more.

[0018] The piezoelectric ceramic of the present invention contains a perovskite compound containing Pb, Zr, Ti, Mn, and Nb, and has a composition in which at least Mn and Nb are added to PZT ceramics. The composition of the piezoelectric ceramic of the present invention can be identified by press-molding the sintered piezoelectric ceramic and then analyzing it with fluorescent X-rays.

[0019] Furthermore, the piezoelectric ceramic of the present invention may contain trace amounts of Hf, Fe, Cl, Si, Al, etc. as unavoidable impurities, provided that the properties of the piezoelectric ceramic are not impaired.

[0020] The piezoelectric ceramic of the present invention has a crystallite diameter of 190 nm or more and 320 nm or less, as calculated by X-ray crystal structure analysis of the perovskite compound. Preferably, it is 190 nm or more and 270 nm or less. More preferably, the piezoelectric ceramic of the present invention has a crystallite diameter of 190 nm or more and 270 nm or less when the grain diameter is 4.2 μm or more and 6.3 μm or less.

[0021] For example, X-ray crystal structure analysis is carried out by filling a piezoelectric ceramic sample into a commonly used X-ray crystal structure analyzer, and scanning the sample with a copper tube CuK under the conditions of an acceleration voltage of 30 kV, a current of 15 mA, a step interval of 0.02°, and a scanning speed of 4° / min. α This can be done by a focusing method using a wavelength of 0.15418 nm.

[0022] The grain diameter is the D50 value obtained by observing the surface of a sintered piezoelectric ceramic sample with an SEM, measuring the volume distribution of at least several tens of particles using image analysis software, and determining the Heywood diameter.

[0023] The piezoelectric ceramic of the present invention has a piezoelectric constant d ３１ and mechanical quality factor Q ｍ When the absolute value of the product of the piezoelectric constant d is 410 nC / N or more, a piezoelectric device with a large displacement can be obtained. ３１ and mechanical quality factor Q ｍ It is preferable that the absolute value of the product of the piezoelectric constant d ３１ and mechanical quality factor Q ｍThe absolute value of the product may be, for example, 600 nC / N or less.

[0024] The piezoelectric ceramic of the present invention has an electromechanical coupling coefficient k ３１ and mechanical quality factor Q ｍ It is preferable that the product of k and k is 330 or more. When the above value is 330 or more, a piezoelectric device with a large displacement amount can be obtained. ３１ and the mechanical quality factor Q ｍ The product of k and k is more preferably 350 or more, and even more preferably 400 or more. ３１ and the mechanical quality factor Q ｍ The product of may be, for example, 600 or less.

[0025] The properties of the piezoelectric ceramic of the present invention can be measured as follows: ３１ The resonant frequency (fr) and anti-resonant frequency (fa) of each sample are measured using an impedance analyzer, and the resonant frequency (fr) is calculated from the following formula:

[0026]

[0027] Here, r=(π / 2)·(fa / fr).

[0028] Piezoelectric constant d ３１ is the electromechanical coupling coefficient k measured above ３１ Dielectric constant ε ３３ Ｔ and elastic compliance S １１ Ｅ It is calculated by multiplying the square root of the product of the dielectric constant ε ３３ Ｔ is calculated by measuring the capacitance of the sample at a frequency of 1 kHz using an impedance analyzer. １１ Ｅ can be calculated from the measurement results of the resonance frequency (fr) using an impedance analyzer using the following formula: １１ Ｅ = 1 / (4ρ L ２ ・fr ２ ) (2) where ρ is the density of the sample, and L is the length of the sample.

[0029] Mechanical quality factor Q ｍ is the resonant frequency (fr) measured using an impedance analyzer and the resonant resistance (R １ ) and series capacitance (C １ ) is calculated using the following formula: ｍ = 1 / (2πfrR １ C １ ) (3)

[0030] <Method for Manufacturing Piezoelectric Ceramics> Next, a method for manufacturing a piezoelectric ceramic of the present invention will be described. The method for manufacturing a piezoelectric ceramic of the present invention includes a ceramic calcined powder preparation step of preparing ceramic raw materials containing at least a Pb compound, a Zr compound, a Ti compound, a Mn compound, and a Nb compound, and calcining the ceramic raw materials to produce a calcined ceramic powder, a molding step of molding the calcined ceramic powder into a ceramic green body, and a firing step of firing the ceramic green body to obtain a sintered body, wherein the firing step is performed in an atmosphere having an oxygen partial pressure of 3.62 × 10 －１３ MPa or more, 2.01 x 10 －１１ The firing is carried out in a low-oxygen atmosphere of 0.1 MPa or less, at a top firing temperature of 900°C or more and 1000°C or less, and for a holding time at the top firing temperature of 24 hours or more and 40 hours or less.

[0031] [Ceramics Calcination Powder Preparation Process] A ceramic raw material containing at least a Pb compound, a Zr compound, a Ti compound, a Mn compound, and a Nb compound is prepared. The form of these compounds is not particularly limited, and compounds in the form of oxides, carbonates, chlorides, hydroxides, metal organic compounds, etc. of the respective metals can be used. The ceramic raw materials are weighed so that the desired composition ratio is achieved after sintering. Next, these weighed materials are placed in a ball mill or the like containing a grinding medium such as partially stabilized zirconia, and thoroughly wet-mixed using pure water or an organic solvent. After dehydration, the mixture is calcined in air at a temperature of 930°C or higher and 1080°C or lower to produce a ceramics calcination powder.

[0032] [Forming Step] Next, after crushing the calcined ceramic powder, an organic binder such as polyvinyl alcohol resin is added, and a slurry is produced by media-less wet dispersion mixing or wet pulverization using a ball mill or the like equipped with pulverization media. This slurry is then spray-dried to produce granulated powder for molding. This granulated powder is molded to produce a ceramic molded body.

[0033] [Firing and degreasing treatment] The ceramic compact is placed in a sheath and placed in a furnace for firing and degreasing treatment. The firing and degreasing treatment is carried out in an air atmosphere using a muffle furnace or the like. The firing profile involves increasing the temperature inside the furnace to a predetermined temperature (e.g., 400°C or higher and 500°C or lower) at a predetermined temperature increase rate (e.g., 0.1°C / min or higher and 4°C / min or lower), degreasing for a predetermined time (e.g., 1 hour or higher and 3 hours or lower), and then decreasing the temperature at a predetermined temperature decrease rate (e.g., 1°C / min or higher and 6°C / min or lower) to complete the firing and degreasing treatment. The firing and degreasing treatment is an optional process.

[0034] [Firing step] Next, the main firing (firing step) is performed. The firing step is performed under an oxygen partial pressure of 3.62 × 10 －１３ MPa or more, 2.01 x 10 －１１ The firing profile is as follows: the temperature in the furnace is raised to a predetermined temperature (e.g., 250°C or higher and 350°C or lower) at a predetermined temperature rise rate (e.g., 0.5°C / min or higher and 4°C / min or lower), and the temperature is maintained for a predetermined time (e.g., 1 hour or higher and 3 hours or lower), and the firing atmosphere is changed to H ２ and N ２ and humidify (H ２ / N ２ / WD), after creating the low-oxygen atmosphere, the firing top temperature is increased to 900°C or higher and 1000°C or lower at a predetermined heating rate (e.g., 0.5°C / min or higher and 4°C / min or lower), and the firing top temperature is maintained for 24 hours or higher and 40 hours or lower. After that, the temperature is decreased at a predetermined temperature decrease rate (e.g., 1°C / min or higher and 6°C / min or lower), thereby completing the firing process and obtaining a sintered body (piezoelectric ceramic).

[0035] The top firing temperature is the piezoelectric device performance d of the resulting piezoelectric ceramics. ３１ Q ｍThe point where the piezoelectric device performance k ３１ ２ Q ｍ In terms of increasing the temperature, the firing temperature is preferably 925° C. or higher and 975° C. or lower. More preferably, the firing top temperature is 935° C. or higher and 965° C. or lower, and the firing top temperature holding time is 24 hours or higher and 32 hours or lower.

[0036] The general mechanism of crystallization of perovskite compounds is said to be that first, crystal nuclei are generated, followed by growth of the crystal nuclei. Here, it is known that the generation of crystal nuclei occurs between the glass transition temperature and the melting point, particularly near the surface diffusion temperature (Homma Tsuyoshi, "Crystallization of Glass" 26 [4] pp. 33-37 (2012)). On the other hand, the presence of impurities such as unreacted lead oxides at the grain boundaries can slow down the growth rate of the crystal nuclei. Until now, it has been thought that the piezoelectric constant d ３１ Materials with high mechanical quality factor Q ｍ was low at under 150.

[0037] In the method for producing the piezoelectric ceramic of the present invention, an acceptor element such as a Mn compound is added, and N ２ H, which has a lower oxygen partial pressure than gas ２ / N ２ By firing in a / WD atmosphere, the valence of the Mn compound is reduced. By reducing the valence of the Mn compound, sintering diffusion via oxygen vacancies is promoted, and a dense piezoelectric ceramic sintered body can be obtained. In addition, H ２ / N ２ By selectively removing unreacted lead from the grain boundaries in a / WD atmosphere, conditions are created that facilitate crystallization. Furthermore, by holding the sintered body for a long period of time (24 to 40 hours) at a temperature between 900°C and 1000°C, which is the optimum temperature range for crystallization, the sintered body becomes dense and has a high Q. ｍ However, the piezoelectric constant d ３１ It is believed that piezoelectric ceramics with high properties can be obtained.

[0038] <Ceramic Electronic Component> The ceramic electronic component of the present invention is characterized by comprising a piezoelectric body containing the piezoelectric ceramic of the present invention and external electrodes.

[0039] Preferably, the piezoelectric body is a piezoelectric ceramic electronic component having an input section and an output section, and a voltage signal supplied to the input section is transformed and output from the output section.

[0040] An example of a ceramic electronic component will be described below. Fig. 1 is a cross-sectional view schematically showing an example of a first embodiment of a ceramic electronic component. As the first embodiment, an example of a piezoelectric actuator is shown.

[0041] This piezoelectric actuator has a laminated sintered body 6 including piezoelectric bodies 4a to 4h formed of the piezoelectric ceramic of the present invention and internal electrodes 5a to 5g, with external electrodes 7a and 7b formed on the outer surface of the laminated sintered body 6. Piezoelectric bodies 4b, 4d, 4f, and 4h are polarized in the direction of arrow A, and piezoelectric bodies 4c, 4e, and 4g are polarized in the direction of arrow B. In other words, piezoelectric bodies 4b to 4h are configured so that the polarization direction is opposite for each layer.

[0042] The laminated sintered body 6 is formed by alternately stacking piezoelectric elements 4a to 4h and internal electrodes 5a to 5g, with the internal electrodes 5a, 5c, 5e, and 5g being electrically connected to one external electrode 7a, and the internal electrodes 5b, 5d, and 5f being electrically connected to the other external electrode 7b.

[0043] The internal electrode material and the external electrode material are not particularly limited, but Ag and Ag--Pd are preferably used.

[0044] When a voltage is applied to the external electrodes 7a and 7b, this piezoelectric actuator is displaced in the direction of arrow X due to the inverse piezoelectric effect, and mechanical energy is extracted, allowing various electronic devices to be controlled with high precision.

[0045] In the first embodiment, the piezoelectric bodies 4a to 4h are formed of the piezoelectric ceramic of the present invention, so that the piezoelectric constant d ３１ and mechanical quality factor Q ｍ Therefore, it is possible to provide a piezoelectric actuator having high piezoelectric device performance in a minute electric field.

[0046] This piezoelectric actuator can be manufactured as follows.

[0047] A conductive paste for the internal and external electrodes is prepared. Furthermore, ceramic green sheets are produced using the slurry used in the molding process of the piezoelectric ceramic manufacturing method of the present invention described above. The conductive paste is applied to the surface of the ceramic green sheets by screen printing or the like to form a predetermined conductive pattern. Next, the ceramic green sheets with the conductive pattern formed thereon are stacked in a predetermined direction, and then a ceramic green sheet without the conductive pattern formed thereon is placed on top and thermocompression bonded to produce a laminated compact. This process corresponds to the molding process in the piezoelectric ceramic manufacturing method of the present invention.

[0048] Next, this laminated compact is subjected to the firing and degreasing treatment (optional step) and firing step in the method for producing a piezoelectric ceramic of the present invention, to obtain a laminated sintered compact 6 in which the piezoelectric bodies 4a to 4h and the internal electrodes 5a to 5g are arranged alternately. At this stage, the piezoelectric ceramic of the present invention is produced in the laminated sintered compact.

[0049] Thereafter, external electrodes 7a, 7b are formed on the outer surfaces of the laminated sintered body 6 by using a method such as vacuum deposition. After this, an electric field is applied to the external electrodes 7a, 7b for a predetermined time under heating, and polarization is performed in the directions of arrows A and B, thereby producing a piezoelectric actuator.

[0050] 2 is a cross-sectional view schematically showing an example of a second embodiment of a ceramic electronic component, which is a piezoelectric transformer.

[0051] This piezoelectric transformer is configured such that a piezoelectric body 8 formed from the piezoelectric ceramic of the present invention has an input section 9 and an output section 10, and a voltage signal supplied to the input section 9 is transformed and output from the output section 10.

[0052] Specifically, the input section 9 has a layered structure in which piezoelectric bodies 11a to 11j and internal electrodes 12a to 12i are alternately stacked, with input electrodes 13a and 13b, which are external electrodes, formed on the upper surface of the piezoelectric body 11a and the lower surface of the piezoelectric body 11j, and the internal electrodes 12a to 12h electrically connected to the input electrodes 13a and 13b. The piezoelectric bodies 11a, 11c, 11e, 11g, and 11i are polarized in the direction of arrow D, and the piezoelectric bodies 11b, 11d, 11f, 11h, and 11j are polarized in the direction of arrow C. In other words, the piezoelectric bodies 11a to 11j are configured so that the polarization direction is opposite for each layer.

[0053] The output section 10 has a single-layer structure with no internal electrodes, and an output electrode 14, which is an external electrode, is formed on one end surface and is polarized in the direction of arrow E.

[0054] When an AC voltage of a resonant frequency is applied to the input electrodes 13a and 13b of the piezoelectric transformer thus constructed, the voltage is converted into mechanical energy by the inverse piezoelectric effect, and mechanical vibration is excited. This mechanical vibration is then converted into electrical energy by the piezoelectric effect, and a voltage signal boosted according to the capacitance ratio between the input section 9 and the output section 10 is output from the output electrode 14.

[0055] In the second embodiment, the piezoelectric bodies 8, 11a to 11j are formed of the piezoelectric ceramic of the present invention, so that the piezoelectric constant d ３１ and mechanical quality factor Q ｍ Therefore, it is possible to provide a piezoelectric transformer having high piezoelectric device performance in a minute electric field.

[0056] In the second embodiment, the internal electrode material and the external electrode material are not particularly limited, but Ag and Ag--Pd can be preferably used.

[0057] This piezoelectric transformer can be manufactured in the same manner as the above-mentioned piezoelectric actuator, as follows.

[0058] A conductive paste for the internal and external electrodes is prepared. Furthermore, ceramic green sheets are produced using the slurry used in the molding process of the manufacturing method of the piezoelectric ceramic of the present invention described above. The conductive paste is applied to the surface of this ceramic green sheet by screen printing or the like, and a predetermined conductive pattern is formed in the area corresponding to the input section 9. Next, a predetermined number of ceramic green sheets with the conductive patterns formed thereon are stacked, and then thermocompression-bonded to produce a laminated compact. This process corresponds to the molding process in the manufacturing method of the piezoelectric ceramic of the present invention.

[0059] Next, this laminated compact is subjected to the firing and degreasing treatment (optional step) and firing step in the method for producing a piezoelectric ceramic of the present invention, to obtain a sintered body in which the input section 9 has a laminated structure in which the piezoelectric bodies 11a to 11j and the internal electrodes 12a to 12i are alternately arranged, and the output section 10 has a single-layer structure. At this stage, the piezoelectric ceramic of the present invention is produced in the sintered body.

[0060] Thereafter, input electrodes 13a and 13b are formed as external electrodes on the upper and lower surfaces of input section 9 using a method such as vacuum deposition, and output electrode 14 is further formed as an external electrode on the end surface of output section 10. After this, an electric field is applied between input electrodes 13a and 13b and output electrode 14 for a predetermined time while heated, polarizing output section 10 in the direction of arrow E. Furthermore, while heated to a predetermined temperature, an electric field is applied between input electrode 13a and input electrode 13b for a predetermined time so that the polarization direction of input section 9 is reversed for each layer, thereby completing the polarization process and completing the piezoelectric transformer.

[0061] 3 is a cross-sectional view schematically showing an example of a third embodiment of the ceramic electronic component, which is another example of a piezoelectric transformer.

[0062] In the third embodiment, as in the second embodiment, the piezoelectric body 15 formed of the piezoelectric ceramic of the present invention has an input portion 16 and an output portion 17, and is configured so that a voltage signal supplied to the input portion 16 is transformed and output from the output portion 17.

[0063] In this piezoelectric transformer, both the input section 16 and the output section 17 have a laminated structure with internal electrodes, and the inter-electrode distances of the internal electrodes are different between the input section 16 and the output section 17. That is, the input section 16 has a laminated structure in which piezoelectric bodies 18a to 18e and internal electrodes 19a to 19d are alternately laminated, and input electrodes 20a and 20b are formed on the side surfaces of the input section 16. Specifically, the internal electrodes 19a and 19c are electrically connected to one input electrode 20a, and the internal electrodes 19b and 19d are electrically connected to the other input electrode 20b. The piezoelectric bodies 18b to 18d are polarized in the direction of arrow F or the direction of arrow G so that the polarization direction is opposite for each layer.

[0064] On the other hand, the output section 17 has a layered structure in which piezoelectric bodies 21a to 21i and internal electrodes 22a to 22i are alternately stacked, and output electrodes 23a and 23b are formed on the side surfaces of the output section 17. Specifically, the internal electrodes 22a, 22c, 22e, 22g, and 22i are electrically connected to one output electrode 23a, and the internal electrodes 22b, 22d, 22f, and 22h are electrically connected to the other output electrode 23b. The piezoelectric bodies 21b to 21i are polarized in the direction of arrow H or the direction of arrow I so that the polarization direction is opposite for each layer.

[0065] In the third aspect, the inter-electrode distances of the internal electrodes 22a to 22i of the output section 17 are made different from those of the input section 16 so that the inter-electrode distances of the internal electrodes 22a to 22i of the output section 17 are shorter than the inter-electrode distances of the internal electrodes 19a to 19d of the input section 16.

[0066] When an AC voltage of a resonant frequency is applied to the input electrodes 20a and 20b of the piezoelectric transformer thus constructed, the voltage is converted into mechanical energy by the inverse piezoelectric effect, and mechanical vibration is excited. This mechanical vibration is then converted into electrical energy by the piezoelectric effect, and a voltage signal stepped down in accordance with the capacitance ratio is output from the output electrodes 23a and 23b.

[0067] In the third embodiment, the piezoelectric bodies 18a to 18e and 21a to 21i are formed of the piezoelectric ceramic of the present invention, and therefore, similarly to the second embodiment, the piezoelectric constant d ３１ and mechanical quality factor Q ｍTherefore, it is possible to provide a piezoelectric transformer having high piezoelectric device performance in a minute electric field.

[0068] In the third embodiment, the internal electrode material and the external electrode material are not particularly limited, but Ag and Ag--Pd can be preferably used.

[0069] This piezoelectric transformer can be manufactured in the same manner as the above-mentioned piezoelectric actuator and piezoelectric transformer, as follows.

[0070] A conductive paste for the internal and external electrodes is prepared. Furthermore, two types of ceramic green sheets (input ceramic green sheets and output ceramic green sheets) with different thicknesses are produced using the slurry used in the molding process of the piezoelectric ceramic manufacturing method of the present invention. A conductive paste is applied to the surfaces of these ceramic green sheets by screen printing or the like to form a predetermined conductive pattern. Next, a predetermined number of ceramic green sheets with the conductive patterns formed are stacked, and then ceramic green sheets without the conductive patterns are placed on both ends and thermocompression-bonded to produce a laminated compact. This process corresponds to the molding process in the piezoelectric ceramic manufacturing method of the present invention.

[0071] Next, this laminated compact is subjected to the firing and degreasing treatment (optional step) and firing step in the method for producing a piezoelectric ceramic of the present invention, thereby obtaining a sintered body having an input section 16 with a laminated structure in which piezoelectric bodies 18a to 18e and internal electrodes 19a to 19d are alternately arranged, and an output section 17 with a laminated structure in which piezoelectric bodies 21a to 21i and internal electrodes 22a to 22i are alternately arranged, with the internal electrodes having different inter-electrode distances. At this stage, the piezoelectric ceramic of the present invention is produced in the sintered body.

[0072] Thereafter, using a method such as vacuum deposition, input electrodes 20a, 20b and output electrodes 23a, 23b are formed as external electrodes on both sides of the input section 16 and the output section 17. After this, an electric field is applied for a predetermined time under heating so that the polarization direction is reversed for each layer, thereby performing a polarization process, and a piezoelectric transformer is produced.

[0073] The ceramic electronic component of the present invention is not limited to the above-described embodiment, and may be, for example, a piezoelectric resonator or a piezoelectric filter, as other examples of ceramic electronic components.

[0074] The present specification discloses the following: <1> A piezoelectric ceramic material containing a perovskite-type compound containing at least Pb, Zr, Ti, Mn, and Nb, wherein the crystallite diameter of the perovskite-type compound calculated by X-ray crystal structure analysis is 190 nm or more and 320 nm or less, and the piezoelectric constant d ３１ and mechanical quality factor Q ｍ The absolute value of the product of is 410 nC / N or more.

[0075] <2> Electromechanical coupling coefficient k ３１ and the mechanical quality factor Q ｍ The piezoelectric ceramic according to <1> above, wherein the product of

[0076] <3> The piezoelectric ceramic according to <1> or <2> above, wherein the crystallite diameter is 190 nm or more and 270 nm or less when the grain diameter is 4.2 μm or more and 6.3 μm or less.

[0077] <4> A ceramic electronic component comprising a piezoelectric body containing the piezoelectric ceramic according to any one of <1> to <3> above, and external electrodes.

[0078] <5> A method for producing a piezoelectric ceramic, the method comprising: preparing a ceramic raw material containing at least a Pb compound, a Zr compound, a Ti compound, a Mn compound, and an Nb compound; calcining the ceramic raw material to produce a calcined ceramic powder; forming the calcined ceramic powder into a ceramic molded body; and firing the ceramic molded body to obtain a sintered body, the firing step being carried out in an atmosphere having an oxygen partial pressure of 3.62 × 10 －１３ MPa or more, 2.01 x 10 －１１ 1. A method for producing piezoelectric ceramics, comprising the steps of: firing in a low-oxygen atmosphere of 1000 MPa or less at a top firing temperature of 900°C or more and 1000°C or less; and maintaining the top firing temperature for 24 hours or more and 40 hours or less.

[0079] Examples that more specifically disclose the piezoelectric ceramic of the present invention are given below, but the present invention is not limited to these examples.

[0080] [Preparation of Samples 1 to 8] PbO and ZrO were used as ceramic raw materials. ２ , TiO ２ , Nb ２ O ５ , MnCO ３ The main component composition after firing was PbO (67.80-68.63 wt%), ZrO ２ (17.20-17.36wt%), TiO ２ (11.49-12.10wt%), MnO (0.59-0.64wt%), Nb ２ O ５ The ceramic raw materials were weighed out so that the total weight of the ceramic raw materials was 1.97-2.06 wt %. All of the ceramic raw materials for Samples 1 to 8 had the same composition. Next, these weighed materials were placed in a ball mill together with partially stabilized zirconia balls and wet mixed and ground for 185 minutes. After that, the materials were dehydrated and dried, and then calcined at a temperature of 1030°C to produce calcined ceramic powder.

[0081] Next, this ceramic calcined powder was crushed, and then an organic binder such as polyvinyl alcohol resin was added and subjected to media-less wet dispersion mixing to prepare a slurry. This was then spray-dried to prepare granulated powder for press molding. This granulated powder was then press-molded to produce a ceramic compact.

[0082] The ceramic compact was placed in a sheath and placed in a furnace for firing and degreasing. The firing and degreasing treatment was carried out using a muffle furnace in an air atmosphere. The firing profile consisted of heating the furnace to 450°C at a heating rate of 0.5°C / min, holding the temperature for 2 hours, and then cooling the temperature at a rate of 1°C / min or more and 6°C / min or less to complete the firing and degreasing treatment.

[0083] Next, the main firing (firing step) was carried out. The firing profile was as follows: the temperature inside the furnace was raised to 300°C at a temperature rise rate of 3°C / min and held for 1 hour. Next, the temperature was raised to the top firing temperature of levels 1) to 8) in Table 1 and held for a predetermined time, and then the temperature was lowered at a rate of 1°C / min or more and 6°C / min or less to complete the firing step. The oxygen partial pressure in the firing step was 3.62 x 10 －１３ MPa or more, 2.01 x 10 －１１ The sintered bodies obtained in the levels 1) to 8) were designated as samples 1 to 8.

[0084] For evaluation of piezoelectric properties, Samples 1 to 8 were cut with a dicer into a shape of 13 mm length × 3 mm width × 0.9 mm thickness. The cut samples were subjected to polarization treatment using an oil bath or the like at a temperature of 150°C and an electric field strength of 3 kV / mm for 30 minutes.

[0085] [Piezoelectric properties] <relative dielectric constant ε ３３ Ｔ / ε ０ The capacitance of each sample at a frequency of 1 kHz was measured using an impedance analyzer (Agilent Technologies: 4294A), and this value was multiplied by the thickness of the sample. The result was then divided by the product of the dielectric constant of vacuum and the electrode area to determine the relative dielectric constant (ε ３３ Ｔ / ε ０ ) was calculated.

[0086] <Electromechanical coupling coefficient k ３１ Using an impedance analyzer (Agilent Technologies: 4294A), the resonant frequency (fr) and anti-resonant frequency (fa) of each sample were measured, and the electromechanical coupling coefficient k was calculated from the above formula (1). ３１ was calculated.

[0087] <Piezoelectric constant d ３１ > The electromechanical coupling coefficient k measured above ３１ Dielectric constant ε ３３ Ｔ and elastic compliance S １１ Ｅ The piezoelectric constant d is obtained by multiplying the square root of the product of ３１ The dielectric constant ε ３３ Ｔwas calculated by measuring the capacitance of the sample at a frequency of 1 kHz using an impedance analyzer. １１ Ｅ was calculated from the above formula (2) using the measurement results of the resonance frequency (fr) by an impedance analyzer.

[0088] <Mechanical quality factor Q ｍ The resonance frequency (fr) measured using an impedance analyzer (Agilent Technologies: 4294A) and the resonance resistance (R １ ) and series capacitance (C １ ) from the following equation, which includes the mechanical quality factor Q ｍ was calculated. ｍ = 1 / (2πfrR １ C １ )

[0089] [Crystallite diameter] Samples were loaded into an X-ray diffractometer, and X-ray diffraction measurements were performed on samples 1-4 and 6 using a copper tube CuKα (wavelength 0.15418 nm) under the following conditions: acceleration voltage 30 kV, current 15 mA, step interval 0.02°, and scan rate 4° / min. The full width at half maximum of the obtained X-ray diffraction peak for the (111) plane of the PZT-based compound was read from the graph, and the crystallite diameter was calculated by substituting each value into the Scherrer equation, with a Scherrer coefficient of 0.9 and an instrument constant of 0.16. The full width at half maximum indicates the width of the diffraction line at half the height of the diffraction line intensity.

[0090] [Grain diameter] Samples 1 to 8, in which the sample surfaces were exposed after the firing process, were observed using a field emission scanning electron microscope under the following conditions: Pretreatment: Pt sputtering (current 30 mA, 60 seconds) SEM observation conditions: acceleration voltage 5 kV, working distance (WD) 10 mm Observation signal: secondary electron image Using image analysis software, the volume distribution of 50 or more particles for each sample was measured by tracing the particle interface, and the D50 value of the Heywood diameter was taken as the grain diameter.

[0091] [Flexural Strength] Using a three-point bending tester, the stress at break was measured for at least 10 samples (N=10 or more) under the conditions of a load cell of 50 N and a distance between supports of 9 mm, and the average value was taken as the flexural strength.

[0092] [TEM Grain Boundary Pb] After the sintering, target regions of the samples were sampled using a focused ion beam (FIB) to obtain samples for observation with a transmission electron microscope (TEM). For each sample, point analysis was performed using TEM-EDX (energy dispersive X-ray spectroscopy) at four points on the grain boundaries and six points within the grains, and the average value (atom %) of Pb at the grain boundaries was calculated.

[0093] The firing conditions and evaluation results for each sample are shown in Table 1.

[0094]

[0095] In Table 1, samples marked with * are comparative examples outside the scope of the present invention.

[0096] The partial pressure of oxygen is 3.62 x 10 －１３ MPa or more, 2.01 x 10 －１１ The piezoelectric ceramics of Samples 2 to 4 and 6 obtained by firing at a firing pressure of 1000 MPa or less, a firing top temperature of 900°C or more and 1000°C or less, and a holding time at the firing top temperature of 24 hours or more and 40 hours or less, have a crystallite diameter of 190 nm or more and 320 nm or less, and a piezoelectric constant d ３１ and mechanical quality factor Q ｍ The absolute value of the product of d and d was 410 nC / N or more. ３１ Q ｍ The absolute value of d was 410 nC / N or more, but the crystallite diameter was small at 70 nm. It is considered necessary to maintain the firing temperature at least for 24 hours to promote crystallization. Sample 5 of level 5), in which the firing temperature was 850°C and the holding time was 24 hours, ３１ Q ｍ The absolute value of was smaller than 410 nC / N, and the crystallite size was very small. ３１ Q ｍ In order to increase the absolute value of and the crystallite diameter, it is considered necessary for the firing temperature to be 900°C or higher. Samples 7 and 8, which are firing temperatures exceeding 1000°C, have ３１ Q ｍThe absolute value of the electromechanical coupling coefficient k was 410 nC / N or more, but it was estimated that the crystallite diameter exceeded 320 nm, and the lead component with low vapor pressure was volatilized during firing at high temperature and for a long time. ３１ is estimated to be lower.

[0097] FIG. 4 shows the relative dielectric constant ε of the piezoelectric ceramics of Samples 1 to 4. ３３ Ｔ / ε ０ 4 is a graph showing the relative dielectric constant ε of the piezoelectric ceramic obtained by further holding the firing temperature at 1000°C for 8 hours. ３３ Ｔ / ε ０ It was found that by holding the top firing temperature (1000°C) for 24 to 40 hours, the relative dielectric constant of the piezoelectric ceramics became higher than when the holding time was shorter than 24 hours.

[0098] FIG. 5 shows the k values ​​of the piezoelectric ceramics of Samples 1 to 4. ３１ 1 is a graph showing the amount of Pb at the TEM grain boundaries of the piezoelectric ceramics of Samples 1, 2, and 4. ３１ It was found that both the amount of Pb in the TEM grain boundaries and the amount of Pb in the TEM grain boundaries decreased as the holding time at the top firing temperature (1000° C.) increased.

[0099] FIG. 6 shows the piezoelectric constants d ３１ and mechanical quality factor Q ｍ The product of ３１ Q ｍ 6 is a graph showing the piezoelectric constant d of the piezoelectric ceramic obtained by further holding the firing temperature at 1000°C for 8 hours. ３１ and mechanical quality factor Q ｍ The product of ３１ Q ｍ By keeping the firing temperature at 1000°C for 16 to 40 hours, ３１ Q ｍ It was found that the absolute value of was 410 nC / N or more.

[0100] FIG. 7 shows the piezoelectric constants d ３１ and mechanical quality factor Q ｍ The product of ３１ Q ｍ 7 is a graph showing the piezoelectric constant d of the piezoelectric ceramic obtained by holding the top firing temperature at 900° C. for 24 hours. ３１ and mechanical quality factor Q ｍ The product of ３１ Q ｍ When the firing temperature is kept between 900°C and 1100°C for 24 hours, ３１ Q ｍ It was found that the absolute value of d was 410 nC / N or more. In particular, when the firing temperature was 935°C or more and 965°C or less, ３１ Q ｍ The absolute value of was found to be high.

[0101] FIG. 8 shows the electromechanical coupling coefficient k of the piezoelectric ceramics of Samples 2 and 5 to 8. ３１ and mechanical quality factor Q ｍ The product of ３１ ２ Q ｍ 8 is a graph showing the electromechanical coupling coefficient k of the piezoelectric ceramic obtained by holding the firing temperature at 900°C for 24 hours. ３１ and mechanical quality factor Q ｍ The product of ３１ ２ Q ｍ When the firing temperature is kept between 900°C and 1000°C for 24 hours, ３１ ２ Q ｍ It was found that k is 360 or more. In particular, when the firing top temperature is 935°C or more and 965°C or less, k ３１ ２ Q ｍ was found to be higher.

[0102] 9 is a graph showing the crystallite diameters of the piezoelectric ceramics of Samples 1 to 4, which corresponds to a graph in which the holding time at the top firing temperature of 1000° C. was changed. It was found that by holding the top firing temperature at 1000° C. for 24 to 40 hours, the crystallite diameter of the piezoelectric ceramics became 190 nm or more and 320 nm or less.

[0103] 10 is a graph showing the bending strength of the piezoelectric ceramics of Samples 1 to 4, which corresponds to a graph in which the holding time at the top firing temperature of 1000°C was changed. It was found that by holding the top firing temperature at 1000°C for 24 to 40 hours, the bending strength of the piezoelectric ceramics became 100 MPa or more.

[0104] 4a to 4h Piezoelectric bodies 5a to 5g Internal electrodes 6 Laminated sintered body 7a, 7b External electrodes 8, 11a to 11j Piezoelectric bodies 9 Input section 10 Output section 12a to 12i Internal electrodes 13a, 13b Input electrodes 14 Output electrode 15 Piezoelectric body 16 Input section 17 Output section 18a to 18e, 21a to 21i Piezoelectric bodies 19a to 19d, 22a to 22i Internal electrodes 20a, 20b Input electrodes 23a, 23b Output electrodes

Claims

1. A piezoelectric material containing a perovskite-type compound containing at least Pb, Zr, Ti, Mn, and Nb, wherein the crystallite diameter of the perovskite-type compound calculated by X-ray crystal structure analysis is 190 nm or more and 320 nm or less, and the piezoelectric constant d ３１ and mechanical quality factor Q ｍ The absolute value of the product of is 410 nC / N or more.

2. Electromechanical coupling coefficient k ３１ and the mechanical quality factor Q ｍ The piezoelectric ceramic according to claim 1, wherein the product of 3. The piezoelectric ceramic according to claim 1 or 2, wherein the crystallite diameter is 190 nm or more and 270 nm or less when the grain diameter is 4.2 μm or more and 6.3 μm or less.

4. A ceramic electronic component comprising a piezoelectric body containing the piezoelectric ceramic according to any one of claims 1 to 3 and external electrodes.

5. A method for producing a piezoelectric ceramic, comprising: a ceramic calcined powder preparation step of preparing ceramic raw materials containing at least a Pb compound, a Zr compound, a Ti compound, a Mn compound, and a Nb compound, and calcining the ceramic raw materials to produce a calcined ceramic powder; a forming step of molding the calcined ceramic powder into a ceramic molded body; and a firing step of firing the ceramic molded body to obtain a sintered body, wherein the firing step is carried out in an atmosphere having an oxygen partial pressure of 3.62 × 10 －１３ MPa or more, 2.01 x 10 －１１ 1. A method for producing piezoelectric ceramics, comprising the steps of: firing in a low-oxygen atmosphere of 1000 MPa or less at a top firing temperature of 900°C or more and 1000°C or less; and maintaining the top firing temperature for 24 hours or more and 40 hours or less.

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