JP5322401B2 - Piezoelectric ceramic and piezoelectric element - Google Patents

Description

  The present invention relates to a piezoelectric ceramic and a piezoelectric element, and for example, a piezoelectric ceramic and a piezoelectric element that are suitably used for a resonator, an ultrasonic vibrator, an ultrasonic motor, or a piezoelectric sensor such as an acceleration sensor, a knocking sensor, and an AE sensor. It is about.

  Conventionally, products using a piezoelectric ceramic include, for example, a filter, a piezoelectric resonator, an ultrasonic vibrator (hereinafter referred to as a concept including an oscillator), an ultrasonic motor, a piezoelectric sensor, and the like.

  In recent years, piezoelectric elements are incorporated in parts such as automobile engines and suspensions, and the pressure applied to the piezoelectric elements is sensed using the positive piezoelectric effect and used for engine combustion control and vehicle body attitude control. In particular, as a piezoelectric element used for engine control, there is an anti-knock sensor among lean burn type engines that are widely used for the purpose of cleaning exhaust gas and improving fuel consumption. Piezoelectric elements are also being used to measure combustion pressure for the purpose of stable combustion of lean gases among HCCI (Homogenous Charge Compression Ignition) engines that do not use combustion plugs, which are being considered as next-generation engines. Has been.

  Since these piezoelectric elements are mounted in an engine room, element materials having high heat resistance are required. Furthermore, in order to improve fuel efficiency, it is necessary to precisely measure the pressure in the engine cylinder and perform fine lean burn control, so output signal characteristics (pressure characteristics of generated charge) with respect to sensor pressure and temperature changes. Further, an element material having a small change in temperature characteristics) is required.

  Conventionally, PT and PZT-based materials that have high piezoelectricity, such as large P / V and large charge generated with respect to pressure, have been used for resonators and pressure sensor elements. However, since PZT and PT-based materials contain lead in a proportion of about 60% by mass of their own weight, it has been pointed out that lead elution occurs due to acid rain and causes environmental pollution. Therefore, high expectations are placed on piezoelectric materials that do not contain lead.

  Further, since PZT and PT-based materials have a Curie temperature Tc of about 200 to 300 ° C., the piezoelectric d constant deteriorates when used at a high temperature of about 200 ° C., and is 200 ° C. relative to the room temperature piezoelectric d constant. There is a great limitation on the use because of the large change in the piezoelectric d constant. For example, when used as a pressure sensor, if the piezoelectric d constant deteriorates with time, the output voltage changes even at the same pressure, and if the change in the piezoelectric d constant at 200 ° C. relative to the piezoelectric d constant at room temperature is large, the pressure and output Since the relationship with the voltage is not linear, it is difficult to calculate an accurate pressure from the output voltage.

  Therefore, materials mainly composed of bismuth layered compounds have been proposed as piezoelectric ceramic compositions not containing lead. And it has been proposed to add Mn in order to reduce the firing variation of the bismuth layered compound (for example, Patent Document 1).

Many materials mainly composed of bismuth layered compounds have a Curie temperature of 400 ° C or higher, and such materials have high heat resistance and are used in environments exposed to high temperatures such as in an engine room. There is a possibility of application as an element.
JP 2002-167276 A

  However, when the piezoelectric ceramic composition described in Patent Document 1 is fired, the fired piezoelectric ceramic has Mn dissolved in the main phase of the bismuth layered compound and at the grain boundary portion of the main phase. Mn is unevenly distributed. The part where Mn is unevenly distributed in the grain boundary portion contains a crystal phase, and this crystal phase is also precipitated between the firing ceramics where the piezoelectric ceramic and the piezoelectric ceramic are placed during firing. Since the liquid phase is generated, there is a problem that a part of the piezoelectric ceramic and the firing jig is welded.

  If the piezoelectric ceramic and the firing jig where the piezoelectric ceramic is placed are severely welded, it will be difficult to remove the piezoelectric ceramic from the firing jig, etc., or cracks and chipping will occur in the piezoelectric ceramic when removed. As a result, the yield of piezoelectric ceramics was low. In addition, the presence of a reaction phase with a firing jig or the like has been a factor of deteriorating piezoelectric characteristics. Furthermore, if the piezoelectric ceramic has a small degree of chipping reaction or a part of the firing jig is stuck to the piezoelectric ceramic, the reaction will not affect the piezoelectric characteristics. Had to be removed and was costly.

  Accordingly, an object of the present invention is to provide a piezoelectric ceramic and a piezoelectric element in which a piezoelectric ceramic and a firing jig on which the piezoelectric ceramic is placed are hardly welded during firing.

In the piezoelectric ceramic of the present invention, the composition formula is represented by Bi ₄ Ti ₃ O ₁₂ × x (A _1-α RE _α ) TiO ₃ , and A is an alkaline earth metal _β (alkali metal _1/2 Bi _1/2 ). a _1-beta, RE is a rare earth element, and the main component of 100 parts by weight satisfying 1.4 ≦ x ≦ 1.7,0.05 ≦ α ≦ 0.3,0 ≦ β ≦ 1, the Mn contains a 0.05 to 2.0 parts by mass MnO ₂ terms, a bismuth layer compound as well as the main phase, the concentration of Mn to definitive in the grain boundary portion between the main phase, the concentration of Mn in the main phase It is characterized by the following .

  The piezoelectric element according to the present invention is characterized in that a pair of electrodes are arranged opposite to each other on the surface and inside of the piezoelectric ceramic.

In the piezoelectric ceramic of the present invention , the composition formula is represented by Bi ₄ Ti ₃ O ₁₂ × x (A _1-α RE _α ) TiO ₃ , and A is an alkaline earth metal _β (alkali metal _1/2 Bi _1/2 ). a _1-beta, RE is a rare earth element, and the main component of 100 parts by weight satisfying 1.4 ≦ x ≦ 1.7,0.05 ≦ α ≦ 0.3,0 ≦ β ≦ 1, the Mn It contains a 0.05 to 2.0 parts by mass MnO ₂ terms, a bismuth layer compound as well as the main phase, by Mn is not unevenly distributed in the grain boundary portion of the front Symbol main phase, sintering of the piezoelectric ceramic When the piezoelectric ceramic is exposed to high temperatures in processes, etc., it is possible to suppress the welding of the piezoelectric ceramic and the firing jig that is in contact with the piezoelectric ceramic , the Curie temperature is high, and the absolute value of the piezoelectric constant is large. A piezoelectric ceramic is obtained .

  In addition, according to the piezoelectric element of the present invention, a pair of electrodes are arranged opposite to each other on the surface and inside of the piezoelectric ceramic, so that the piezoelectric ceramic can be removed from the firing jig after firing. The resulting defects are reduced, and an inexpensive piezoelectric element can be produced.

  The piezoelectric ceramic of the present invention is a piezoelectric ceramic having a bismuth layered compound as a main phase and containing Mn, and it is important that Mn is not unevenly distributed in the grain boundary portion of the main phase. Thereby, when a piezoelectric ceramic is exposed to high temperature by the firing process of a piezoelectric ceramic, etc., it can suppress that the firing ceramic etc. which the piezoelectric ceramic and the piezoelectric ceramic contact are welded.

  Here, Mn is not unevenly distributed in the grain boundary part. The section of the piezoelectric ceramic is mirror-finished, and the Mn element is mapped by Mn element mapping at a magnification of 5000 times with an electron microscope EPMA (Electron Probe Micro-Analysis). The fact that it is not unevenly distributed in the boundary part, that is, comparing the inside of the grain of the bismuth layered compound with the grain boundary part, indicates that there is not much Mn in the grain boundary part.

  More specifically, the fact that Mn is not unevenly distributed at the grain boundary means that the site where Mn element mapping is performed with EPMA is observed with an SEM (Scanning Electron Microscope) or the like, and the Mn concentration in the portion other than the particles of the bismuth layered compound The average of (count number) has shown the state which is not high compared with the average of the density | concentration of Mn inside the particle | grains of a bismuth layered compound. Such a state includes the following states. The concentration of Mn is almost uniform. The average of the Mn concentration (count number) in the portion other than the particles of the bismuth layered compound is lower than the average of the Mn concentration inside the particles of the bismuth layered compound.

  Conversely, Mn is unevenly distributed in the grain boundary part means that the average Mn concentration (count number) of the portion other than the particles of the bismuth layered compound is the average of the Mn concentration inside the particles of the bismuth layered compound. It is in a high state compared with. In particular, the average of the Mn concentration (count number) in the portion other than the particles of the bismuth layered compound is 1.5 times the average of the Mn concentration inside the particles of the bismuth layered compound, or the triple point of the grain boundary is When the Mn concentration is twice the average Mn concentration inside the particles of the bismuth layered compound, Mn is unevenly distributed in the grain boundary portion, and the piezoelectric ceramic and the firing jig are strongly welded. Moreover, if this high Mn density | concentration part is observed with TEM (Transmission Electron Microscope), it can confirm that there exists a crystal phase by electron beam diffraction.

  A bismuth layered compound has a plate-like crystal structure, and generally has a low sintering density. Therefore, a material serving as a sintering aid is added and fired. An example of such a substance is Mn. The material of the firing jig when firing the compact of the bismuth layered compound raw material is stabilized zirconia (including partially stabilized zirconia), high-purity alumina, spinel, and the same or similar composition as the bismuth layered compound to be fired. Ceramics such as a bismuth layered compound having a composition may be mentioned.

  Then, when the piezoelectric ceramic containing the bismuth layered compound as a main phase and firing the piezoelectric ceramic containing Mn on the ceramic firing jig described above, the piezoelectric ceramic may be welded to the firing jig. As a result of detailed observation and analysis of the surface where the piezoelectric ceramic and the firing jig were in contact, it was not the main phase of the bismuth layered compound but the precipitated phase containing a large amount of Mn. . A phase similar to the precipitated phase containing a large amount of Mn is also present between the main phases of the bismuth layered compound inside the piezoelectric ceramic, and Mn enhances the sinterability of the bismuth layered compound. A layer was generated and a piezoelectric ceramic and a firing jig were welded. By suppressing the uneven distribution of Mn in the grain boundary part, welding between the piezoelectric ceramic and the firing jig can be suppressed.

  If the piezoelectric ceramic and the firing jig are welded, cracks, chips, cracks, and the like may occur when the piezoelectric ceramic is removed from the firing jig. When the degree is large, the piezoelectric ceramic becomes defective and the yield is low. When the degree is small, it is necessary to remove a portion where cracks or cracks are generated by polishing or the like. In addition, the piezoelectric ceramics in the vicinity of the weld may have their porcelain characteristics fluctuated due to a reaction with a firing jig or the like, and it may be necessary to remove this reacting portion. However, by suppressing the uneven distribution of Mn in the grain boundary part, the piezoelectric ceramic can be used without performing such a polishing process.

  In addition, since the bismuth layered compound is a relatively brittle material, the polishing process itself is prone to damage such as chipping, and the fact that it can be used without performing a process such as polishing after firing has the reliability of a piezoelectric element using a piezoelectric ceramic. It is preferable because it improves. In particular, when used in applications where a large pressure is applied to the piezoelectric element, such as a pressure sensor, there is no minute chipping or cracks generated during polishing, and therefore breakage due to the chipping or cracking is eliminated.

In the piezoelectric ceramic of the present invention, the composition formula is represented by Bi ₄ Ti ₃ O ₁₂ × x (A _1-α RE _α ) TiO ₃ , and A is an alkaline earth metal _β (alkali metal _1/2 Bi _1/2 ). _1-β , (0 ≦ β ≦ 1), RE is a rare earth element, and 100 parts by mass of a main component satisfying x ≧ 0.2 and 0.05 ≦ α ≦ 0.3, and Mn as MnO ₂ It is preferable to contain 0.05-2.0 mass parts in conversion. In such a piezoelectric ceramic, Mn is less likely to be unevenly distributed in the grain boundary portion of the main phase of the bismuth layered compound, and the precipitation phase containing Mn can be prevented from welding the piezoelectric ceramic and the firing jig. Details of the reason why Mn is less likely to be unevenly distributed at the grain boundary are unknown, but it can take various valences on lattice defects created by substituting + trivalent elements in bismuth layered compounds with + trivalent rare earth elements. Since Mn is easy to enter, it is considered that Mn solid solution in the main phase of the bismuth layered compound is promoted and Mn hardly remains in the grain boundary part.

  Here, since x ≧ 0.2, the number of layers of the quasi-perovskite layer whose insulating properties deteriorate is changed from a crystal structure of three layers to a crystal structure including four or more quasi-perovskite layers. Improves insulation.

  Moreover, since α ≧ 0.05, the substitution amount of the rare earth element in the bismuth layered compound is sufficient to dissolve Mn, so that Mn is less likely to be unevenly distributed in the grain boundary portion. When α <0.05, the substitution amount of the rare earth element in the bismuth layered compound is not sufficient for solid solution of Mn, so that Mn is unevenly distributed in the grain boundary part. When α ≦ 0.3, a piezoelectric ceramic is obtained. When α> 0.3, the piezoelectric characteristics are very low, and the dielectric ceramic becomes simple.

Further, since the insulation of the piezoelectric ceramic deteriorates as the amount of Mn added increases, the amount of Mn added is considered to be 2 parts by weight or less with respect to 100 parts by weight of the bismuth layered compound as the main component in terms of MnO ₂ . If x ≧ 0.1 and α ≧ 0.05, the amount of Mn does not precipitate at the grain boundary portion of the bismuth layered compound phase, but mainly dissolves in the bismuth layered compound.

In addition, what is used as A should just be alkaline-earth metal ( _beta) (alkali metal _1/2 Bi1 _{/ 2} ) _1-beta (0 <= (beta) <= 1). That is, A may be only alkali metal, (alkali metal _1/2 Bi _1/2 ), or a combination of these at an arbitrary ratio. By using the same amount of alkali metal and Bi, they behave like divalent ions on average. Therefore, when an alkaline earth metal and (alkali metal _1/2 Bi _1/2 ) are mixed and used as A, the ratio may be arbitrary.

In the above composition formula, Mn is 0.05 to 2.0 parts by mass in terms of MnO ₂ with respect to 100 parts by mass of the main component satisfying n + 0.2 ≦ x ≦ n + 0.9 (n is an integer of 0 or more). By containing, a piezoelectric ceramic having a large absolute value of the piezoelectric constant can be obtained. This is because, by setting x to the above-mentioned range, in the bismuth layered compound, when the number of pseudo-perovskite layers in the bismuth layered compound is an odd number, the polarization axis is in the c-axis direction of the crystal lattice of the pseudo-perovskite layer. Occur. When the number of quasi-perovskite layers is a non-integer composition, the amount of polarization increases, and the amount of polarization increases particularly near the composition of x = n + 0.5. Therefore, when x is in the above-described range, the quasi-perovskite layer of the bismuth layered compound can be brought into a state in which the amount of polarization is large.

The increase in polarization of the above, which was expressed by the crystal portion adjacent the Bi ₂ O ₂ of the perovskite layer is distorted perovskite layer 1-3 layer worth adjacent at least Bi ₂ O ₂ Is believed to be distorted by Bi ₂ O ₂ . As the value of n increases, the portion of the pseudo-perovskite layer that is far away from Bi ₂ O ₂ increases, and the porcelain characteristics of the portion approach the characteristics of a porcelain having a normal perovskite structure. When n = 7 or less, further n = 5 or less, particularly n = 3 or less, the influence of the crystal distortion portion adjacent to Bi ₂ O ₂ in the pseudo-perovskite layer is large, and n + 0.2 ≦ x ≦ n + 0 .9 can increase the amount of polarization in particular.

  Note that the Curie temperature of the bismuth layered compound decreases as the value of x increases. From the viewpoint of only the value of the piezoelectric constant, since the proportion of the pseudo-perovskite layer increases as the value of x increases, the value of the piezoelectric constant tends to increase. However, a piezoelectric ceramic used in a high-temperature environment needs to have a high Curie temperature, and has a large absolute value of piezoelectric constant n + 0.2 ≦ x ≦ n + 0. A bismuth layered compound of 9 is preferred. The Curie temperature of the bismuth layered compound varies depending on the substance to be added, but x = 0 to 1 is about 600 to 400 ° C., x = 1 to 2 is about 500 to 300 ° C., x = 2 to 3 is 300 to 200 ° C. Degree.

Within the range of x = 0 to 1, 0.4 ≦ x ≦ 0.7, the Curie temperature is 400 ° C. or more, and the number of layers is mainly a mixture of three and four pseudo-perovskite layers. Therefore, as described above, the absolute value of the piezoelectric constant increases, and the piezoelectric d ₃₃ constant can be 17 pC / N or more.

Within the range of x = 1 to 2, 1.4 ≦ x ≦ 1.7, a Curie temperature of 300 ° C. or higher, and a state in which mainly four and five pseudo-perovskite layers are mixed. Therefore, as described above, the absolute value of the piezoelectric constant increases, and the piezoelectric d ₃₃ constant can be 21 pC / N or more.

The piezoelectric ceramic according to the present invention includes, for example, Bi ₂ O ₃ , TiO ₂ , MnCO ₃ , RE ₂ O ₃ , A1CO ₃ (A1 is an alkaline earth metal element), A2 ₂ CO ₃ (A2 is an alkali metal element) as a raw material. ) And the like, and oxides or salts of each element can be used. A raw material is not limited to this, You may use metal salts, such as carbonate and nitrate which produce | generate an oxide by baking.

The raw material containing Mn is preferably a powder having an average particle size distribution (D ₅₀ ) of 1 μm or less, and D ₉₀ is preferably 2 μm or less. This is because the raw material powder containing Mn having a large particle size cannot sufficiently diffuse and dissolve Mn in the surroundings through the calcination of the raw material and the firing process of the piezoelectric ceramic, which will be described later, and a part with a high content of Mn component is formed. This is because this part may become a crystal phase containing Mn. In order to further suppress the uneven distribution of Mn, it is more preferable that the raw material containing Mn has an average particle size distribution of 0.8 μm or less. Further, since MnO ₂ tends to leave a powder having a large particle size even after being pulverized, it is preferable to use MnCO ₃ as a raw material containing Mn.

When these raw materials are represented by the composition formula Bi ₄ Ti ₃ O ₁₂ · x (A _1-α RE _α ) TiO ₃ , A is an alkaline earth metal _β (alkali metal _1/2 Bi _1/2 ) _{1- β} , RE is a rare earth element, 100 parts by mass of the main component satisfying x ≧ 0.2, 0.05 ≦ α ≦ 0.3, 0 ≦ β ≦ 1, and Mn in an MnO ₂ conversion of 0. The mixture is weighed so as to have a composition containing 0.5 to 2.0 parts by mass, and pulverized so that the average particle size distribution (D ₅₀ ) after mixing and pulverization is in the range of 0.5 to 1 μm. The mixture is calcined at 1050 ° C., and the calcined powder is pulverized so that the average particle size distribution (D ₅₀ ) after mixing and pulverization is in the range of 0.5 to 1 μm. The powder thus obtained is molded into a predetermined shape by known press molding or the like, and baked in an oxidizing atmosphere such as the air at a temperature range of 1050 to 1250 ° C. for 2 to 5 hours. Is obtained.

  The piezoelectric ceramic of the present invention is most suitable as a piezoelectric ceramic for a pressure sensor as shown in FIGS. 1A and 1B, but other piezoelectric resonators, ultrasonic vibrators, ultrasonic motors, and acceleration sensors. It can be used for piezoelectric sensors such as knocking sensors and AE sensors, piezoelectric actuators, and the like.

  1A and 1B show a piezoelectric sensor which is a piezoelectric element of the present invention. This piezoelectric element is configured by forming electrodes 2, 3, 12, and 13 on both surfaces of the piezoelectric ceramics 1 and 11. The polarization is applied in the thickness direction (polarization direction P). These piezoelectric elements are not subjected to polishing after firing, and each surface has a burned surface, so that even when used as a piezoelectric sensor to which a pressure of 100 MPa or more is applied, the destruction caused by cracks and cracks caused by polishing is suppressed. can do.

  FIG. 1C shows a piezoelectric resonator (piezoelectric oscillator) which is a piezoelectric element of the present invention. The piezoelectric resonator is configured by forming electrodes 22 and 23 on a pair of opposing main surfaces of the piezoelectric ceramic 21 having the above-described composition, respectively.

  FIG. 1 (d) shows a longitudinal sectional view of a piezoelectric actuator which is a piezoelectric element of the present invention. In this piezoelectric actuator, an electrode (individual drive electrode) 32 and an electrode (common electrode) 33 are respectively formed on a pair of opposed main surfaces of the piezoelectric ceramic layer 31 made of the piezoelectric ceramic having the above composition. A diaphragm 35 is laminated on the main surface on which the electrode 33 is formed. The individual drive electrodes 32, the piezoelectric ceramic layer 31, the common electrode 33 and the diaphragm 35 constitute a plurality of displacement elements 37. The polarization of the piezoelectric ceramic layer 31 is performed on the entire piezoelectric ceramic layer 31 or a portion sandwiched between the individual drive electrode 32 and the common electrode 33. When a voltage is applied between the individual drive electrode 32 and the common electrode 33, the piezoelectric ceramic layer 31 is polarized. The layer 31 contracts or expands, and the displacement element 37 bends due to a dimensional difference from the diaphragm 35 to form a piezoelectric actuator.

  Although the material of the diaphragm 35 is not particularly limited, the piezoelectric ceramic layer 31 is substantially the same as the piezoelectric ceramic layer 31 of the present invention, so that the difference between the thermal expansion coefficient of the piezoelectric ceramic layer 31 and the thermal expansion coefficient of the diaphragm 35 is different. This reduces the number of cracks and improves the reliability. Moreover, since the piezoelectric ceramic layer 31, the common electrode 33, and the diaphragm 35 can be integrally fired, they can be produced at low cost.

First, Bi ₂ O ₃ , TiO ₂ , A1CO ₃ (A1 is an alkaline earth metal element: Ca, Ba, Sr), A2 ₂ CO ₃ (A2 is an alkali metal element: K, with a purity of 99.9% as a starting material. Na) and RE ₂ O ₃ (RE is a rare earth element: La, Tb, Sm, Dy, Y, Gd, Nd, Er, Yb, Lu, Eu), and the composition formula by molar ratio is Bi ₄ Ti ₃ O _12. When represented by x (A _1-α RE _α ) TiO ₃ , x, A, RE, and α represent MnCO ₂ powder in terms of MnO ₂ with respect to the main components shown in Table 1 and 100 parts by mass of the main components. 1 was weighed and mixed so as to be the mass part shown in 1.

The weighed raw material powder was put into a 500 ml polypot together with ZrO ₂ balls having a purity of 99.9% and ion-exchanged water, and mixed in a rotary mill for 16 hours.

The slurry after mixing was dried in the air, passed through # 40 mesh, and then calcined by holding at 950 ° C. for 3 hours in the air, and this synthetic powder was charged with 99.9% purity ZrO ₂ balls and ions. It put into a 500 ml polypot with exchange water, and grind | pulverized for 20 hours, and obtained evaluation powder.

  An appropriate amount of an organic binder is added to this powder, granulated, molded with a die press, and finally fired in air at 1050 ° C. to 1250 ° C. for 3 hours to obtain a cylindrical piezoelectric ceramic having a diameter of 6 mm and a thickness of 2 mm. It was. Firing was performed by placing it on a firing jig of stabilized zirconia. At this time, the evaluation of welding with one or more firing jigs among the 30 piezoelectric ceramics was “Yes”.

  The cross-section of the piezoelectric ceramic is mirror-polished, Mn element mapping at a magnification of 5000 times and SEM image are overlapped with EPMA of an electron microscope, and the grain interior and grain boundary part of the bismuth layered compound in the SEM image are compared by element mapping. When the boundary portion contains a large amount of Mn, that is, when the grain boundary portion includes a portion having a high element count, the presence of Mn in the grain boundary portion is determined to be “present”. In addition, the site | part with a high Mn count number was mainly observed in the triple point of the grain boundary of a bismuth layered compound.

  Ag electrodes were formed on both main surfaces (upper and lower surfaces of the cylinder) of the piezoelectric ceramic, and polarization treatment was performed at 200 ° C. to obtain a piezoelectric element.

For the piezoelectric element, the piezoelectric d ₃₃ constant was measured with a d ₃₃ meter, and IR was evaluated according to JIS-C2141. Furthermore, the piezoelectric element was placed in a thermostatic chamber, the capacitance was measured while changing the temperature, and the temperature at which the capacitance was maximum and maximum was taken as the Curie temperature. These results are shown in Table 1.

Sample No. outside the scope of the present invention. In No. 1, since Mn was not added, there was no welding with the firing jig. However, the piezoelectric ceramic was not sufficiently sintered, and the ceramic relative density of the piezoelectric ceramic added with 0.05 mass part or more of Mn was 90. The porcelain relative density was as low as about 80%, compared to the case of more than 50%, and even a little handling caused chipping.

Sample No. outside the scope of the present invention. In No. 2, since Mn was added, the piezoelectric ceramic was sufficiently sintered and the piezoelectric d ₃₃ constant was high, but uneven distribution of Mn was observed at the grain boundary portion, and therefore welding with the firing jig occurred. .

Sample No. In 3-6, 9-34, 37-41 and 43-51, the composition formula is represented by Bi ₄ Ti ₃ O ₁₂ · x (A _1-α RE _α ) TiO ₃ , and A is an alkaline earth metal _β ( Alkali metal _1/2 Bi _1/2 ) _1-β , RE is a rare earth element, and main component 100 satisfying x ≧ 0.2, 0.05 ≦ α ≦ 0.3, 0 ≦ β ≦ 1 Since it contains 0.05 to 2.0 parts by mass of Mn in terms of MnO ₂ , the piezoelectric d ₃₃ constant was as high as 15 pC / N or more, and IR was also as high as 3 GΩ or more.

Sample No. In 3-6, 9-13, 16-20, 22-34, 37-41, and 43-51, n + 0.2 ≦ x ≦ n + 0.9 (n is an integer of 0 or more) is satisfied. _{The 33} constant was as high as 16 pC / N or higher. Further, in each n to n + 1 in the range, the piezoelectric constant _{d 33} becomes higher in the range of n + 0.2 ≦ x ≦ n + 0.9.

  Sample No. In 3-6, 10-12, 25-34, 37-41, and 43-51, since 0.4 <= x <= 0.7 was satisfied, the Curie temperature became as high as 450 degreeC or more.

Sample No. Since 17 to 19 satisfied 1.4 ≦ x ≦ 1.7, the piezoelectric d ₃₃ constant was as high as 21 pC / N or more.

Moreover, when all the produced samples were analyzed by X-ray diffraction, a bismuth layered compound was recognized as the main phase. The bismuth layered compound has a crystal structure in which Bi ₂ O ₂ is inserted in a stack of perovskite structures.

  Furthermore, the composition analysis was performed for all the prepared samples using a fluorescent X-ray analyzer. As a result, the composition of the porcelain of each sample was the same as the prepared raw material composition.

(A) It is the schematic of the pressure sensor which is a piezoelectric element of one Embodiment of this invention. (B) It is the schematic of the pressure sensor which is a piezoelectric element of one Embodiment of this invention. (C) It is the schematic of the resonator which is a piezoelectric element of one Embodiment of this invention. (D) It is the schematic of the piezoelectric actuator which is a piezoelectric element of one Embodiment of this invention.

Explanation of symbols

1, 11, 21, 31 ... Piezoelectric ceramic 2, 3, 12, 13, 22, 23, 32, 33 ... Electrode 14 ... Hole 35 ... Diaphragm 37 ... Displacement element P ..Polarization direction

Claims (2)

The composition formula is represented by Bi ₄ Ti ₃ O ₁₂ × x (A _1−α RE _α ) TiO ₃ , A is an alkaline earth metal _β (alkali metal _1/2 Bi _1/2 ) _1−β , and RE Is a rare earth element, 100 parts by mass of the main component satisfying 1.4 ≦ x ≦ 1.7, 0.05 ≦ α ≦ 0.3, 0 ≦ β ≦ 1, and Mn in terms of MnO ₂ is 0.05. containing the 2.0 parts by weight, the bismuth layer compound with a main phase, the concentration of Mn to definitive in the grain boundary portion between the main phase, and equal to or less than the concentration of Mn in the main phase Piezoelectric ceramic.   A piezoelectric element, wherein a pair of electrodes are disposed opposite to each other on the surface and inside of the piezoelectric ceramic according to claim 1.

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