JP5219421B2 - 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, a resonator or a pressure sensor element has high piezoelectricity, for example, a PZT (lead zirconate titanate) -based material or a PT (lead titanate) -based material capable of obtaining a large generated charge with respect to a large P / V or pressure. It was used. However, since PZT-based materials 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 may be eluted by acid rain, resulting in environmental pollution. Therefore, high expectations are placed on piezoelectric materials that do not contain lead.

  In addition, since PZT materials and PT 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. Due to the fact that the piezoelectric d constant at 200.degree. 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, a material mainly composed of a bismuth layered compound has been proposed as a piezoelectric ceramic composition containing no lead (see, 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.
JP2002-167276

  However, conventional piezoelectric ceramics mainly composed of lead-free bismuth layered compounds have low toughness of piezoelectric ceramics, and in the manufacturing process, etc., the piezoelectric ceramic contacts other piezoelectric ceramics and equipment, and the edge of the piezoelectric ceramic is There was a problem of chipping or cracking in a thin piezoelectric ceramic having a thickness of 100 μm or less.

  Further, when a piezoelectric ceramic is used as a pressure sensor element, since pressure is applied to the piezoelectric ceramic, there is a problem that mechanical reliability is inferior when the relative density is low. Furthermore, when a piezoelectric ceramic is used as a resonator, for example, when element processing such as dicing cut is performed, if the relative density is low, chipping occurs on the processed surface or edge of the piezoelectric ceramic, causing ripples. there were.

  Accordingly, an object of the present invention is to provide a piezoelectric ceramic and a piezoelectric element made of a bismuth layered compound that hardly breaks down by processing.

The piezoelectric ceramic of the present invention is composed of a bismuth layered compound whose main component is formed by firing raw materials each containing M ₂ O (M is an alkali metal element) Bi ₂ O ₃ , MnO ₂ and TiO ₂ or a salt thereof. a piezoelectric ceramic comprising, 1 in M of the raw material, the molar ratio of Bi and Ti, the chemical formula _{Bi 4 Ti 3 O 12 · x} [(Bi 1/2 M 1/2) 1-y Bi y TiO 3] 0.2 ≦ x ≦ 1.9 and 0 ≦ y ≦ 0.3 , and the mass ratio of Mn of the raw material is 100 parts by mass expressed by the chemical formula, and Mn is converted to MnO ₂ . It contains 0.05 to 2.0 parts by mass.

  Moreover, it is preferable that the said piezoelectric ceramic is 0.05 <= y <= 0.2.

  The piezoelectric element of the present invention is characterized in that electrodes are provided on a pair of opposing surfaces of a base body made of the piezoelectric ceramic.

According to the piezoelectric ceramic of the present invention, M ₂ O (M is an alkali metal element) Bi ₂ O ₃ , MnO ₂ and TiO _2, or a main component formed by firing a raw material each containing a salt thereof, is bismuth layered A piezoelectric ceramic made of a compound, wherein the molar ratio of M, Bi and Ti of the raw material is expressed by the chemical formula Bi ₄ Ti ₃ O ₁₂ · x [(Bi _1/2 M _1/2 ) _1-y Bi _y TiO ₃ ]. in the range of 1.2 ≦ x ≦ 1.9,0 ≦ y ≦ 0.3, the mass ratio of Mn of the feedstock relative to the amount 100 mass parts expressed by the formula, MnO ₂ and Mn By containing 0.05 to 2.0 parts by mass in terms of conversion, the relative density of the piezoelectric ceramic is increased, and the fracture toughness value can be increased.

  By substituting bismuth and alkali metal elements that are divalent on average instead of divalent ions of the A-site element of the bismuth layered compound, the sinterability of the hardly sinterable bismuth layered compound is improved and densified. Promotes. Further, by satisfying 1.2 ≦ x ≦ 1.9, the sinterability is further improved and the densification is promoted. Therefore, the fracture toughness of the porcelain is improved.

The piezoelectric ceramic is preferably 0.05 ≦ y ≦ 0.2 because the piezoelectric d ₃₃ constant can be increased.

  According to the piezoelectric element of the present invention, the piezoelectric element is provided with electrodes on a pair of opposing surfaces of the base made of the piezoelectric ceramic, so that the piezoelectric element is less likely to be chipped or cracked during the process. Therefore, an inexpensive piezoelectric element can be obtained.

The piezoelectric ceramic according to the present invention is a piezoelectric ceramic mainly composed of a bismuth layered compound, and the composition formula is Bi ₄ Ti ₃ O ₁₂ × [(Bi _1/2 M _1/2 ) _1-y Bi _y TiO _3. M is an alkali metal element, and Mn is converted to MnO _{2 in} terms of MnO ₂ with respect to 100 parts by mass of 1.2 ≦ x ≦ 1.9 and 0 ≦ y ≦ 0.3. It is important to contain 2.0 parts by mass.

  As for the bismuth layered compound, researches are mainly made for those in which x is an integer. When x is an integer, it is considered that when the value of x is large, the number of quasi-perovskite layers in the crystal structure of the bismuth layered compound increases, so that the piezoelectric characteristics increase. However, there was a tendency that sintering became difficult as the number of layers increased. Increasing the firing temperature may change the piezoelectric characteristics due to the composition of the piezoelectric ceramic due to the evaporation of bismuth and reaction with the firing jig. The yield of porcelain production has not been improved sufficiently.

  Therefore, the sinterability of the hardly sinterable bismuth layered compound is improved by substituting bismuth and alkali metal elements that are divalent on average instead of the divalent ion of the A site element of the bismuth layered compound. Densification is promoted. This is presumably because the alkali metal element easily diffuses during firing, and thus the sinterability increases. Further, by setting 1.2 ≦ x ≦ 1.9, the sinterability is further improved and the densification is promoted, and therefore, it is difficult to be destroyed during the processing of the piezoelectric ceramic.

The coefficient y is preferably 0.05 ≦ y ≦ 0.2 because the piezoelectric d ₃₃ constant of the piezoelectric ceramic can be increased.

Furthermore, when the content of Mn is 0.05 parts by mass or more in terms of MnO _{2 with} respect to 100 parts by mass of the above-described component, it is easy to sinter even in this material system that is a plate-like crystal, and the fine porcelain Is obtained. If the Mn content is less than 0.05 parts by mass in terms of MnO ₂ , the relative density is lowered and the porcelain strength is extremely lowered. On the other hand, when the content of Mn is more than 2.05 parts by mass in terms of MnO ₂ , IR becomes low and polarization becomes impossible.

The main component of the piezoelectric ceramic of the present invention is represented by _Bi 4 _Ti 3 _O 12 _· x a composition formula _{[(Bi 1/2 M 1/2) 1} -y Bi y TiO 3], as the predominant crystal phase Is made of a bismuth layered compound. That is, the piezoelectric ceramic of the present _invention, in the ^{_{(Bi 2 O 2) 2+ (}} α m-1 β m O 3m + 1) General formula bismuth layer compound Kakiarawasa with ^2, the alpha sites and beta sites and oxygen Site It is considered that the structure is a bismuth layered compound in which m = 4 and m = 5 are mixed with some defects, and Mn is partly dissolved. In the porcelain to which Mn is added, Mn is solid-solved in the main crystal phase, but may partially precipitate at the grain boundary as a crystal of the Mn compound. As other crystal phases, there may be a pyrochlore phase, a perovskite phase, and a bismuth layered compound having a different structure.

In the piezoelectric ceramic according to the present invention, Zr or the like may be mixed from the ZrO ₂ ball at the time of pulverization.

  In the present invention, a piezoelectric ceramic made of a bismuth layered compound is a bismuth layered compound by observing a cross section at 2000 times with a scanning electron microscope (SEM) to identify crystal particles that are a bismuth layered compound. The crystal grains occupy 90 area% or more.

The piezoelectric ceramic having the composition of the present invention uses, for example, various oxides or salts thereof made of Li ₂ CO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Bi ₂ O ₃ , MnO ₂ , and TiO ₂ as raw materials. be able to. 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.

These raw materials are weighed so as to have the above-described composition, pulverized so that the average particle size distribution (D ₅₀ ) after mixing is in the range of 0.3 to 1 μm, and this mixture is calcined at 850 to 1000 ° C. Then, pulverization is performed so that the average particle size distribution (D ₅₀ ) after calcination is in the range of 0.3 to 1 μm, and a predetermined organic binder is added again, followed by wet mixing and granulation.

  The powder thus obtained is molded into a predetermined shape by a known press molding or the like, and calcined at a temperature range of 1000 to 1250 ° C. for 2 to 5 hours in an oxidizing atmosphere such as the atmosphere to obtain the composition of the present invention. The piezoelectric ceramic which has is obtained.

  FIG. 1A shows a piezoelectric sensor element which is a piezoelectric element of the present invention. This piezoelectric sensor is configured by forming electrodes 2 and 3 on a pair of opposing main surfaces of a piezoelectric substrate 1 made of a piezoelectric ceramic having the above-described composition. Polarization is performed in a direction perpendicular to the main surface. In such a pressure sensor, an electric charge is generated on each main surface due to the pressure applied between the main surfaces, and the pressure applied between the main surfaces can be measured. And since the piezoelectric substrate 1 is of the above-mentioned composition, it becomes a piezoelectric sensor element that is not easily destroyed by mechanical stress.

  In order to obtain a pressure sensor capable of stable measurement even at a high temperature of 200 ° C. as a piezoelectric sensor element, studies using single crystals such as langasite and quartz have been made. In the case of these single crystals, there is a problem that the piezoelectric d constant is small, chipping is likely to occur during processing, and the single crystal is easily cracked. Further, the manufacturing cost of the single crystal is extremely high. Porcelain can be manufactured inexpensively without such workability problems.

  FIG. 1B shows a piezoelectric resonator (piezoelectric oscillator) which is a piezoelectric element of the present invention. This piezoelectric resonator is configured by forming electrodes 22 and 23 on a pair of opposing main surfaces of a piezoelectric substrate 21 made of a piezoelectric ceramic having the above composition, respectively. In such a piezoelectric resonator, by using a piezoelectric ceramic having the above-described composition, chipping due to processing can be greatly suppressed, and further, a molded body is produced and fired to a desired shape by a molding die. Therefore, the piezoelectric element can be obtained, and phase shift distortion due to spurious vibration does not occur between the resonance frequency and anti-resonance frequency due to chipping (missing of the ceramic edge for the resonator), and the phase shift condition is satisfied. Therefore, oscillation does not occur and stable oscillation can be obtained.

First, as a starting material, Li ₂ CO ₃ powder, Na ₂ CO ₃ powder, K ₂ CO ₃ powder, Bi ₂ O ₃ powder, and TiO ₂ powder having a purity of 99.9% are represented by a molar composition of Bi ₄ Ti _3. When O ₁₂ · x [(Bi _1/2 M _1/2 ) _1-y Bi _y TiO ₃ ], M, x, and y are main components having the components and amounts shown in Table 1, and this main component 100 The MnO ₂ powder was weighed and mixed so as to be the mass part shown in Table 1 with respect to the mass part.

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 mixed slurry is dried in the air, passed through a # 40 mesh, and then calcined at 950 ° C. for 3 hours in the air, and this synthetic powder is ion-exchanged with a ZrO ₂ ball having a purity of 99.9%. It put into a 500 ml polypot with water, and it 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 mold press at a pressure of 150 MPa, and finally fired in the air at 1050 ° C. to 1250 ° C. for 3 hours. A circle having a diameter of 6 mm and a thickness of 2.5 mm A columnar piezoelectric constant measuring piezoelectric ceramic and a plate-shaped piezoelectric ceramic for evaluation of lapping processing having a length of 25 mm, a width of 38 mm, and a thickness of 0.5 mm were obtained.

Similarly, sample No. As 20 and 21, a piezoelectric ceramic was produced with a raw material represented by the composition formula Bi ₄ Ti ₃ O ₁₂ · x [SrTiO ₃ ].

  The minimum firing temperature described in Table 1 means the minimum temperature at which a suitable porcelain can be obtained, and firing is performed at a firing temperature with the highest relative porcelain density in the range of firing temperatures from 1050 ° C to 1250 ° C. This is the lowest temperature among the firing temperatures at which a piezoelectric ceramic having a relative density equivalent to that of the produced piezoelectric ceramic is obtained.

After the piezoelectric constant measuring piezoelectric ceramic was polished to a thickness of 2 mm, Ag electrodes were formed on both main surfaces (the upper and lower surfaces of the cylinder), and polarization treatment was performed at 200 ° C. to obtain a piezoelectric constant measuring piezoelectric element. The obtained piezoelectric constant measuring element measured the piezoelectric d ₃₃ constant with a d ₃₃ meter, and evaluated IR according to JIS-C2141. Moreover, IR was evaluated based on JIS-C2141.

  Furthermore, the porcelain relative density was calculated by dividing the bulk density measured according to JIS-R2205 by the true density. The true density was determined by measuring the density of the porcelain without pores in the porcelain, using a mortar to pulverize the piezoelectric ceramic to an average particle size of about 3 μm, and measuring the result using the pycnometer method.

The piezoelectric ceramic for lapping evaluation was No. 2000 and lapping was performed until the thickness became 0.1 mm. A lapping process was performed for 100 pieces, and the yield was calculated assuming that there were no cracks or chips as good products. The results are shown in Table 1.

As is apparent from Table 1, sample nos. 6-13, 17, 19, 22-27, 30, 31 and 33-37 could be fired at 1180 ° C., and the yield of lapping was as high as 90% or higher. _Also, as high as _{d 33} constant is 20 pC / N or more.

In particular, sample nos. 22-26, _{d 33} constant is as high as 26PC / N or more by a 0.05 ≦ y ≦ 0.2.

  On the other hand, the sample No. x is outside the range of the present invention. 1 to 5, 14 to 16, 18 and 20, although the relative density was as high as 99%, the yield of lapping was less than 90% and the yield was low.

Also, outside of the sample No.28 and 29 of the present invention which is a y> _0.3, became constant _{d 33} is low than 20 pC / N.

In addition, No. 1 outside the scope of the present invention represented by the composition formula Bi ₄ Ti ₃ O ₁₂ × x [SrTiO ₃ ]. Since the sample of 21 was not substituted with divalent ions (Bi _1/2 M _1/2 ), it sintered only at a relative density of 96% even at a firing temperature of 1250 ° C., and the yield of lapping was also high. It was low.

In addition, the sample No. outside the scope of the present invention to which no MnO ₂ was added. In 32, the porcelain relative density was not sufficiently densified as 89%. Sample No. ₂ containing 2.5 parts by mass of MnO _{2 was} added. No. 38 was polarized, but could not be polarized.

As a result of analysis by X-ray diffraction, sample no. 4 is a bismuth layered compound of m = 4, No. 4 As for No. 14, the bismuth layered compound of m = 5 was recognized as a main crystal phase. The bismuth layered compound has a crystal structure in which Bi ₂ O ₂ is inserted in a stack of perovskite structures. The number of units having a perovskite structure sandwiched between Bi ₂ O ₂ layers is m. From this, it can be considered that the perovskite compound is incorporated into a bismuth layered compound having m = 4 and has crystals of m = 5. The sample of the present invention shows a structure between the two structures by X-ray diffraction, and the piezoelectric ceramic of the present invention is considered to have a structure of m = 5 and a structure of m = 4. And it is thought that it is a bismuth layered compound in which Mn is partly dissolved in these structures. Moreover, the cross section of each sample was observed and the bismuth layered compound occupied 90 area% or more.

  In addition, the composition of the sample prepared in the example was analyzed with 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) is the schematic of the pressure sensor element which is a piezoelectric element of this invention, (b) is the schematic of the resonator for 8 MHz which is a piezoelectric element of this invention.

Explanation of symbols

1, 21 ... Piezoelectric substrate (piezoelectric ceramic)
2, 3, 22, 23 ... Electrode P ... Polarization direction

Claims (3)

A piezoelectric ceramic comprising a bismuth layered compound as a main component formed by firing raw materials each containing M ₂ O (M is an alkali metal element) Bi ₂ O ₃ , MnO ₂ and TiO ₂ or a salt thereof . the raw material M, the molar ratio of Bi and Ti, the chemical formula _{Bi 4 Ti 3 O 12 · x} [(Bi 1/2 M 1/2) 1-y Bi y TiO 3] in 1.2 ≦ x ≦ 1. 9, 0 ≦ y ≦ 0.3 , and the mass ratio of Mn of the raw material is 0.05 to 2.0 in terms of MnO ₂ with respect to 100 parts by mass of the amount represented by the chemical formula. piezoelectric ceramic, characterized in parts by der Rukoto.   The piezoelectric ceramic according to claim 1, wherein 0.05 ≦ y ≦ 0.2.   3. A piezoelectric element comprising electrodes on a pair of opposing surfaces of a substrate comprising the piezoelectric ceramic according to claim 1 or 2.

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