JP4903659B2 - 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, the elution of lead due to acid rain has been pointed out as a risk of 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, as a piezoelectric ceramic composition not containing lead, a material mainly composed of a bismuth layered compound whose composition formula is represented by SrBi ₄ Ti ₄ O ₁₅ has been proposed (see, for example, Patent Document 1).

Many materials mainly composed of bismuth layered compounds have a Curie temperature of 400 ° C. or higher. Such materials have high heat resistance and are exposed to high temperatures such as in an engine room. It may be applicable as a sensor element to be used.
JP 2000-313662 A

However, a piezoelectric ceramic mainly composed of a bismuth layered compound represented by the composition formula SrBi ₄ Ti ₄ O ₁₅ has a problem that the piezoelectric d constant is low. In order to improve this, it is mainly composed of a bismuth layered compound in which x = 1.5 when expressed by Bi ₄ Ti ₃ O ₁₂ · x [SrTiO ₃ ] in which the number of suspected perovskite layers is increased to a non-integer. In piezoelectric ceramics, although the piezoelectric d constant is large, the toughness of the piezoelectric ceramic is low, and the piezoelectric ceramic comes into contact with other piezoelectric ceramics and equipment in the manufacturing process, etc., the edge of the piezoelectric ceramic is chipped, or the thickness is 100 μm or less There was a problem that the thin piezoelectric ceramic was cracked.

  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 that are made of a bismuth layered compound that has a large piezoelectric d constant and is less likely to be damaged by processing.

The piezoelectric ceramic of the present invention is a piezoelectric ceramic whose main component is a bismuth layered compound, and is represented by a composition formula Bi ₄ Ti ₃ O ₁₂ · x [(Sr _a Ca _1−a ) _1−y Bi _y TiO ₃ ]. Mn is converted to MnO _{2 in} terms of MnO ₂ with respect to 100 parts by mass of the components satisfying 1.2 ≦ x ≦ 1.9, 0.05 ≦ y ≦ 0.3, and 0.4 ≦ a ≦ 0.6. It contains 05 to 2 parts by mass.

  The piezoelectric ceramic preferably satisfies 0.1 ≦ 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, the piezoelectric ceramic is composed of a bismuth layered compound as a main component, and has the composition formula Bi ₄ Ti ₃ O ₁₂ · x [(Sr _a Ca _1−a ) _1−y Bi _y TiO ₃ ]. , Mn is converted to MnO ₂ with respect to 100 parts by mass of the component that satisfies 1.2 ≦ x ≦ 1.9, 0.05 ≦ y ≦ 0.3, and 0.4 ≦ a ≦ 0.6. By containing 0.05 to 2 parts by mass, the piezoelectric d constant can be increased, the relative density of the piezoelectric ceramic is increased, and the fracture toughness value can be increased.

  The piezoelectric d constant can be increased by setting the amount of the composition that becomes the suspected perovskite layer of the bismuth layered compound to an amount corresponding to a non-integer number between 4 and 5. At this time, by replacing a part of Sr or Ca in the suspected perovskite layer to be increased by Bi, there is no deterioration of sinterability due to the increased suspected perovskite layer, and the sinterability of the piezoelectric ceramic is improved and densification is promoted. To do. Therefore, the fracture toughness of the porcelain is improved.

The piezoelectric ceramic is preferably 0.1 ≦ y ≦ 0.2 because the piezoelectric d ₃₃ constant can be further increased.

  According to the piezoelectric element of the present invention, the electrodes are provided on a pair of opposing surfaces of the piezoelectric ceramic substrate, so that the piezoelectric element is less likely to be chipped or cracked during the manufacturing process of the piezoelectric element. Therefore, defects due to them are reduced, and a piezoelectric element with a good yield can be obtained.

The piezoelectric ceramic according to the present invention is a piezoelectric ceramic whose main component is a bismuth layered compound, and is represented by the composition formula Bi ₄ Ti ₃ O ₁₂ · x [(Sr _a Ca _1−a ) _1−y Bi _y TiO ₃ ]. Mn is converted to MnO _{2 in} terms of MnO ₂ with respect to 100 parts by mass of the components satisfying 1.2 ≦ x ≦ 1.9, 0.05 ≦ y ≦ 0.3, and 0.4 ≦ a ≦ 0.6. It is important to contain 0.5 to 2 parts by mass.

  The bismuth layered compound has a structure in which bismuth layers and suspicious perovskite layers are alternately stacked, and research is progressing on the number of perovskite layers m (= 3 + x) included in the suspicious perovskite layer being an integer value. . When m is an integer, it is considered that if the value of m is large, the number m of quasi-perovskite layers in the crystal structure of the bismuth layered compound increases, so that the piezoelectric characteristics increase. Furthermore, when the number of pseudo-perovskite layers in the bismuth layered compound is an odd number, a polarization axis is generated in the c-axis direction of the crystal lattice of the pseudo-perovskite layer. In the case of a composition in which the number of quasi-perovskite layers is not an integer, the amount of polarization increases, and particularly in the vicinity of a composition in which x is a half integer, in particular, in the range of 1.2 ≦ x ≦ 1.9. The d constant increases.

  However, there was a tendency that sintering became difficult as the number of layers increased. And, when the firing temperature is increased to advance the sintering, a heterogeneous phase such as a compound of Bi and Mn is precipitated, and the porcelain density is increased, but the insulating property is lowered due to the precipitated heterogeneous phase, The polarization process cannot be performed sufficiently, and the piezoelectric d constant decreases. Therefore, the height of the piezoelectric d constant is not compatible with the yield of manufacturing a thin-layer piezoelectric ceramic.

  Therefore, by replacing the divalent ion of the A-site element of the bismuth layered compound with Bi, that is, by replacing a part of Sr or Ca in the suspected perovskite layer with Bi, it is difficult to sinter the bismuth layered compound. Sinterability is improved and densification is promoted. This is thought to be because the diffusion of A-site atoms occurs early due to the formation of vacancies at the A-site by substitution. This densification makes it difficult to be destroyed during the processing of the piezoelectric ceramic.

  Further, by setting a to 0.4 ≦ a ≦ 0.6, the Curie temperature can be increased, and the piezoelectric ceramic can be used up to a higher temperature.

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. When the content of Mn 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, if the content of Mn is more than 2.5 parts by mass in terms of MnO ₂ , the volume specific resistance becomes low and polarization becomes impossible.

The main component of the piezoelectric ceramic of the present invention is represented by the composition formula Bi ₄ Ti ₃ O ₁₂ · x [(Sr _a Ca _1-a ) _1-y Bi _y TiO ₃ ] as a composition formula. 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 piezoelectric ceramic of the present invention, the above composition formula and MnO ₂ occupy 99% or more, and the other composition is less than 1%, more preferably less than 0.5%.

  In the present invention, a piezoelectric ceramic composed of a bismuth layered compound is an XRD (X-Ray Diffraction: X-ray diffraction) in which the crystal phase peak other than the main peak of the bismuth layered compound is 5% or less in intensity ratio. Or TEM (Transmission Electron Microscopy: Transmission Electron Microscope) is observed at a magnification of 10,000, and crystal particles that are bismuth layered compounds are identified by electron diffraction. It occupies more than%.

In the piezoelectric ceramic having the composition of the present invention, for example, various oxides composed of SrO, CaO, Bi ₂ O ₃ , MnO ₂ , and TiO ₂ or salts thereof can be used as raw materials. 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 addition, as a piezoelectric sensor element, in order to obtain a pressure sensor capable of stable measurement even at a high temperature of 200 ° C., 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, an SrO powder having a purity of 99.9%, a CaO powder, a Bi ₂ O ₃ powder, and a TiO ₂ powder as a starting material, a composition formula Bi ₄ Ti ₃ O ₁₂ · x [(Sr _a Ca _1-a ) by molar ratio. _1-y Bi _y TiO ₃ ], x, y, a are the main components in the amounts shown in Table 1, and 100 parts by mass of the main components, and the parts by mass of MnO ₂ powder shown in Table 1 Weighed and mixed so that

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 air at 1130 ° C. or 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 1.0 mm were 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 measures the piezoelectric d ₃₃ constant with a d ₃₃ meter, and further puts the piezoelectric element in a thermostatic bath, measures the capacitance while changing the temperature, and the capacitance is maximum and maximum. The temperature at which this was achieved was taken as the Curie temperature. Subsequently, the volume resistivity was evaluated according to 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 lapped with No. 2000 until the thickness became 0.1 mm. 100 laps were processed, and the yield was calculated assuming that no cracks or chips were found. The results are shown in Table 1.

As is apparent from Table 1, sample nos. 15-22, 26-30, 34, 35 and 38-42 could be fired at 1130 ° C., and the yield of lapping was as high as 90% or higher. _Also, as high as _{d 33} constant even 22pC / N or more. Further, the Curie temperature was as high as 430 ° C. or higher.

In particular, sample nos. In 15-22, 27, 28, 34, 35 and 38-42, the piezoelectric d ₃₃ constant was as high as 24 pC / N or more because 0.1 ≦ y ≦ 0.2.

On the other hand, sample no. In 5 to 7 and 23, since x exceeds 1, the piezoelectric d ₃₃ constant is increased at a firing temperature of 1030 ° C., but the relative density is lower than 90%, and the yield of lapping is 90. It was low with less than%. Sample No. Sample No. 5 outside the scope of the present invention with the same composition as 5-7 and a firing temperature of 1250 ° C. 8-10, the relative density of volume resistivity is lowered by heterophase precipitation that contains manganese and became 90% or more of bismuth, polarization is not performed sufficiently, the piezoelectric constant d ₃₃ was lower.

In addition, the sample no. No. 31 has a piezoelectric d ₃₃ constant as low as 19 pC / N.

In addition, the sample No. outside the scope of the present invention to which no MnO ₂ was added. In 37, 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. 43 was polarized but could not be polarized.

As a result of analysis by X-ray diffraction, sample no. 13 is a bismuth layered compound of m = 4, No. 13 In No. 23, a bismuth layered compound of m = 5 was recognized as the 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)

When the main component is a piezoelectric ceramic composed of a bismuth layered compound, and expressed as a composition formula Bi ₄ Ti ₃ O ₁₂ · x [(Sr _a Ca _1−a ) _1−y Bi _y TiO ₃ ], 1.2 ≦ Mn is contained in an amount of 0.05 to ₂ parts by mass in terms of MnO ₂ with respect to 100 parts by mass of the components satisfying x ≦ 1.9, 0.05 ≦ y ≦ 0.3, and 0.4 ≦ a ≦ 0.6. A piezoelectric ceramic characterized by that. 2. The piezoelectric ceramic according to claim 1, wherein 0.1 ≦ 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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