JP2009096688A - Piezoelectric porcelain composition and resonator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric porcelain composition capable of achieving good temperature characteristics of oscillation frequency F<SB>0</SB>even when used in a resonator utilizing a third harmonic wave mode of thickness longitudinal vibration. <P>SOLUTION: The piezoelectric porcelain composition has a tetragonal perovskite crystal structure and has a length of a-axis of the crystal lattice of the perovskite crystal structure within the range of 3.91 to 4.02 Å. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piezoelectric ceramic composition and an oscillator.

  A piezoelectric ceramic composition has a piezoelectric effect that causes electrical polarization when subjected to pressure from the outside, and an inverse piezoelectric effect that causes distortion when an electric field is applied from the outside, so that mutual conversion between electrical energy and mechanical energy is achieved. It is used as a material for performing. Such piezoelectric ceramic compositions are used in various products such as resonators, filters, sensors, actuators, ignition elements or ultrasonic motors.

For example, as a piezoelectric ceramic composition used for a ceramic filter or the like using a third harmonic of thickness longitudinal vibration, Mn and Cr are added to a lead titanate system in which a part of Pb of PbTiO ₃ is replaced with La. There _{Pb 1-3y / 2 La y TiO 3} + z · composition represented by _{{(1-x) MnO 2} + (x / 2) · Cr 2 O 3} ( however, 0 <x <1,0 <z ≦ A piezoelectric ceramic composition characterized in that it is 5 wt%) is known (Patent Document 1).
JP-A-5-139824

In recent years, in an oscillation circuit using an oscillator including a piezoelectric element, the temperature characteristic of the oscillation frequency F ₀ is good in order to correspond to a product that requires a narrow tolerance of the oscillation frequency F ₀ (unit: Hz). It is requested. “The temperature characteristic of the oscillation frequency F ₀ is good” means that when the temperature of the resonator changes, the ratio of the change amount of the oscillation frequency F _{0 to} the temperature change amount is small, and the oscillation frequency against the temperature change. It means that _F0 is stable.

However, in the case of an oscillator that uses the third harmonic of the thickness longitudinal vibration (third harmonic mode of the thickness longitudinal vibration), the frequency band used is high compared to an oscillator that uses the bending vibration mode. in the conventional piezoelectric ceramic compositions, which can be fully satisfactory in terms of the temperature characteristic of the oscillation frequency F ₀ was not obtained. An oscillator that uses the third harmonic of the thickness longitudinal vibration can be applied to, for example, a resonator that is an element that generates a reference clock for controlling a microcomputer, and is also intended to replace an expensive crystal resonator. There is a need for a piezoelectric ceramic composition that exhibits sufficient performance when used in an oscillator that uses the third harmonic of thickness longitudinal vibration.

Therefore, the present invention provides a piezoelectric ceramic composition that makes it possible to obtain good temperature characteristics of the oscillation frequency F ₀ even when used in an oscillator that uses the third harmonic mode of thickness longitudinal vibration. Another object is to provide an oscillator using the piezoelectric ceramic composition.

  The piezoelectric ceramic composition of the present invention has a tetragonal perovskite crystal structure. In the piezoelectric ceramic composition of the present invention, the length of the a-axis (lattice constant in the a-axis direction) in the crystal lattice of the perovskite crystal structure is 3.91 to 4.02 angstroms.

  In the present invention, since the piezoelectric ceramic composition has a tetragonal perovskite crystal structure, the length of the a-axis and the length of the b-axis (lattice constant in the b-axis direction) in the crystal lattice are equal. Therefore, in the present invention, the length of the b-axis in the crystal lattice is also 3.91 to 4.02 angstroms.

  The oscillator of the present invention includes a piezoelectric element made of the piezoelectric ceramic composition of the present invention.

In the resonator according to the present invention, since the piezoelectric element has the perovskite crystal structure and the piezoelectric ceramic composition has an a-axis length of 3.91 to 4.02 angstroms in the crystal lattice, Even when used as an oscillator utilizing the third harmonic mode of longitudinal vibration, good temperature characteristics of the oscillation frequency F ₀ can be obtained.

The piezoelectric ceramic composition of the present invention is
_{(Pb α Ln β) (Ti} 1- (x + y + z) Zr x Mn y Nb z) O 3
[Wherein, Ln represents at least one selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. ]
0.91 ≦ α ≦ 1.00, 0 <β ≦ 0.08, 0.125 ≦ x ≦ 0.300, 0.020 ≦ y ≦ 0.050, and 0. It is preferable to satisfy 040 ≦ z ≦ 0.070. Thereby, the length of the a-axis in the crystal lattice of the perovskite crystal structure can be surely set to 3.91 to 4.02 angstroms.

According to the present invention, there is provided a piezoelectric magnetic composition that makes it possible to obtain a favorable temperature characteristic of the oscillation frequency F ₀ even when used in an oscillator that uses the third harmonic mode of thickness longitudinal vibration. Provided. In addition, since the piezoelectric ceramic composition of the present invention has a high Curie temperature, when used as a piezoelectric element of a surface-mount type oscillator, an oscillator with little deterioration in piezoelectric characteristics even when passed through solder reflow Can be obtained.

  Hereinafter, preferred embodiments of an oscillator using the piezoelectric ceramic composition of the present invention will be described with reference to the drawings as appropriate. However, the present invention is not limited to the following embodiments.

  FIG. 1 is a perspective view showing an embodiment of an oscillator, and FIG. 2 is a cross-sectional view taken along the line II-II in FIG. 1 and 2 includes a rectangular parallelepiped piezoelectric element 2 and a pair of vibrating electrodes 3 facing each other with the piezoelectric element 2 interposed therebetween. One vibration electrode 3 is formed at the center of the upper surface of the piezoelectric element 2, and another vibration electrode 3 is formed at the center of the lower surface of the piezoelectric element 2. The piezoelectric element 2 is made of the piezoelectric ceramic composition of the present embodiment. The vibrating electrode 3 is made of a conductive material such as Ag.

  The size of the piezoelectric element 2 may be an appropriate size depending on the application, and is, for example, about 1.0 to 7.0 mm in length, 0.5 to 7.0 mm in width, and about 100 to 300 μm in thickness. The shape of the vibrating electrode 3 is usually circular, and its dimensions are, for example, a diameter of 0.5 to 3.0 mm and a thickness of about 0.5 to 5 μm.

  The piezoelectric ceramic composition has a tetragonal perovskite crystal structure at room temperature (about 15 to 35 ° C.). The length of the a axis in the crystal lattice of this perovskite crystal structure is 3.91 to 4.02 angstroms.

In this embodiment, since the piezoelectric element 2 included in the oscillator 1 is formed from a piezoelectric ceramic composition having the length of the a-axis in the specific range, the oscillator 1 has a third harmonic mode of thickness longitudinal vibration. Even when the oscillator to be used is used in an oscillation circuit, a favorable temperature characteristic of the oscillation frequency F ₀ is achieved. In other words, in this embodiment, the rate of change RF ₀ (unit:%) of the oscillation frequency F ₀ with respect to the temperature change can be reduced. In this embodiment, the Curie temperature of the piezoelectric ceramic composition can be set to a desired value. The change rate RF ₀ is defined by the following mathematical formula (1) when the temperature of the oscillator 1 changes from the reference temperature T ₀ (unit: ° C.) to an arbitrary temperature T (unit: ° C.).
RF ₀ = {F ₀ (T) −F ₀ (T ₀ )} / F ₀ (T ₀ ) × 100 (1)
In Formula (1), F ₀ (T ₀ ) is the oscillation frequency F ₀ when the temperature of the oscillator 1 is a reference temperature T ₀ (for example, 25 ° C.), and F ₀ (T) is This is the oscillation frequency F ₀ when the temperature of the oscillator 1 is the temperature T.

By the way, the frequency temperature characteristic of a crystal conventionally used as an oscillator changes depending on the cut angle, and when the change rate of the oscillation frequency is plotted against temperature for an oscillator using a crystal, a quadratic curve or a cubic It is generally known that it can be approximated by a curve (refer to pages 119 to 121 of the general technology publication “Latest vibrator / resonator / filter 86th edition”). As in the case of the resonator using this crystal, also in the resonator 1 including the piezoelectric element 2 made of the piezoelectric ceramic composition of the present embodiment, the rate of change RF ₀ of the oscillation frequency F ₀ with respect to the temperature change is expressed by the following formula: It can be approximated by a quadratic curve (quadratic function) of the temperature T of the oscillator 1 represented by (2).
RF ₀ (T) = aT ² + bT + c (a, b, and c are real numbers, respectively) Expression (2)
Here, a value 2a obtained by doubling the coefficient a in Expression (2) is defined as the curvature of the change rate RF ₀ (T). According to the knowledge of the present inventors, in the resonator 1, since the length of the a axis in the crystal lattice of the piezoelectric ceramic composition is 3.91 to 4.02 angstroms, the rate of change RF ₀ (T) is high. The curvature 2a can be made smaller than before. Here, the change amount ΔRF ₀ of the change rate RF ₀ (T) with respect to the temperature change amount ΔT of the oscillator 1 is expressed by the following equation (3) calculated from the above equation (2).
_{ΔRF 0 = RF 0 (T +} ΔT) -RF 0 (T) = 2a × (ΔT × T + (ΔT) 2/2) + bΔT ··· Equation (3)
As apparent from the above equation (3), in the present embodiment, the amount of change ΔRF ₀ of the change rate RF ₀ with respect to the temperature change amount ΔT of the oscillator 1 is reduced by reducing the curvature 2a of the change rate RF ₀ (T). Can be reduced. In other words, the rate of change RF ₀ of the oscillation frequency F ₀ can be stabilized with respect to the temperature change of the oscillator 1.

Further, if the curvature 2a is small, the variation of the rate of change RF ₀ due to variations in the composition of the piezoelectric ceramic composition in the manufacturing process of the oscillator 1 and the process conditions such as firing becomes small, so the rate of change RF of the oscillator 1 _It is easy to fit ₀ within the desired narrow tolerance (product specifications). That is, in the manufacture of the oscillator 1, the control range of the composition of the piezoelectric ceramic composition and the process conditions can be afforded, and the yield can be improved.

The oscillator can be applied to, for example, a resonator that is an element that generates a reference clock for controlling a microcomputer. Conventionally, a crystal oscillator has been used as a resonator. However, since a crystal oscillator is expensive, it is desired to use an oscillator including an inexpensive piezoelectric element as a resonator from the viewpoint of substituting this crystal oscillator. As the microcomputer control resonator, the tolerance of the oscillation frequency F ₀ is narrow and has an absolute value of the rate of change RF ₀ of the oscillation frequency F ₀ of 0.1% or less, more preferably 0.05% or less performance An oscillator is required. Further, the smaller the absolute value of the curvature 2a of the rate of change RF ₀ is, the easier it is to make the absolute value of RF ₀ smaller. Therefore, the absolute value of the curvature 2a of the rate of change RF ₀ is 20. It is desirable to make it 0 or less. This is because the value of the curvature 2a is a factor that is almost determined only by the composition and is easy to control in manufacturing, whereas the value of the rate of change RF ₀ varies not only in the composition but also in the manufacturing conditions such as the firing conditions and electrode formation. This is because it is difficult to control. In other words, the greater the absolute value of the curvature 2a, the higher the possibility that the rate of change RF ₀ will fluctuate due to manufacturing causes and deviate from the product standard. For the above reasons, the oscillator 1 of the present embodiment, the tolerance of the oscillation frequency _{F 0} is narrow, the absolute value of the rate of change RF ₀ of the oscillation frequency _{F 0} of 0.1 or less, more preferably 0.05% with or less, the absolute value of the curvature 2a of the change rate RF ₀ is preferably not 20.0 or less. Such an oscillator 1 is suitable as an oscillator for an oscillation circuit for a personal computer.

The piezoelectric ceramic composition has a composition represented by the following chemical formula (1).
_{(Pb α Ln β) (Ti} 1- (x + y + z) Zr x Mn y Nb z) O 3 ··· formula (1)
In the formula (1), Ln is a lanthanoid element and is at least selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. 1 type is represented. Among these lanthanoid elements, Ln is particularly preferably at least one element selected from La, Pr, Ho, Gd, Sm and Er.

  The piezoelectric ceramic composition has 0.91 ≦ α ≦ 1.00, 0 <β ≦ 0.08, 0.125 ≦ x ≦ 0.300, 0.020 ≦ y ≦ 0.050, and 0.040 ≦. It is preferable to satisfy z ≦ 0.070. Thereby, the length of the a-axis in the crystal lattice of the piezoelectric ceramic composition can be reliably set to 3.91 to 4.02 angstroms.

If α is less than 0.91, the resistivity of the piezoelectric ceramic composition tends to decrease, and thus there is a tendency that the polarization treatment for imparting piezoelectricity to the piezoelectric ceramic composition is difficult at the time of manufacturing the piezoelectric element 2. . When α exceeds 1.00, the Q _{max of} the oscillator 1 tends to decrease. By setting α within the above range, these tendencies can be suppressed. From the same viewpoint, it is preferable that 0.93 ≦ α ≦ 0.98. Note that Q _max is tan θ _max when the maximum value of the phase angle is θ _max (unit: deg). In other words, the resonance frequency fr and anti-resonance when X is reactance and R is resistance This is the maximum value of Q (= | X | / R) between the frequency fa. When the oscillator 1 is used in an oscillation circuit, it is required that the Q _{max of the} oscillator 1 is large in order to guarantee the oscillation characteristics.

When the piezoelectric ceramic composition contains Ln within the range of 0 <β ≦ 0.08, Q _max is improved. If β is 0, the sinterability of the piezoelectric element 2 tends to deteriorate, and piezoelectric characteristics may not be obtained appropriately. On the other hand, if β exceeds 0.08, the Curie temperature decreases, and the piezoelectric element 2 tends to be easily depolarized when heated. By setting β within the above range, these tendencies can be suppressed. From the same viewpoint, it is preferable that 0.02 ≦ β ≦ 0.06.

It is particularly important that the piezoelectric ceramic composition satisfies 0.125 ≦ x ≦ 0.300 in order to make the length of the a-axis more reliably 3.91 to 4.02 angstroms. If x is less than 0.125, the temperature characteristic of the oscillation frequency F ₀ tends to decrease. If x exceeds 0.300, the Curie temperature decreases, and depolarization occurs when the piezoelectric element 2 is heated. It tends to be easier. By setting x within the above range, these tendencies can be suppressed. From the same viewpoint, it is preferable that 0.13 ≦ x ≦ 0.16. If x ≧ 0.125, the ratio of ZrO _{2 to} the weight of the portion derived from the oxides of Pb, Ln and Ti in the composite oxide of chemical formula (1) exceeds 5% by weight, A relatively large amount of ZrO ₂ is contained in the composite oxide.

If y is less than 0.020, Q _max tends to be small. On the other hand, if y exceeds 0.050, the resistivity of the piezoelectric ceramic composition is likely to decrease, and therefore, it is difficult to perform a polarization treatment for imparting piezoelectricity to the piezoelectric ceramic composition during the manufacture of the piezoelectric element 2. Tend. By setting y within the above range, these tendencies can be suppressed. From the same viewpoint, it is preferable that 0.020 ≦ y ≦ 0.037.

  If z is less than 0.040, the sinterability of the piezoelectric element 2 tends to deteriorate. When z exceeds 0.070, the specific resistance of the piezoelectric element 2 becomes too high, and the characteristic deterioration due to the thermal shock test tends to increase. By setting z within the above range, these tendencies can be suppressed. From the same viewpoint, it is preferable that 0.053 ≦ z ≦ 0.070.

  The piezoelectric ceramic composition has a composition represented by the above chemical formula (1), but contains a compound of a metal element other than Pb, Ln, Ti, Zr, Mn and Nb as an impurity or a trace additive. May be. Such compounds include, for example, oxides of Na, K, Al, Si, P, Ca, Fe, Zn, Hf, W, Cu or Ta. In addition, when the said piezoelectric ceramic composition contains these oxides etc., the total value of the content rate of each oxide in a piezoelectric ceramic composition is 0. 0 of the whole piezoelectric ceramic composition in conversion of the oxide of each element. It is preferably 01% by weight or less (in the case of Hf oxide, 0.3% by weight or less). In other words, 99.9% by weight or more of the piezoelectric ceramic composition is preferably a composite oxide composed of an oxide of Pb, Ln, Ti, Zr, Mn, or Nb.

In the piezoelectric ceramic composition, part of Pb and Ln located at the A site of the perovskite crystal structure ABO ₃ may be substituted with an alkaline earth metal such as Ca, Sr, or Ba.

  The above-described method for manufacturing the oscillator 1 according to the present embodiment mainly includes a step of granulating the raw material powder of the piezoelectric element 2, a step of pressing the raw material powder to form a formed body, and firing the formed body. A step of forming the sintered body, a step of polarizing the sintered body to form the piezoelectric element 2, and a step of forming the vibrating electrode 3 on the piezoelectric element 2. Hereinafter, a method for manufacturing the oscillator 1 will be specifically described.

First, a starting material for forming a piezoelectric ceramic composition is prepared. As the starting material, oxides of each element constituting the piezoelectric ceramic composition having the perovskite crystal structure represented by the above chemical formula (1) and / or compounds that become these oxides after firing (carbonates, hydroxides) Oxalate, nitrate, etc.). As a specific starting material, PbO, a compound of a lanthanoid element (for example, La ₂ O ₃ , La (OH) _3, etc.), TiO ₂ , ZrO ₂ , MnO _2, MnCO ₃ , Nb ₂ O ₅ or the like can be used. That's fine. Each of these starting materials is blended in a weight ratio such that a piezoelectric ceramic composition having the composition represented by the chemical formula (1) is formed after firing.

  Next, the blended starting materials are wet mixed by a ball mill or the like. The wet-mixed starting material is temporarily molded to form a temporary molded body, and the temporary molded body is temporarily fired. By this temporary baking, the temporary baking body containing the piezoelectric ceramic composition of this embodiment mentioned above is obtained. The calcination temperature is preferably 800 to 1050 ° C., and the calcination time is preferably about 1 to 3 hours. If the pre-baking temperature is too low, the chemical reaction tends not to proceed sufficiently in the temporary molded body. If the temporary baking temperature is too high, the temporary molded body starts to sinter, and the subsequent pulverization tends to be difficult. is there. The pre-baking may be performed in the air, or may be performed in an atmosphere having a higher oxygen partial pressure or in a pure oxygen atmosphere than in the air. Further, the wet-mixed starting material may be temporarily fired as it is without being temporarily formed.

  The obtained calcined product is slurried and finely pulverized (wet pulverized) with a ball mill or the like, and then dried to obtain a fine powder. If necessary, a binder is added to the obtained fine powder to granulate the raw material powder. In addition, it is preferable to use alcohol, such as water and ethanol, or a mixed solvent of water and ethanol, as a solvent for slurrying the calcined body. Examples of the binder added to the fine powder include commonly used organic binders such as polyvinyl alcohol, polyvinyl alcohol added with a dispersant, and ethyl cellulose.

  Next, a compact is formed by press molding the raw material powder. What is necessary is just to set the load at the time of press molding to 100-400 Mpa, for example.

  The resulting molded body is subjected to binder removal treatment. The binder removal treatment is preferably performed at a temperature of 300 to 700 ° C. for about 0.5 to 5 hours. The binder removal treatment may be performed in the air, or may be performed in an atmosphere having a higher oxygen partial pressure than the air or a pure oxygen atmosphere.

  After the binder removal treatment, the compact is fired to obtain a sintered body made of the piezoelectric ceramic composition. The firing temperature may be about 1150 to 1250 ° C., and the firing time may be about 1 to 8 hours. In addition, the binder removal treatment and firing of the molded body may be performed continuously or separately.

  Next, the sintered body is cut into a thin plate, and this is lapped and surface-treated. When the sintered body is cut, a cutting machine such as a cutter, a slicer, or a dicing saw can be used. After the surface processing, provisional electrodes for polarization treatment are formed on both surfaces of the thin plate-like sintered body. As the conductive material constituting the temporary electrode, Cu is preferable because it can be easily removed by etching with a ferric chloride solution. For forming the temporary electrode, it is preferable to use a vacuum deposition method or sputtering.

  A polarization electric field is applied to a thin plate-like sintered body on which a temporary electrode for polarization treatment is formed, and polarization treatment is performed. The conditions for the polarization treatment may be appropriately determined according to the composition of the sintered body (piezoelectric ceramic composition). Usually, the temperature of the sintered body subjected to the polarization treatment is 150 to 300 ° C., and the time for applying the polarization electric field. The polarization electric field may be 0.9 times or more the coercive electric field of the sintered body for 1 to 30 minutes.

  After the polarization treatment, the temporary electrode is removed from the sintered body by etching or the like. Then, the sintered body is cut into a desired element shape to form the piezoelectric element 2. By forming the vibrating electrode 3 on the piezoelectric element 2, the resonator 1 of the present embodiment is completed. For the formation of the vibrating electrode 3, it is preferable to use a vacuum deposition method or sputtering.

  The preferred embodiments of the piezoelectric ceramic composition and the oscillator according to the present invention have been described above, but the present invention is not necessarily limited to the above-described embodiments.

  For example, the piezoelectric ceramic composition of the present invention includes a filter, an actuator, an ultrasonic cleaner, an ultrasonic motor, a vibrator for an atomizer, a fish detector, a shock sensor, an ultrasonic diagnostic device, and a waste toner sensor in addition to an oscillator. It may be used for a gyro sensor, a buzzer, a transformer or a lighter.

  Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to these examples.

As a starting material of the piezoelectric ceramic composition, lead oxide (PbO), lanthanum hydroxide (La (OH) ₃ ), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), manganese carbonate (MnCO ₃ ), niobium oxide ( Nb ₂ O ₅ ), cerium oxide (CeO ₂ ), praseodymium oxide (Pr ₆ O ₁₁ ), strontium carbonate (SrCO ₃ ), and manganese carbonate (MnCO ₃ ) powder raw materials were prepared.

  Next, each powder raw material was weighed and blended so that the piezoelectric ceramic composition constituting the porcelain sample (sintered body) after the main firing had the composition of “Sample 1” in Table 1. Next, the blended powder raw material mixture and pure water were mixed with a Zr ball by a ball mill for 10 hours to obtain a slurry. This slurry was sufficiently dried and then press-molded, and this was temporarily fired at 900 ° C. to obtain a temporarily fired body. Next, the calcined product was finely pulverized with a ball mill, and then dried and granulated by adding an appropriate amount of PVA (polyvinyl alcohol) as a binder. About 3 g of the obtained granulated powder was placed in a 20 mm long × 20 mm wide mold and molded using a uniaxial press molding machine with a load of 245 MPa. The molded sample was heat-treated to remove the binder, followed by main firing at 1150 to 1250 ° C. for 2 hours to obtain a porcelain sample (sample 1) which is a sintered body composed of the piezoelectric ceramic composition. A plurality of porcelain samples as “Sample 1” were prepared by the same operation.

One of the obtained porcelain samples was flattened to a thickness of 0.4 mm with a double-sided lapping machine, and then cut into a size of 6 mm length × 6 mm width with a dicing saw. A pair of Ag electrodes having a size of 5 mm × 5 mm was formed by vacuum-depositing an Ag paste on both ends of the cut ceramic sample. After installing the porcelain sample on which the Ag electrode is formed in the electric furnace, the LCR meter is used to measure the temperature at which the capacitance of the porcelain sample reaches the maximum value in the temperature raising process and the temperature lowering process. The Curie temperature _Tc was determined from the average value. The results are shown in Table 1. In addition, since it is necessary that the piezoelectric element does not depolarize even if the oscillator is exposed to a high temperature in a process such as solder reflow, the Curie temperature Tc is preferably as high as possible and particularly preferably 300 ° C. or more.

An X-ray diffraction pattern of a porcelain sample (sample 1) different from that for measuring the Curie temperature _Tc was measured. From the X-ray diffraction pattern, it was confirmed that Sample 1 had a tetragonal perovskite crystal structure at room temperature. Further, from the calculation from the X-ray diffraction pattern, it was confirmed that the length of the a-axis (hereinafter referred to as a-axis length) of the crystal lattice of the perovskite crystal structure was 3.914 Å.

A porcelain sample (sample 1) different from that for measuring the Curie temperature _Tc was flattened to a thickness of 0.4 mm with a double-sided lapping machine, and then cut into a size of 16 mm length × 16 mm width with a dicing saw. A pair of temporary electrodes for polarization treatment having a size of 15 mm × 15 mm was formed by applying an Ag paste to both ends of the cut ceramic sample. The porcelain sample on which the temporary electrode was formed was subjected to polarization treatment by applying a polarization electric field twice the coercive electric field for 15 minutes in a silicon oil bath at a temperature of 120 ° C. After the polarization treatment, the porcelain sample from which the temporary electrodes had been removed was again polished to a thickness of about 0.25 mm with a lapping machine, and processed into a 7 mm × 4.5 mm piezoelectric element 2 with a dicing saw. Next, the vibrating electrodes 3 were formed on both surfaces of the piezoelectric element 2 using a vacuum deposition apparatus, and the resonator 1 having the same configuration as that shown in FIGS. The vibrating electrode 3 was composed of an Ag layer having a thickness of 1.5 μm.

Next, as shown in FIG. 3, parallel capacitors C _L1 and C _L2 having a predetermined capacitance were connected to the oscillator 1 to form a Colpitts oscillation circuit 20 together with the IC. In the Colpitts oscillation circuit 20, Rf is a feedback resistor and Rd is a limiting resistor. The Colpitts oscillation circuit 20 was connected to a predetermined DC power source (not shown). The Colpitts oscillation circuit 20 is placed in a constant temperature bath at 25 ° C., and the oscillation frequency F ₀ (25 ° C.) when the temperature in the bath is stabilized at 25 ° C. (when the temperature T of the oscillator 1 is stabilized at 25 ° C.). Was measured. In the measurement of F ₀ (25 ° C.), a frequency counter (53181A manufactured by Agilent Technologies) was used. Furthermore, in the same manner as F ₀ (25 ° C.), F ₀ (−40 ° C.), F ₀ (−20 ° C.), F ₀ (−10 ° C.), F ₀ (0 ° C.), F ₀ (50 ° C.) ), F ₀ (70 ° C.), and F ₀ (85 ° C.), respectively.

_{Then, RF 0 (T) = {} F 0 (T) -F 0 (T 0)} / F 0 (T 0) × 100 ··· F 0 (T 0) to _{F 0} in Equation (1) ( RF ₀ (−40 ° C.) (unit:%) was calculated by substituting the measured value of 25 ° C.) and substituting the measured value of F ₀ (−40 ° C.) for F ₀ (T). Further, in the same manner as RF ₀ (−40 ° C.), RF ₀ (−20 ° C.), RF ₀ (−10 ° C.), RF ₀ (0 ° C.), RF ₀ (25 ° C.), RF ₀ (50 ° C.) ), RF ₀ (70 ° C.), and RF ₀ (85 ° C.), respectively. These values are shown in Table 2. In addition, Table 1 shows the larger one of RF ₀ (−40 ° C.) and RF ₀ (85 ° C.) (hereinafter referred to as F ₀ change rate). It means that the smaller the absolute value of the F ₀ change rate, the more stable the oscillation frequency F ₀ with respect to the temperature change, and the better the temperature characteristic of F ₀ .

As shown in FIG. 4, with respect to the temperature T of the oscillator 1, RF ₀ (−40 ° C.), RF ₀ (−20 ° C.), RF ₀ (−10 ° C.), RF ₀ (0 ° C.), RF ₀ (25 ° C.), RF ₀ (50 ° C.), RF ₀ (70 ° C.), RF ₀ (85 ° C.) are plotted, and quadratic function RF ₀ (T) = aT ² + bT + c (a, b, c is Each is a real number)... The curvature 2a of the rate of change RF ₀ (T) of the oscillation frequency F ₀ in the oscillator 1 made of the sample 1 was obtained by fitting the mathematical formula (2). The results are shown in Table 1. Higher curvature 2a is small, and the change rate RF ₀ of the oscillation frequency F ₀ with respect to the temperature change of the oscillator 1 is stable, which means that the temperature characteristic of the oscillation frequency F ₀ is good. The curve of Sample 1 shown in FIG. 4 is an approximate curve that is not a quadratic curve for convenience of illustration. The same applies to the curves of samples 6, 7, and 15 described later.

Next, except that each powder raw material was blended so that the piezoelectric ceramic composition constituting the porcelain sample (sintered body) after the main firing had the respective compositions of Samples 2 to 20 shown in Table 1. Porcelain samples as Samples 2 to 20 were produced in the same manner as Sample 1. Further, when X-ray diffraction patterns were measured for Samples 2 to 20, it was confirmed that all of Samples 2 to 20 had a tetragonal perovskite crystal structure at room temperature. Further, the a-axis lengths of Samples 2 to 20 were determined from the X-ray diffraction patterns of Samples 2 to 20, respectively. The results are shown in Table 1. Further, the Curie temperature T _c , the F ₀ change rate, and the curvature 2a of each of the samples 2 to 20 were determined by the same method as the sample 1. The results are shown in Table 1. In FIG. 5, the curvature 2a of the samples 1 to 19 is plotted against the a-axis length of the samples 1 to 19. For sample 20, RF ₀ (T) was not a quadratic function of T but a cubic function, so the curvature 2a could not be obtained. Therefore, the sample 20 is not plotted in FIG.

As shown in Table 1, in samples 1 to 13 and 15 to 19 having an a-axis length of 3.91 to 4.02 angstroms, the absolute value of the F ₀ change rate is small and the high Curie temperature T _c is high. Expression was confirmed. On the other hand, Samples 14 and 20 whose a-axis length was outside the range of 3.91 to 4.02 angstroms had a larger absolute value of F ₀ change rate than Samples 1 to 13 and 15 to 19.

  As shown in FIG. 5, since the curvature 2a and the a-axis length have a correlation, the curvature 2a can be changed by controlling the a-axis length. For example, if the a-axis length is in the range of 3.91 to 4.02 angstroms, the curvature 2a can be 20 or less.

From the above experimental results, according to the present invention, it is possible to obtain a favorable temperature characteristic of the oscillation frequency F ₀ even when used in an oscillator using the third harmonic mode of thickness longitudinal vibration. It has been confirmed that a piezoelectric magnetic composition is provided.

1 is a perspective view showing an oscillator according to an embodiment of the present invention. It is arrow sectional drawing along the II-II line | wire of FIG. It is a Colpitts oscillation circuit diagram provided with an oscillator. 5 is a graph in which a change rate RF ₀ is plotted against a temperature T of an oscillator. It is the graph which plotted the curvature 2a with respect to a-axis length.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Oscillator, 2 ... Piezoelectric element, 3 ... Vibrating electrode.

Claims (3)

It has a tetragonal perovskite crystal structure,
A piezoelectric ceramic composition having an a-axis length of 3.91 to 4.02 angstroms in the crystal lattice of the perovskite crystal structure. _{(Pb α Ln β) (Ti} 1- (x + y + z) Zr x Mn y Nb z) O 3
[Wherein, Ln represents at least one selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. ]
Having a composition represented by
0.91 ≦ α ≦ 1.00,
0 <β ≦ 0.08,
0.125 ≦ x ≦ 0.300,
0.020 ≦ y ≦ 0.050, and 0.040 ≦ z ≦ 0.070
The piezoelectric ceramic composition according to claim 1, wherein:   An oscillator comprising a piezoelectric element comprising the piezoelectric ceramic composition according to claim 1.

Images