JP2001158663A - Piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition having high temperature stability of the oscillating frequency, as the P/V value of the fundamental vibration is enlarged in the thickness and slip vibrations. SOLUTION: This piezoelectric ceramic composition comprises 100 pts.wt. of a Bi-layer structure compound represented by the general formula: (Na0.5 Bi0.5)1-xMxBi4Ti4O15 (where x is 0.5<x<1) and 0.05-1 pt.wt. of Mn calculated as the oxide.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition, for example, an oscillator, an ultrasonic oscillator, an ultrasonic motor or an acceleration sensor, a knocking sensor, and an A.
The present invention relates to a piezoelectric ceramic composition suitable for a piezoelectric sensor such as an E sensor and the like, and particularly suitable for use as an energy trapping type high frequency oscillator utilizing fundamental vibration of thickness shear vibration.

[0002]

2. Description of the Related Art Conventionally, products using a piezoelectric ceramic composition include, for example, filters, resonators, oscillators, ultrasonic oscillators, ultrasonic motors, piezoelectric sensors, and the like.

Here, the oscillator is used for oscillation of a reference signal of a microcomputer, for example, incorporated in an oscillation circuit such as a Colwitz oscillation circuit. As shown in FIG. 1, the Colpitts oscillation circuit includes capacitors 11 and 12, a resistor 13, an inverter 14, and an oscillator 15. In order to generate an oscillation signal in a Colpitts oscillation circuit, the following oscillation conditions must be satisfied.

In an amplifier circuit comprising an inverter 14 and a resistor 13, the amplification factor is α and the phase shift amount is θ _{1. In} a feedback circuit comprising an oscillator 15 and capacitors 11 and 12, the feedback ratio is β and When the amount is θ ₂ , the loop gain is α × β ≧ 1, and the phase shift amount is θ ₁ + θ ₂ = 360 ×
n (where n = 1, 2,...).

Generally, an amplifier circuit including the resistor 13 and the inverter 14 is built in the microcomputer, and in order to obtain stable oscillation without causing erroneous oscillation or non-oscillation, the loop gain must be increased. In order to increase the loop gain, P / V value of the oscillator to determine the gain of the feedback factor beta, that is, necessary to increase the difference in resonance impedance R ₀ and the anti-resonance impedance R _a. The P / V value is defined as _a value of 20 Log (R _a / R ₀ ).

In order to satisfy the condition of the phase amount, Q
Piezoelectric materials with a high _m are desirable. For example, conventional PZT
Quality factor (Q _m
Value) of SrBi ₄ T ₄ O ₁₅
Applied Physics (1974), pages 1572-1577. According to it, whereas the Q _m value of PbTiO ₃ is 1100, SrBi ₄ T ₄ O ₁₅ is high as 7200 is obtained. Thus, the bismuth layered compound SrBi ₄ T ₄ O ₁₅ is characterized by a high Q _m value,
In particular, it could be applied to piezoelectric materials for oscillators.

[0007]

However, the bismuth layered compound (SrBi ₄ T ₄ O ₁₅ ) disclosed in the above-mentioned document is required.
When used as a resonator, a piezoelectric ceramic composition mainly composed of: has a problem that the temperature change rate of the resonance frequency is as large as ± 5000 ppm or more and cannot be used for a portable device used in an environment where the temperature change is large. .

Therefore, the present invention increases the P / V value of the fundamental vibration of the thickness-shear vibration and increases the P / V value from -40.degree.
An object of the present invention is to provide a piezoelectric ceramic composition having excellent oscillation frequency temperature stability in a temperature range of 0 ° C.

[0009]

Means for Solving the Problems The piezoelectric ceramic composition of the present invention
Represents that M is at least one selected from divalent metal elements.
When a seed is used, the general formula (Na_0.5Bi_0.5)_1-xM_xBi
_FourTi_FourO_Fifteen (Where x is represented by 0.5 <x <1)
Mn is oxidized with respect to 100 parts by weight of Bi layer structure compound
Characterized by containing 0.05 to 1 part by weight in terms of material
That is, a representative of the Bi layered compound which is a lead-free piezoelectric material
Material Sr_FourBi_FourTi_FourO_FifteenOf Sr (Na_0.5B
i_0.5) And a divalent metal element (Na _0.5Bi
_0.5)_1-xM_xBi_FourTi_FourO_FifteenAnd containing Mn
By doing so, the P / V value of the fundamental wave vibration of the thickness slip vibration (hereinafter
(Sometimes simply referred to as the P / V value).
And at the same time, the oscillation frequency at -40 ° C to 80 ° C
Temperature change rate can be kept low,
It can be suitably used for an oscillator.

Therefore, when used as an oscillator, the oscillation margin is increased and stable oscillation can always be obtained, and the oscillation frequency is stable over a wide temperature range, so that highly accurate oscillation can be obtained. That is, by using the fundamental wave vibration in the thickness shear vibration, a high frequency, especially 2 to 20 M
The oscillator which can be adapted to Hz can be obtained.

Preferably, the divalent metal element M is at least one selected from Ca, Sr and Ba. Thereby, the P / V value can be further increased.

Further, when the divalent metal M is composed of Sr and another divalent metal element N, and M is represented by the general formula, Sr _1-y N _y , 0.05 ≦ y ≦ 0.5 It is preferred that
That is, since Sr has a function of significantly increasing the P / V value, by combining it with another divalent metal element N,
The temperature stability of the oscillation frequency can be further improved while keeping the P / V value high.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The piezoelectric ceramic composition of the present invention has a general formula (Na _0.5 Bi _0.5 ) _1-x M _x Bi ₄ Ti ₄ O ₁₅ (where x
Has a Bi layered compound represented by 0.5 <x <1) as a main component, and contains 0.05 to 1 part by weight of Mn in terms of oxide based on 100 parts by weight of the main component. .

Here, as the divalent metal element, Ca,
There are Sr, Ba, Ra and the like.
Some (Na_0.5Bi_0.5), But the
The substitution amount 1-x is 0 <1-x <0.5, particularly 0.1 ≦ 1.
-X≤0.4, and set to 0.2≤1-x≤0.3
By doing so, the P / V value is increased, and the temperature of the oscillation frequency is increased.
The degree of rate change can be reduced. However, divalent gold
(Na _0.5Bi_0.51)
When x is 0.5 or more, the P / V value decreases, and -4
Large temperature change rate of oscillation frequency from 0 ° C to 80 ° C
turn into.

[0015] Further, Mn is based on 100 parts by weight of the main component.
The P / V value can be remarkably improved by setting the content to 0.05 to 1.0 part by weight, particularly 0.1 to 0.4 part by weight, in terms of oxide. When the content of Mn is less than 0.05 parts by weight in terms of oxide, P / V is greatly reduced, and l. If the amount is more than 0 parts by weight, the volume resistivity of the sintered body decreases and polarization becomes difficult.

Therefore, (N
When the substitution amount 1-x of a _0.5 Bi _0.5 ) and the Mn content are set as described above, the P / V value can be increased to 50 dB or more due to the synergistic effect of the substitution effect and the Mn effect. At the same time, the temperature change rate of the oscillation frequency at −40 ° C. to 80 ° C. can be set to −5000 to 5000 ppm.

Further, the piezoelectric ceramic composition of the present invention comprises:
By using at least one selected from Ca, Sr, and Ba, the P / V value can be further improved.

Particularly, when M is a combination of Sr and another divalent metal element N, a higher P / V value and a temperature change rate closer to 0 can be obtained. That is, M is represented by the general formula Sr _1-y N _y , and the Bi layered compound as the main component is represented by the general formula (Na _0.5 Bi _0.5 ) _1-x (Sr
_1-y N _y ) _x Bi ₄ Ti ₄ O ₁₅ (where x is 0.5 <x <
When represented by 1), by setting 0.05 ≦ y ≦ 0.5, the P / V value is 60 dB or more, and the temperature change rate of the oscillation frequency at −40 ° C. to 80 ° C. is −3800 to 3800.
ppm. In particular, 0.1 ≦ y ≦ 0.4
Is desirable.

In the piezoelectric ceramic composition of the present invention, a bismuth layered compound represented by (Na _0.5 Bi _0.5 ) _1-x M _x Bi ₄ Ti ₄ O ₁₅ is used as a main crystal phase. Mn may form a solid solution in the main crystal phase and partially precipitate as crystals of the Mn compound at the grain boundaries of the main crystal phase. In addition, in the piezoelectric ceramic composition of the present invention, a pyrochlore crystal phase and a perovskite crystal phase may be present as crystal phases other than the bismuth layered compound, but there is no problem in characteristics as long as the amount is small.

The piezoelectric ceramic composition of the present invention is prepared, for example, by using Na ₂ CO ₃ , Bi ₂ O ₃ , SrCO ₃ , CaC
Powder such as O ₃ , BaCO ₃ , MnO ₂ , TiO ₂ is used.

After these raw materials are weighed and mixed so as to have the composition of the porcelain composition of the present invention, the mixture is mixed with 85%.
The mixture is calcined at 0 to 1050 ° C, a predetermined organic binder is added, dry-mixed, and granulated. The powder thus obtained is formed into a predetermined shape by known press molding or the like, and calcined in an oxidizing atmosphere such as air at a temperature range of 1000 to 1300 ° C. for 2 to 5 hours. A composition is obtained.

The same effect can be obtained by mixing the metal oxide used as a raw material not only at the time of blending but also with the calcined powder during the above manufacturing process. The raw material powder to be used is not limited to carbonates and oxides, and may be any compound such as acetate or organic metal as long as it becomes an oxide by a heat treatment process such as firing.

Further, in the piezoelectric ceramic according to the present invention, the Al, Si, Z
An unavoidable impurity such as r or Ta may be mixed in, but there is no problem as long as the characteristics are not affected.

The piezoelectric ceramic composition of the present invention is most suitable as a piezoelectric ceramic composition for an oscillator of a Colpitts type oscillation circuit as shown in FIG. 1, but other oscillators, ultrasonic oscillators,
The piezoelectric ceramic composition is most suitable for an ultrasonic motor and a piezoelectric sensor such as an acceleration sensor, a knocking sensor, and an AE sensor, and is particularly suitable as a high-frequency oscillator utilizing a fundamental wave vibration of a thickness-shear vibration.

[0025]

EXAMPLE The piezoelectric ceramic composition of the present invention was prepared by first using Na ₂ C having an average particle size of 1.5 μm and a purity of 99.9% as a starting material.
O ₃ powder, Bi ₂ O ₃ powder, and TiO ₂ powder were weighed, and MnO ₂ powder having an average particle diameter of 1.2 μm and a purity of 99.9%, and optionally CaCO ₃ powder, SrCO ₃ powder and BaC
It was prepared using O ₃ powder so as to have the composition shown in Table 1 in the above composition formula. Next, the zirconia balls having a purity of 99.9% and isopropyl alcohol (IPA) were put into a 500 ml polypot, and mixed with a rotary mill for 16 hours. The mixed slurry is dried in the atmosphere, and # 4
After passing through 0 mesh, it was calcined at 950 ° C. for 3 hours in the atmosphere to obtain an evaluation powder.

An appropriate amount of an organic binder is added to the powder, and the mixture is granulated.
m, width 38 mm, thickness l. It was formed into a 0 mm plate shape and fired in air at a temperature of 1140 ° C. for 3 hours to obtain a piezoelectric ceramic.

The resulting porcelain was 6 mm long, 30 mm wide,
Processed to a thickness of 0.60 mm and polarized in the length direction,
A polarization electrode was provided on the end face to perform polarization processing. Next, after removing the electrode for polarization to a thickness of 0.23 mm,
Ag and Cr were simultaneously vapor-deposited on both surfaces having a length of 6 mm and a width of 30 mm, and annealed at 250 ° C. for 12 hours.

Next, the vapor deposition layer made of Ag and Cr formed at unnecessary portions of the electrodes is removed by etching, cut, and the fundamental wave vibration of thickness slip vibration corresponding to 8 MHz oscillation as shown in FIG. An oscillator using was manufactured. This sample had a length of 4.5 mm (L), a width of 1.1 mm (W), and a thickness of 0.23 mm (H), and had electrodes on the upper and lower surfaces. The arrow P in FIG. 2 indicates the direction of polarization.

As for the characteristics of the oscillator, a re-impedance waveform was measured by an impedance analyzer, and P / V at the fundamental wave vibration of the thickness shear vibration was calculated by the following equation. P / V value = 20 Log (R _a / R ₀ ) where _Ra : anti-resonance impedance, R ₀ : resonance impedance Further, the temperature change rate of the oscillation frequency at −40 ° C. to 80 ° C. was measured. The temperature change rate of this resonance frequency is 25
Based on ° C, it was calculated by the following equation. Fosc change rate (ppm) = ｛(Fosc (drift) −Fos
c (25)) / Fosc (25)｝ × 100, where F
The osc change rate is a temperature change rate of the resonance frequency, and
Fosc (dshift) is the resonance frequency at -40 ° C or + 80 ° C, and Fosc (25) is the oscillation frequency at 25 ° C. And -40 to 25 ° C or 25 to
The larger value of 80 ° C. was defined as the temperature change rate. Table 1 shows the results.

[0030]

[Table 1]

Sample No. of the present invention 1,2,4-7,10
To 15 and 17 to 22 are the P of the fundamental wave vibration of the thickness shear vibration.
/ V value was 50 dB or more, and the absolute value of the temperature change rate of the resonance frequency at −40 ° C. to 80 ° C. was 4100 ppm or less. In particular, when the content of Mn is 0.1 to
Sample No. 0.4 parts by weight. In Nos. 11 to 13, the P / V value of the fundamental wave vibration of the thickness shear vibration was 55 dB or more.

The sample No. of the present invention in which the divalent metal element M was Sr and another divalent metal N was used. 17-22 are P /
V value is 60 or more, temperature change rate of resonance frequency is 3800p
pm or less.

On the other hand, the sample No. 2 in which the divalent metal element M is Ba and the value of x is out of the range of the present invention. In Nos. 3 and 8, the P / V value was 45 and 48 dB, and the temperature change rate of the resonance frequency was 3500 and 5100 ppm, respectively.

Sample No. 2 in which the divalent metal element M is Ba and the Mn content is out of the range of the present invention. Sample No. 9 had a P / V value of 22 dB, and No. 15 could not be polarized because the content of Mn was too large.

[0035]

The piezoelectric ceramic composition of the present invention can increase the P / V value of the fundamental wave vibration in the thickness shear vibration,
At the same time, the rate of temperature change of the oscillation frequency in the temperature range of -40 ° C to 80 ° C can be reduced, so that a piezoelectric ceramic composition excellent in temperature stability of the oscillation frequency can be obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a Colpitts type oscillation circuit.

FIG. 2 is a perspective view of an oscillator for 8 MHz.

[Explanation of symbols]

 11, 12 ... capacitor 13 ... resistor 14 ... inverter 15 ... oscillator

Claims (3)

[Claims] When M is at least one selected from divalent metal elements, a general formula: (Na _0.5 Bi _0.5 ) _1-x M _x Bi ₄ Ti ₄ O ₁₅ (where x
Is characterized by containing 0.05 to 1 part by weight of Mn in terms of oxide based on 100 parts by weight of the main component comprising a Bi layer structure compound represented by 0.5 <x <1). Piezoelectric ceramic composition. 2. The method according to claim 1, wherein the divalent metal element M is Ca, Sr or B
2. The piezoelectric ceramic composition according to claim 1, wherein the composition is at least one selected from a. Wherein the divalent metal element M consists of Sr and other divalent metal elements N, when M is the formula, expressed in _{Sr 1-y N y, 0.05} ≦ y ≦ 0 3. The piezoelectric ceramic composition according to claim 1, wherein the composition is 0.5.