JP2001019541A - Piezoelectric ceramic composition - Google Patents

Abstract

(57) [Problem] To provide a piezoelectric ceramic composition which is lead-free and has a high P / V value even when fired under normal pressure. A least Ba as the metal element, Bi and containing Ti, xBaO the composition formula by molar ratio of a metal element oxide _{· yBi 2 O 3 · zTiO 2} (x + y + z =
When expressed as 1), x, y and z are A (0.157)
5, 0.2740, 0.5685), B (0.115
4, 0.3077, 0.5769), C (0.156
8, 0.1716, 0.6716), D (0.184
2, 0.1579, 0.6579).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric ceramic composition, and more particularly to a piezoelectric ceramic composition suitable for a resonator.

[0002]

2. Description of the Related Art Conventionally, products using a piezoelectric ceramic composition include, for example, a filter, a resonator, an oscillator, an ultrasonic oscillator, an ultrasonic motor, and a piezoelectric sensor.

The oscillator is used as a reference signal oscillator of a microcomputer, for example, incorporated in a Colpitts type oscillation circuit. This Colpitts-type oscillation circuit includes a capacitor, a resistor, an inverter, and an oscillator.

In a Colpitts type oscillation circuit,
In order to generate an oscillation signal, it is necessary to satisfy the following oscillation conditions in relation to the loop gain and the phase shift amount.

The amplification factor of an amplifier consisting of an inverter and a resistor is α, the phase shift amount is θ ₁ , the feedback ratio of a feedback circuit consisting of an oscillator and a capacitor is β, and the phase shift amount is θ.
_{When 2} , the loop gain is α × β ≧ 1, and the phase shift amount is θ ₁ + θ ₂ = 360 degrees × n (where n = 1, 2,
3 ...).

In order to obtain stable oscillation in a Colpitts type oscillation circuit, the loop gain must be increased. Therefore, oscillator P / V value that determines the gain of the feedback factor beta, i.e. it is necessary to increase the difference in resonance impedance R ₀ and anti-resonance impedance R _a. Note that the P / V value is defined as _a value of 20 Log (R _a / R ₀ ).

Conventionally, as such a piezoelectric ceramic composition,
Those containing PbTiO ₃ or Pb (Ti, Zr) O ₃ as a main component, or Pb (Mn _1/3 Nb _2/3 ) O ₃ or Pb (Ni _{1 / 3} N
b _2/3 ) O ₃ and the like are known.
In particular, a piezoelectric ceramic composition containing PbTiO ₃ as a main component has a characteristic that its relative dielectric constant is as small as 300 to 700 and that it can be used in a high frequency region of 10 MHz or more.

[0008] However, since these materials contain lead harmful to the body, lead may be eluted by acid rain after being discarded, and may contaminate groundwater. Therefore, from the viewpoints of ecological aspects and pollution prevention, there is a demand for a lead-free or low-lead material having excellent piezoelectric properties.

On the other hand, the bismuth layer compound is PbTiO.
₃ and PZT are inferior in piezoelectricity, but PbTiO ₃
And a Curie temperature of 40
Since it is as high as 0 to 600 ° C., it is expected to be used as a lead-free piezoelectric material that can be used in a wide temperature range.

Since the crystal structure of this bismuth layered compound has anisotropy, it is difficult to densify it by normal-pressure sintering, which is a general method for producing ceramics. By adding
A technique has been reported to improve the piezoelectric properties by aligning the crystal axes of plate-like crystals in one direction and improving the piezoelectric properties (JAPANESE JOURN
AL OF APPLIED PHYSICS VOL.19, NO1, JANUARY, 1980 PP31
-39).

[0011]

However, in the hot press method described above, firing must be performed in one direction by pressing, and there is a problem that the mass production is inferior to normal pressure firing.

[0012] The present invention relates to a method for producing lead-free and pulverized even if fired under normal pressure.
It is an object to provide a piezoelectric ceramic composition having a high / V value.

[0013]

The present inventors have proposed Ba, B
By optimizing the ratio of i and Ti, it has been found that the P / V value can be increased even under normal pressure firing, and the present invention has been achieved.

That is, the piezoelectric ceramic composition of the present invention contains at least Ba, Bi and Ti as metal elements, and has a composition formula based on the molar ratio of metal element oxides of xBaO.yBi.
_When expressed as ₂ O ₃ .zTiO ₂ (x + y + z = 1), the x, y and z satisfy a range defined by the following points ABCDCA.

Xyz point A: 0.1575 0.2740 0.5687 point B: 0.1154 0.3077 0.5769 point C: 0.1568 0.1716 0.6716 point D: 0.1842 1579 0.6579 Here, x, y and z are the following points EFGHHI
It is desirable to satisfy the range enclosed by -E.

Xyz point E: 0.1479 0.2817 0.5704 Point F: 0.1269 0.2985 0.5746 Point G: 0.1500 0.2000 0.6500 Point H: 0.1700 2000 0.6300 Point I: 0.1500 0.2600 0.5900 Further, at least one of Mn, Fe, Ni, Co, and Cr is further converted to MnO ₂ , Fe ₂ O ₃ , NiO, C
oO, in a total volume in terms of Cr ₂ O ₃ from 0.05 to 0.8 wt%
It is desirable to contain. The piezoelectric ceramic composition of the present invention,
It is desirable to use it for a resonator. In the present invention, the term “for a resonator” is a concept including a piezoelectric oscillator, a piezoelectric oscillator, and a resonator.

In the piezoelectric ceramic composition of the present invention, P /
It is desirable that the V value be 40 dB or more, particularly, 50 dB or more.

[0018]

[Action] In the piezoelectric ceramic composition of the present invention, xBaO the composition formula by molar ratio _{· yBi 2 O 3 · zTiO 2} (x + y +
When z = 1), x, y and z are represented by points ABC
Ba, Bi, and Ti within the range enclosed by -DA.
Is optimized, the P / V value can be improved to 40 dB or more even in the case of lead-free firing at normal pressure.

Further, x, y and z are represented by the following points EF-
By setting it within the range surrounded by GHIE, P
/ V value can be improved to 50 dB or more.

Further, Mn, Fe, Ni, Co and C
r is at least one of MnO ₂ , Fe ₂ O ₃ , Ni
By containing a predetermined amount in terms of O, CoO, and Cr ₂ O ₃ , the P / V value can be further improved.

By using such a piezoelectric ceramic composition for a resonator, a resonator having excellent characteristics can be obtained.

[0022]

The piezoelectric ceramic composition of the present invention DETAILED DESCRIPTION OF THE INVENTION, xBaO · Ybi the formula by molar ratio ₂ O ₃ · zTiO ₂
When (x + y + z = 1), x, y and z are A
(0.1575, 0.2740, 0.5687), B
(0.1154, 0.3077, 0.5769), C
(0.1568, 0.1716, 0.6716), D
(0.1842, 0.1579, 0.6579).

Here, x, y and z are defined as points ABC-
The reason for setting the range enclosed by DA is that when the Bi content is higher than the AB line, the insulation resistance decreases and the polarization process cannot be performed completely, so that the P / V value decreases. , When the Ba content is lower than that of the BC line, the P / V value is reduced because the content of Bi ₄ Ti ₃ O _{12 having} low piezoelectric properties is increased, and the Ti content is lower than that of the CD line. When large, Ba ₄ Ti _{13 which} does not show piezoelectric characteristics
Since the content of O ₃₀ increases, the P / V value decreases and D-
When the Ba content is higher than that of the A line, the content of Ba ₂ Bi ₄ Ti ₅ O ₁₈ having low piezoelectric properties increases, so that the P content increases.
This is because the / V value decreases.

In the piezoelectric ceramic composition of the present invention, in particular, x,
y and z are E (0.1479, 0.2817, 0.
5704), F (0.1269, 0.2985, 0.5
746), G (0.1500, 0.2000, 0.65
00), H (0.1700, 0.2000, 0.630)
0), I (0.1500, 0.2600, 0.590
It is desirable to control within the range enclosed by 0). By setting it within this range, the P / V value can be made 50 dB or more.

Further, according to the present invention, Mn, Fe, Ni,
At least one of Co and Cr is MnO ₂ , F
_{e 2 O 3, NiO, CoO} , Cr 2 O 3 in terms desirably contains 0.05 to 0.8 wt% in total volume. This is because the effect of improving the electromechanical coupling coefficient is small when the amount is less than 0.05% by weight in the total amount, and the electromechanical coupling coefficient decreases when the amount is more than 0.8% by weight. At least one of Mn, Fe, Ni, Co and Cr is selected from the group consisting of M
nO ₂ , Fe ₂ O ₃ , NiO, CoO, and Cr ₂ O ₃ are desirably contained in the total amount of 0.1 to 0.5% by weight. Among them, it is desirable that Mn be contained in an amount of 0.1 to 0.5% by weight in terms of MnO _{2 based} on the total amount.

The piezoelectric ceramic composition of the present invention uses, for example, BaCO ₃ , Bi ₂ O ₃ , and TiO ₂ as raw material powders.
After weighing the composition so as to have a predetermined molar ratio, and further adding a predetermined amount of MnO ₂ , Fe ₂ O ₃ , NiO, CoO, and Cr ₂ O ₃ powder as required, and calcining the mixed raw material powder. A binder is added and mixed, and the mixture is formed into a predetermined shape by press molding, a doctor blade method, or the like, and the molded body is fired in an oxygen-containing atmosphere such as the air.

In firing the compact, the composition of the porcelain is likely to fluctuate and the piezoelectric characteristics may be degraded because the vapor pressure of bismuth oxide is relatively high. It is desirable to carry out. The firing temperature is in the range of 1,080 to 1,140 ° C.
The firing time may be 2 to 5 hours.

The piezoelectric ceramic composition of the present invention are those which contain BaBi ₄ Ti ₄ O ₁₅ phase as a crystal phase, in particular, be a primary crystal BaBi ₄ Ti ₄ O ₁₅ phases, P
/ V value is desirable.

Further, in the piezoelectric ceramic composition of the present invention, Al, Si, Zr, etc. may be mixed as unavoidable impurities, or when Al or a component of a milling ball for grinding powder is mixed in the manufacturing process. There is.

[0030]

EXAMPLES As raw material powders, BaCO ₃ , Bi ₂ O ₃ , T
Using iO ₂ , the composition formula based on the molar ratio is xBaO · yBi.
_When expressed as ₂ O ₃ .zTiO ₂ (x + y + z = 1),
x, y, and z satisfy Table 1, and MnO ₂ , Fe ₂ O ₃ , NiO, CoO, and Cr ₂ O ₃ are used as raw material powders. Weighed as indicated and wet mixed for 20 hours in a ball mill. After dewatering and drying this mixed powder, it was calcined at 950 ° C. for 3 hours and pulverized.

An appropriate amount of a binder is added to and mixed with the obtained calcined powder, and a diameter of 4 mm and a thickness of 8 are applied under a pressure of 1 t / cm ^2.
mm was molded into a cylinder, the molded body was embedded in the calcined powder, and calcined at 1120 ° C. for 3 hours in the atmosphere to obtain a columnar porcelain.

Silver electrodes were baked on the upper and lower surfaces of these cylinders. The cylinder on which the silver electrode was baked was polarized in a silicon oil set at 200 ° C. by applying an electric field of 10 kV / mm for 60 minutes. Thereafter, the electrical characteristics (resonance / anti-resonance frequency, resonance / anti-resonance impedance) were measured at room temperature with an impedance analyzer, and the electromechanical coupling coefficient (K ₃₃ ) and the P / V value were determined. The results are shown in Table 1.

[0033]

[Table 1]

According to Table 1, any sample whose composition range deviates from the predetermined range (range surrounded by line segment ABCDA) of the ternary composition diagram of FIG. / V value is 40d
B or less.

On the other hand, in each of the samples of the present invention, BaBi ₄ Ti ₄ O ₁₅ was precipitated as a crystal phase, and P
/ V value showed excellent characteristics of 40 dB or more. In particular, in the ternary composition diagram of FIG. 1, the line segment EFGH-
Within the range surrounded by IE, the P / V value is 50 dB.
The above excellent characteristics were exhibited.

[0036]

According to the piezoelectric ceramic composition of the present invention, the composition formula based on the molar ratio is represented by xBaO.yBi ₂ O ₃ .zTiO ₂ (x
+ Y + z = 1), x, y, and z are points A-
Since the ratio of Ba, Bi, and Ti is optimized within the range surrounded by BCDDA, the P / V value can be improved to 40 dB or more even when sintering is lead-free and normal pressure. Thus, an optimal piezoelectric ceramic composition for a resonator can be obtained.

Further, x, y and z are represented by the following points EF-
By setting it within the range surrounded by GHIE, P
/ V value can be improved to 50 dB or more. Further, at least one of Mn, Fe, Ni, Co and Cr is MnO ₂ , Fe ₂ O ₃ , NiO, CoO, Cr
By containing a predetermined amount in terms of ₂ O ₃ , P / V
Value can be improved.

[Brief description of the drawings]

FIG. 1 shows a composition range 3 of the piezoelectric ceramic composition of the present invention.
It is an original composition figure.

Claims (4)

[Claims] 1. A composition containing at least Ba, Bi and Ti as a metal element, and a composition formula based on a molar ratio of a metal element oxide is represented by xBaO.yBi ₂ O ₃ .zTiO ₂ (x + y + z =
1) When x, y and z are represented by the following points ABC
-A piezoelectric ceramic composition characterized by satisfying a range surrounded by DA. xyz point A: 0.1575 0.2740 0.5685 point B: 0.1154 0.3077 0.5769 point C: 0.1568 0.1716 0.6716 point D: 0.1842 0.1579 0. 6579 2. x, y and z are the following points EFGH
2. The piezoelectric ceramic composition according to claim 1, wherein the piezoelectric ceramic composition satisfies the range enclosed by -IE. xyz point E: 0.1479 0.2817 0.5704 Point F: 0.1269 0.2985 0.5746 Point G: 0.1500 0.2000 0.6500 Point H: 0.1700 0.2000 6300 point I: 0.1500 0.2600 0.5900 3. At least one of Mn, Fe, Ni, Co and Cr is selected from MnO ₂ , Fe ₂ O ₃ , NiO, C
oO, in a total volume in terms of Cr ₂ O ₃ from 0.05 to 0.8 wt%
The piezoelectric ceramic composition according to claim 1, wherein the composition is contained. 4. The piezoelectric ceramic composition according to claim 1, which is used for a resonator.