JP3232667B2 - Piezoelectric ceramic - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a ceramic oscillator,
The present invention relates to a piezoelectric element such as a ceramic filter and a ceramic discriminator, and particularly to a piezoelectric ceramic used for a surface mount type piezoelectric component requiring heat resistance.

[0002]

2. Description of the Related Art Conventionally, lead zirconate titanate (Pb) has been used as a piezoelectric ceramic used in ceramic filters and the like.
Piezoelectric ceramics containing (Ti _X Zr _1-X ) O ₃ ) as a main component are widely used, and piezoelectric ceramics to which various trace additives are added in order to improve the piezoelectric properties thereof are used.

In particular, a piezoelectric ceramic for a ceramic filter (piezoelectric filter) having a flat group delay time (GDT) characteristic and a small phase distortion is required to have a small mechanical quality factor Qm value. As a piezoelectric ceramic having a small mechanical quality factor Qm, niobium oxide, antimony oxide, tantalum oxide, or the like is added as an additive to lead zirconate titanate (Pb (Ti _X Zr ₁ -x) O ₃ ). Piezoelectric ceramics and lead zirconate titanate (Pb (Ti _X Zr
Piezoelectric ceramics in which a part of the Pb atom of _1-X ) O ₃ ) is replaced with a rare earth element are known.

[0004] In addition to the above piezoelectric ceramics, Pb (Zr _0.52 T
i _0.48 ) A material in which Mn is diffused in O ₃ has been reported (M. Takahashi and S. takahashi; Japan. J. Appl. ph.
ys. Vol.9, No8, pp.1006 (1970)).

[0005]

However, the above-mentioned conventional piezoelectric ceramics having a small mechanical quality factor Qm have an increased piezoelectric d constant for actuators and an increased electromechanical coupling factor K for broadband filters. In many cases, the main purpose is to reduce the Curie temperature and the heat resistance is insufficient.

[0006] Further, the conventional piezoelectric ceramic having a small mechanical quality factor Qm is formed at both ends of the piezoelectric ceramic even when the Curie temperature is high and the temperature rises in a soldering process or the like. It is good when the electrodes are short-circuited, but when the electrodes are opened, there is a problem that the electromechanical coupling coefficient K decreases and the resonance / anti-resonance frequency is largely shifted.

For this reason, when the conventional piezoelectric ceramic having a small Qm value is used as a surface-mount type filter element, the filter characteristics are greatly deteriorated when exposed to a high temperature (about 250 ° C.) in a reflow soldering process. There is a problem that.

In addition, Pb (Zr _0.52 Ti _0.48 ) O ₃ has M
n diffused material (M.Takahashi and S.takahashi;
Japan. J. Appl.phys.Vol.9, No8, pp.1006 (1970)
) Has a problem that the temperature characteristic of the resonance / anti-resonance frequency is poor, and is not suitable for use as a material for a filter element.

The present invention solves the above-mentioned problems, and is a piezoelectric ceramic having a small mechanical quality factor Qm value and excellent heat resistance. It is an object of the present invention to provide a piezoelectric ceramic for a filter element having a small distortion and capable of coping with surface mounting.

[0010]

In order to solve the above problems, a piezoelectric ceramic according to the present invention comprises a PbZr _1-x Ti _x O
₃ (where X = 0.45 to 0.54) 0.1 to 5.0 mol% of the Pb atom of the lead zirconate titanate represented by L
a, and up to 8 mol% of Pb atoms is
Mn is replaced with MnO ₂ with respect to a piezoelectric ceramic substituted with at least one selected from the group consisting of a, Sr, and Ba.
A piezoelectric ceramic containing 0.005 to 0.9% by weight in terms of Mn, wherein the Mn is contained by diffusion.
It is characterized by being.

Further, the piezoelectric ceramic according to the present invention is characterized in that the Mn
Are present at a higher concentration in the grain boundary layer than in the grains of the piezoelectric ceramic.

As described above, the piezoelectric ceramic according to the present invention is characterized in that the piezoelectric ceramic having a small mechanical quality factor Qm value and a high Curie temperature contains Mn to reduce the resistivity. Mn is diffused in a piezoelectric ceramic (for example, at a temperature of 900 to 1100 ° C.), and Mn is unevenly distributed so as to have a higher concentration in the grain boundary layer than in the inside of the grains, thereby lowering the resistivity. It is intended to be.

[0013]

For example, when a polarized piezoelectric ceramic is heated and returned to room temperature, pyroelectric charges are generated. The electric field due to the pyroelectric charge is generated in the direction opposite to the polarization direction of the piezoelectric ceramic, and reduces the magnitude of the polarization of the piezoelectric ceramic.

[0014] This invention is quickly extinguished the pyroelectric charge, to the magnitude of the polarization of piezoelectric ceramic is prevented from lowering, I der one which contains Mn in the piezoelectric ceramic, M
By diffusing n at a temperature of, for example, 900 to 1100 ° C., the resistivity of the piezoelectric ceramic is reduced, pyroelectric charges are rapidly discharged, and an electric field in the direction opposite to the polarization direction is applied for a long time. To prevent that .
This suppresses a decrease in the magnitude of the remanent polarization and reduces the amount of change in the resonance / anti-resonance frequency .
I'm trying .

[0015]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples of the present invention. First, PbO, SrCO ₃ , La ₂ O ₃ , TiO ₂ , ZrO ₂ ,
Are weighed so as to have a composition as shown in Table 1,
Water is added to this and wet-mixed using a ball mill. Then, after drying the mixture obtained by wet mixing, 8
The calcined material was calcined at 00 to 900 ° C for 2 hours, and the calcined material was wet-pulverized using a ball mill to obtain an adjusted powder.

Then, a binder such as water or polyvinyl alcohol is added to the prepared powder, press-molded, and baked at a temperature of 1150 to 1250 ° C. for 2 hours to obtain a circle having a diameter of 10 mm and a thickness of 1 mm. A plate-like porcelain was obtained. A paste prepared by kneading MnCO ₃ with a varnish is applied to the surface of the porcelain with a brush, dried,
The diffusion treatment was performed by heating at a temperature of 1100 ° C. for 2 hours.
Thereafter, the porcelain was polished to a thickness of 0.5 mm, and silver electrodes were baked on both end surfaces (both main surfaces). Then, polarization treatment was performed in an insulating oil at 80 ° C. for 30 minutes with an electric field of 2 to 3 kV / mm. A piezoelectric ceramic (oscillator sample) was obtained. For comparison,
Piezoelectric ceramics (vibrator samples) outside the scope of the present invention were produced in the same manner as in the above example.

For these samples, the specific resistance ρ, the electromechanical coupling coefficient Kp in radial vibration, the mechanical quality coefficient Qmp, and the temperature change rate (Fr−TC) of the resonance frequency Fr at −20 ° C. to 80 ° C. (Indicated as (temperature coefficient)).

The vibrator sample was placed in a thermostat at 250 ° C. for 3 hours.
After a heat treatment for a period of minutes, the electrode was taken out with both electrodes open, and then left for about 1 hour to measure changes ΔFr and ΔFa of the resonance frequency Fr and the antiresonance frequency Fa.

In the above embodiment, each characteristic (specific resistance ρ,
Table 1 shows the measurement results of the electromechanical coupling coefficient Kp, the mechanical quality coefficient Qmp, the temperature change rate (Fr-TC) of the resonance frequency Fr, and the change amounts ΔFr and ΔFa of the resonance frequency and the antiresonance frequency.

[0020]

[Table 1]

In Table 1, A, x, y, z, α
Are respectively the following formulas (1): Pb _{1 -XY} A _X La _Y Zr _{1 -Z}
Ti _Z O ₃ + α shows (wt%) of addition ratio and the components of the MnO ₂ ...... (1). That is, A is at least one of elements (Ca, Sr, and Ba) substituted with Pb.
Type), x indicates the ratio (mol%), and y
Indicates the ratio (mol%) of La. Z is Ti
(Mol%), and α indicates the Mn content ratio (% by weight).

In Table 1, those marked with an asterisk indicate piezoelectric ceramics (comparative examples) outside the scope of the present invention.

From the measurement results of each sample shown in Table 1 and other samples not shown in Table 1, A (Ca, S
It was found that when the substitution amount of (r, Ba) exceeds a total of 8 mol%, the Curie temperature is lowered, and the amounts of change ΔFr, ΔFa of the resonance / anti-resonance frequency after heating are increased, thereby deteriorating the heat resistance.

Further, when the La substitution amount y is less than 0.1 mol%, there is a problem that the temperature change rate Fr-TC of Fr becomes large, and the substitution amount y exceeds 5.0 mol%. It was found that the Curie temperature decreased and the heat resistance deteriorated.

Further, it was found that when the ratio z of Ti exceeds 54 mol%, the electromechanical coupling coefficient Kp decreases, and when the z ratio is less than 45 mol%, the Curie temperature decreases and heat resistance deteriorates. .

Also, from Table 1, a comparison between a sample outside the scope of the present invention (sample No. 1) and a sample according to the embodiment of the present invention (eg, sample No. 2) shows that the piezoelectric ceramic (sample no. .
2) shows that the specific resistance (resistivity) ρ is smaller by one digit or more than the sample containing no Mn (sample No. 1).

For sample No. 2, the elements present in the inside of the grain (FIG. 1, (A)) and in the grain boundary layer (FIG. 1, (B)) were analyzed using a transmission electron microscope. Analyzed by spectrum. The results are shown in FIGS. 2 and 3, respectively.

FIGS. 2 and 3 show that Mn contained by diffusion is distributed at a higher concentration in the grain boundary layer than in the grains of the piezoelectric ceramic (ceramics). That is, it can be seen that the specific resistance (resistivity) ρ of the piezoelectric ceramic was reduced due to Mn being unevenly distributed in the grain boundary layer of the piezoelectric ceramic.

As shown in Table 1, as a result of the decrease in the specific resistance ρ, it can be seen that the frequency changes ΔFr and ΔFa of the resonance frequency and the antiresonance frequency after heating are significantly reduced. Moreover, in this case, the mechanical quality factor Qmp is almost the same as that of the sample No. 1 containing no Mn, and the value of Kp is considerably larger than that of the sample No. 1. It can be seen that the characteristics have been improved.

When the added amount of Mn is less than 0.005% by weight in terms of MnO ₂ , the effect of improving characteristics such as specific resistance (resistivity) ρ and frequency variation ΔFr, ΔFa is insufficient. If it exceeds 0.9% by weight, the mechanical quality factor Qmp becomes large, or the frequency variation ΔFr, ΔF
a becomes large, so that Mn
Is preferably in the range of 0.005 to 0.9% by weight in terms of MnO ₂ .

[0031]

As described above, the piezoelectric ceramic of the present invention has the following features.
PbZr _1-x Ti _x O ₃ (where X = 0.45-0.5
0) of Pb atom of lead zirconate titanate represented by 4).
A piezoelectric ceramic obtained by substituting 1 to 5.0 mol% with La and further substituting up to 8 mol% of Pb atoms with at least one selected from the group consisting of Ca, Sr, and Ba: By diffusion, Mn is converted to MnO ₂ by 0.005.
０．９0.9% by weight, the electromechanical coupling coefficient K is large, and the temperature change rates of the resonance frequency and the antiresonance frequency and the mechanical quality coefficient Qm are small (for example, Qm = 100). Below) a piezoelectric ceramic can be obtained.

When the piezoelectric ceramic of the present invention is used for a ceramic filter (piezoelectric filter) element, the group delay time (GDT) characteristic is flat in a wide frequency band,
In addition, it is possible to exhibit the excellent characteristic that the phase distortion is small, and it is possible to make it difficult for a bit error to occur in the digital signal. Therefore, the piezoelectric ceramic of the present invention is particularly significant as a material for a digital-compatible piezoelectric filter element.

The piezoelectric ceramic according to the present invention is characterized in that the amount of change in the resonance frequency and the antiresonance frequency with respect to heating and cooling after heating is small. Therefore, even when the piezoelectric ceramic according to the present invention is used as a filter element material which is surface-mounted by reflow soldering or the like, characteristic deterioration due to high temperature (up to 250 ° C.), particularly shift of the pass band of the filter, and pass band The rate of decrease in width is small, and it is possible to sufficiently cope with surface mounting.

[Brief description of the drawings]

FIG. 1 is a photomicrograph (2) showing the crystal structure of a piezoelectric ceramic of sample No. 2 according to an embodiment of the present invention, taken by a transmission electron microscope.
0,000 times).

FIG. 2 is a view showing a characteristic X-ray spectrum inside a grain of a piezoelectric ceramic of Sample No. 2 according to an embodiment of the present invention.

FIG. 3 is a view showing a characteristic X-ray spectrum of a grain boundary layer of the piezoelectric ceramic of Sample No. 2 according to the embodiment of the present invention.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasunobu Yoneda 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Murata Manufacturing Co., Ltd. (56) References JP-A-5-163063 (JP, A) JP-A Heihei 5-116947 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/42-35/49 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] (1) PbZr _1-x Ti _x O ₃ (where X = 0.4
Pb of lead zirconate titanate represented by 5-0.54)
0.1 to 5.0 mol% of the atoms are replaced with La;
For a piezoelectric ceramic in which up to 8 mol% of Pb atoms are substituted with at least one selected from the group consisting of Ca, Sr, and Ba, Mn is converted to MnO ₂ in the range of 0.005 to 0.005.
A piezoelectric ceramic containing 0.9% by weight , wherein the Mn
Is characterized by being included by diffusion.
Piezoelectric ceramics . 2. The piezoelectric ceramic according to claim 1, wherein said Mn is present at a higher concentration in the grain boundary layer than in the grains of the piezoelectric ceramic.