JP2004238263A - Piezoelectric ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic that solves a problem of adverse effects of lead to environment due to its lead containment in a large amount and also that solves a problem of being not applicable to electronic components used at a high frequency band due to its large dielectric constant and small mechanical quality factor. <P>SOLUTION: The piezoelectric ceramic is comprised of a ceramic represented by general formula:Sm<SB>x</SB>Bi<SB>3-x</SB>TiNbO<SB>9</SB>(wherein, x is a compositional range of 0<x≤0.6) as a main component. The piezoelectric ceramic can be easily polarized and can be accomplished in that the dielectric constant becomes small and the mechanical quality factor Qm becomes large. Also, the problem of environment by lead is solved. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a piezoelectric ceramic used for a ceramic resonator, a ceramic filter, a temperature sensor, and the like.
[0002]
[Prior art]
As a conventional piezoelectric ceramic, there is a PbZrO ₃ -PbTiO ₃ solid solution called PZT having a composition near the MPB (morphotropic phase boundary). Piezoelectric ceramics having such a composition are used for various electronic components because they are inexpensive and have good electric characteristics.
However, since this kind of piezoelectric ceramics contains a large amount of lead, lead is released into the atmosphere during heat treatment such as sintering and melting in the manufacturing process, or after being marketed in the form of electronic components, Even when these electronic components are discarded, lead is released into the soil and the effect of lead on the environment becomes a problem, and industrial use has been prohibited or restricted.
In recent years, the conversion of electric signals from analog to digital has been rapidly performed, and the use range of electronic components has been expanding to a high frequency range. However, the above-described piezoelectric ceramics cannot be used for electronic components used in a high frequency band because the relative dielectric constant is as large as 1000 or more and the mechanical quality factor Qm is as small as 2500 or less.
In such a situation, a bismuth layered ferroelectric has attracted attention as a material that does not contain lead, has a small relative dielectric constant, and has a large mechanical quality factor Qm.
[0003]
[Problems to be solved by the invention]
However, bismuth layered ferroelectrics are generally difficult to polarize, and it has been difficult to obtain sufficient piezoelectric characteristics. For example, Bi ₃ TiNbO ₉ , a type of bismuth layered structure ferroelectric, is difficult to sufficiently polarize, and is disclosed in JP-A-2002-173369 and Kiyoshi Okazaki, “Third Edition Ceramic Dielectric Engineering,” As described in Gakudonsha, 1983.6.10, p501, there were almost no reports on piezoelectric characteristics.
[0004]
An object of the present invention is to provide a piezoelectric ceramic which can be easily polarized, has a small relative dielectric constant, can have a large mechanical quality factor Qm, and does not cause environmental problems due to lead.
[0005]
[Means for Solving the Problems]
The piezoelectric ceramic of the present invention solves the above-mentioned problem by improving the composition of Bi ₃ TiNbO ₉ , which is a kind of bismuth layered structure ferroelectric.
The piezoelectric ceramic of the present invention are represented by the general formula _{Sm x Bi 3-x TiNbO 9} , mainly composed of ceramics x is in the composition range of 0 <x ≦ 0.6.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
By substituting a part of Bi of Bi ₃ TiNbO ₉ with Sm, the electric field required for polarization becomes smaller, and polarization becomes easier than before. As a result, the mechanical quality factor Qm is improved.
[0007]
【Example】
Hereinafter, examples of the present invention will be described.
First, a method for manufacturing a piezoelectric ceramic according to the present invention will be described. Raw material powders of Sm ₂ O ₃ , Bi ₂ O ₃ , Nb ₂ O ₅ , and TiO ₂ were weighed to have a predetermined composition, wet-mixed using a ball mill or the like for 7 hours, and then wet-pulverized. After the pulverized product was dried, a binder such as PVA was added to the pulverized product, granulated, molded, and fired to obtain a material according to the present invention.
[0008]
The characteristics of the piezoelectric ceramics according to the present invention are measured by adding a binder such as PVA to the dried pulverized material in an amount of 1 to 3% by weight and granulating the dried pulverized material into a disk having a diameter of 15 mm and a thickness of 1 to 2.5 mm. Press molding at a pressure of 100 MPa, baking so that the maximum holding temperature is 1100 to 1300 ° C., and the holding time at the maximum holding temperature is 2 hours, to obtain a disc-shaped porcelain, and the disc-shaped porcelain having a thickness of Is 0.2 to 2 mm, and silver electrodes are formed on both surfaces. Then, in an insulating oil, the temperature is 100 to 250 ° C., the electric field is 5 to 12 MV / m, and the time is 1 to 30 minutes. An evaluation sample was obtained by performing a polarization treatment under the following conditions. For the measurement of this characteristic, the electromechanical coupling coefficient Kt and the mechanical quality coefficient Qm of the thickness longitudinal fundamental vibration were calculated using the resonance / antiresonance method. Further, the temperature change of the relative dielectric constant was measured, and the Curie temperature Tc was calculated. Further, in the polarization process, the electric field (ie, polarization electric field) when the disk-shaped porcelain was polarized was measured.
[0009]
_1, in the _{Sm x Bi 3-x TiNbO 9} , the electromechanical coupling coefficient Kt of the thickness extensional fundamental vibration when changing the substitution amount x of Sm, mechanical quality factor Qm, polarization field (MV / m), Curie The temperature Tc and the firing temperature are summarized in a table. In addition, * mark of a sample No has shown that it is out of the range of the present invention.
The piezoelectric ceramic of the present invention had a mechanical quality factor Qm of 6000 or more and a relative dielectric constant of 200 or less when the substitution amount x of Sm was in the range of 0 <x ≦ 0.6. In the case where the substitution amount x of Sm is 0 (ie, the conventional one), dielectric breakdown occurred without polarization. However, as the substitution amount x of Sm was increased, the electric field required for polarization (that is, the polarization electric field) was increased. Tended to be smaller. When the substitution amount x of Sm was set to 1, the sinterability was reduced, and the dielectric breakdown occurred without polarization.
Also, when the replacement amount x of Sm is increased, the Curie temperature Tc tends to decrease, but the electronic component is in a state sufficiently higher than the reflow temperature at the time of soldering an electronic component to a printed circuit board of an electronic device. There is no depolarization by attaching.
[0010]
Thus, when the substitution amount x of Sm is in the range of 0 <x ≦ 0.6, a good mechanical quality factor Qm can be obtained, and the polarization electric field and the relative dielectric constant can be reduced.
[0011]
In the embodiment, Bi in Ti ₃ NbO ₉ is partially replaced with Sm, but Bi may be replaced with a rare earth metal such as La, Nd or Gd.
[0012]
【The invention's effect】
The piezoelectric ceramic of the present invention are represented by the general formula _{Sm x Bi 3-x TiNbO 9} , since the main component ceramics x is in the composition range of 0 <x ≦ 0.6, it is possible to easily polarized At the same time, the relative dielectric constant can be reduced and the mechanical quality factor Qm can be increased. In addition, since the piezoelectric ceramic of the present invention does not contain lead, lead is not released during the manufacturing process or when electronic components are discarded, and there is no environmental problem.
[Brief description of the drawings]
FIG. 1 is a table of characteristics for explaining characteristics of a piezoelectric ceramic of the present invention.

Claims (1)

Formula _Sm x _Bi 3-x TiNbO ₉
Wherein x is in the composition range of 0 <x ≦ 0.6 as a main component.

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