JP2007217233A - Piezoelectric ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic with which specific dielectric constant is made small, mechanical quality coefficient Qm is made large, and electromechanical coupling factor is made large, and environmental problems due to lead do not occur. <P>SOLUTION: The piezoelectric ceramic is composed essentially of a ceramic expressed by general formula, (1-x-y)SrBi<SB>2</SB>Nb<SB>2</SB>O<SB>9</SB>-xNdBi<SB>2</SB>TiNbO<SB>9</SB>-yBi<SB>3</SB>TiNbO<SB>9</SB>, wherein (x) and (y) are in a range of 0<x<0.2 and 0<y<0.5, respectively, and 50-1,000 ppm by weight of ZrO<SB>2</SB>is added into the main component as an assistant component. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to piezoelectric ceramics used for ceramic resonators, ceramic filters, temperature sensors and the like.

Conventional piezoelectric ceramics include a PbZrO ₃ —PbTiO ₃ solid solution MPB (morphotropic phase boundary) neighborhood composition system called PZT. Piezoelectric ceramics having such a composition are inexpensive and have good electrical characteristics, and are therefore used in various electronic parts.
However, since this type of piezoelectric ceramic contains a large amount of lead, the lead is released into the atmosphere at the time of heat treatment such as firing and melting in the manufacturing process, or after being marketed in the form of electronic components, Even when parts are discarded, the influence of lead on the environment caused by the release of lead into the soil has become a problem, and industrial use has been prohibited or restricted.
In recent years, electrical signals have been rapidly converted from analog to digital, so the range of use of electronic components is expanding into the high frequency region, the relative dielectric constant is as small as 1000 or less, and the mechanical quality factor Qm is The demand for piezoelectric ceramics as large as 2000 or more is increasing.
Under such circumstances, bismuth layered structure ferroelectrics have attracted attention as a material that does not contain lead, has a low relative dielectric constant, and has a high mechanical quality factor Qm. (For example, see Patent Documents 1 and 2.)
JP 2002-145669 A JP 2001-294486 A

  However, the bismuth layer structure ferroelectric has a small relative dielectric constant and a small electromechanical coupling coefficient k even if the mechanical quality factor Qm is large.

  An object of the present invention is to provide a piezoelectric ceramic that can reduce the relative dielectric constant, increase the mechanical quality factor Qm, increase the electromechanical coupling coefficient k, and cause no environmental problems due to lead. And

The piezoelectric ceramic of the present invention is obtained by dissolving Sr—Bi—Nb ceramics, Nd—Bi—Ti—Nb ceramics, and Bi—Ti—Nb ceramics, which are a kind of bismuth layered structure ferroelectrics, as described above. It solves the problem.
The piezoelectric ceramic of the present invention are represented by the general formula _{(1-x-y) SrBi} 2 Nb 2 O 9 -xNdBi 2 TiNbO 9 -yBi 3 TiNbO 9, x is 0 <x <0.2, y is 0 < The main component is ceramics having a composition range of y <0.5, and ZrO ₂ is added as a subcomponent to the main component in an amount of 50 to 1000 ppm by weight.

The piezoelectric ceramic of the present invention are represented by the general formula _{(1-x-y) SrBi} 2 Nb 2 O 9 -xNdBi 2 TiNbO 9 -yBi 3 TiNbO 9, x is 0 <x <0.2, y is 0 < Addition of 50 to 1000 ppm by weight of ceramics in the composition range of y <0.5 as a main component and ZrO ₂ as a subcomponent to the main component, thereby reducing the relative dielectric constant and the mechanical quality factor Qm. And the electromechanical coupling coefficient k can be increased. Further, since the piezoelectric ceramic of the present invention does not contain lead, lead is not released when the manufacturing process or electronic parts are discarded, and environmental problems do not occur.

In the piezoelectric ceramic of the present invention, Nd—Bi—Ti—Nb ceramics and Bi—Ti—Nb ceramics are dissolved in Sr—Bi—Nb ceramics. The electromechanical coupling coefficient k can be adjusted by the solid solution amount of the Nd—Bi—Ti—Nb ceramics and the Bi—Ti—Nb ceramics. Further, the electromechanical coupling coefficient k can also be adjusted by the amount of ZrO ₂ added as a subcomponent.

Examples of the piezoelectric ceramic of the present invention will be described below.
First, a method for manufacturing a piezoelectric ceramic according to the present invention will be described. Raw material powders of SrCO ₃ , Bi ₂ O ₃ , Nb ₂ O ₅ , Nd ₂ O ₃ , TiO ₂ , and ZrO ₂ were weighed to have a predetermined composition, and wet-mixed for 20 hours using a ball mill or the like. These mixed powders were calcined at 750 to 1000 ° C., and the calcined product was pulverized so that the average particle size was 1 μm or less. After the pulverized product was dried, a binder was added thereto, granulated, molded and fired to obtain a material according to the present invention.

  The characteristics of the piezoelectric ceramic according to the present invention were measured by polishing a 6.9 mm × 6.9 mm square plate-shaped porcelain formed and fired from the above-described piezoelectric ceramic so that the thickness was 0.1 to 0.5 mm. Thereafter, silver electrodes are formed on both sides, and then in the insulating oil, once the polarization treatment is performed under the conditions of a temperature of 80 to 250 ° C., an electric field of 3 to 15 kV / mm, and a time of 1 to 30 minutes, the reverse direction Further, a circular electrode having a diameter of 0.5 to 1.5 mm was formed on a porcelain having a silver electrode etched, and an evaluation sample was obtained. This characteristic was measured using a resonance / anti-resonance method, and an electromechanical coupling coefficient k and a mechanical quality factor Qm of thickness longitudinal harmonic vibration having a frequency constant of about 4300 Hz · m were calculated.

a) FIG. 1 shows an evaluation sample prepared by examining the substitution amount x of NdBi ₂ TiNbO _{9 and} the substitution amount y of Bi ₃ TiNbO ₉ in the piezoelectric ceramic.
As a result, when the substitution amount x of NdBi ₂ TiNbO ₉ is 0 <x <0.2 and the substitution amount y of Bi ₃ TiNbO ₉ is 0 <y <0.5, the frequency constant is a thickness around 4300 Hz · m. The condition that the electromechanical coupling coefficient k and the mechanical quality factor Qm of the longitudinal harmonic vibration are maximized was obtained.
b) Next, FIG. 2 shows the results of measuring the characteristics when the amount of the ZrO2 raw material powder, which is a subsidiary component, is changed to the raw material powder obtained in a). However, the substitution amount x of NdBi ₂ TiNbO ₉ at this time was x = 0.065, and the substitution amount y of Bi ₃ TiNbO ₉ was y = 0.28. Sample No. The X mark indicates that it is outside the scope of the present invention.
As a result, the substitution amount x of NdBi ₂ TiNbO ₉ is 0 <x <0.2, the substitution amount y of Bi ₃ TiNbO ₉ is 0 <y <0.5, and the additive amount of ZrO 2 is 100 by weight. By setting the content within the range of ˜1000 ppm, the relative dielectric constant was 200 or less, the mechanical quality factor Qm was 2500 or more, and the electromechanical coupling coefficient k was 13% or more.

FIG. 3 shows frequency-impedance characteristics.
Waveform A is sample No. in FIG. 10 is a characteristic of the present invention, and the waveform B indicates the sample No. 8 is shown. Thus, it can be seen that the waveform A has a greater impedance characteristic than the waveform B, and the electromechanical coupling coefficient k and the mechanical quality factor Qm of the thickness longitudinal harmonic vibration having a frequency constant near 4300 Hz · m. Further, it can be seen that there is no spurious near the thickness longitudinal harmonic vibration having a frequency constant of about 4300 Hz · m, and energy confinement is possible.

Thus, in the piezoelectric ceramic of the present invention, the value of the substitution amount x of NdBi ₂ TiNbO ₉ is 0 <x <0.2, and the value of the substitution amount y of Bi ₃ TiNbO ₉ is in the range of 0 <y <0.5. By adding ZrO ₂ as a subsidiary component in the range of 50 to 1000 ppm by weight with respect to the main component, the relative dielectric constant is reduced, and an excellent electromechanical coupling coefficient k, mechanical quality factor Qm Can be obtained.

As mentioned above, although the Example of the piezoelectric ceramic of this invention was described, it is not restricted to these Examples. For example, the bismuth layered ferroelectric has only to have a main crystal structure, and a perovskite structure or a pyrochlore structure may be included as a sub-crystal structure in part. Further, instead of Nd of NdBi ₂ TiNbO ₉ , a rare earth metal such as La, Sm, Gd, or a composite thereof may be used.

The characteristics of the piezoelectric ceramic when the substitution amount x of NdBi ₂ TiNbO ₉ is 0 <x <0.2 and the substitution amount y of Bi ₃ TiNbO ₉ is 0 <y <0.5 are shown. It is a table | surface of the characteristic for demonstrating the characteristic of the piezoelectric ceramic of this invention. It is a frequency-impedance characteristic for demonstrating the characteristic of the piezoelectric ceramic of this invention.

Claims (1)

Formula _{(1-x-y) SrBi} 2 Nb 2 O 9 -xNdBi 2 TiNbO 9 -yBi 3 TiNbO 9
The main component is a ceramic having a composition range where x is 0 <x <0.2 and y is 0 <y <0.5, and ZrO ₂ as a subcomponent is 50 to 50 by weight with respect to the main component. Piezoelectric ceramics characterized by adding 1000 ppm.

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