JP2000335967A - Piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the subject lead-free composition with high mechanical quality coefficient (Qm), being a specific compound composition comprising a Bi-Na-Ti-O-based component and a Bi-Cr-O-based component. SOLUTION: This piezoelectric ceramic composition is represented by the general formula: (1-x) (Bi0.5Na0.5)TiO3-xBiCrO3(0.03<=x<=0.3). This composition is obtained, for example, by the following process: using as the main component materials chemically high-purity Bi2O3, Na2CO3, TiO2 and Cr2O3, these materials are mutually formulated stoichiometrically based on the above general formula (wherein 0<=x<=0.4) and mixed together in ethanol for 20 h using a ball mill, the resulting mixture is held at 800 deg.C for one hour and then clacinated, and subsequently ground for about 10 h; the resulting ground product is granulated using polyvinyl alcohol as binder, subjected to pressure molding and then burnt to form a sintered compact as the objective composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric ceramic composition used for a wave device, a filter, a resonator, and the like.

[0002]

2. Description of the Related Art Conventionally, as a piezoelectric ceramic composition of this kind, PZT (PbTiO ₃ -PbZ) composed of two components has been used.
rO ₃ ) -based porcelain or PCM [PbTi
_{O 3 -PbZrO 3 -Pb (Mg 0.5} Nb 0.5) T
iO ₃ ] -based porcelain has been mainly used. The reason for this is, of course, that the above-mentioned composition exhibits large piezoelectricity, but at the same time, its applications are various, such as sensors, actuators and filters, and the characteristics required for each application are also various. On the other hand, in the above composition system, by adjusting the ratio of the amounts of the respective components, it is possible to appropriately operate to the characteristics corresponding to the requirements.

However, each of these compositions contains lead as a main component and has a raw material ratio of 60 wt% as lead oxide.
The above is also included. Lead oxide has high volatility even at low temperatures, and may be volatilized during production such as calcination or sintering, or may be eluted from industrial waste. However, this measure requires enormous costs for installation of the equipment. Therefore, there is a demand for a material that is lead-free and that exhibits large piezoelectric characteristics.

An existing lead-free piezoelectric ceramic composition, a general formula (Bi _0.5 Na _0.5 ) TiO ₃ , has a low mechanical quality factor Qm and a filter that requires a high Qm.
It has been difficult to apply it to applications such as resonators.

[0005]

An object of the present invention is to solve the above-mentioned problems and to provide a lead-free piezoelectric ceramic composition having a high Qm.

[0006]

According to the present invention, there is provided a compound represented by the general formula (1-
_{X) (Bi 0.5 Na 0.5)} TiO 3 -XBiCrO
_3. A piezoelectric ceramic composition represented by formula ₃ , wherein X is in the range of 0.03 ≦ X ≦ 0.3.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Bi that is a degree₂O₃, Na₂CO₃, TiO ₂, Cr₂
O₃Was used. These are represented by the general formula (1-X) (Bi_0.5
Na_0.5) TiO₃-XBiCrO₃(0 ≦ X ≦ 0.
4) is stoichiometrically compounded, and is
Mix in knoll for 20 hours. One hour at 800 ° C
It was calcined while holding, and then pulverized for 10 hours. Vine
Granulation using polyvinyl alcohol as the
ton / cm²Into a disc with a diameter of 20mm and a thickness of 1mm
It was molded under pressure. The firing is performed at a temperature of 1050 to 1150 ° C for 2 hours.
It was held for a while.

A silver electrode is provided on both sides of the sintered body,
A direct current voltage of 4 kV / mm was applied between the electrodes in silicone oil at ℃ to polarize the sintered body in the thickness direction.

Then, the piezoelectric and dielectric properties of these samples were measured. The piezoelectric characteristics, using a LF impedance analyzer, resonant - electromechanical coupling coefficient _k 33, kp, kt, the mechanical quality factor Qm was calculated by antiresonance method, and evaluated. The dielectric properties were measured at a frequency of 1 MHz using an LCR meter, and the relative permittivity ε ₃₃ ^t / ε was measured.
_It was rated ₀ .

Table 1 shows that (1-X) (Bi _0.5 Na
_0.5 ) In TiO ₃ —XBiCrO ₃ , 0 ≦ X ≦
Show k ₃₃ , kp, kt, Qm and ε ₃₃ ^t / ε ₀ in the range of 0.4.

[0011]

[Table 1]

In Table 1, Qm has a maximum value of 1288 when X = 0.2, and (Bi _0.5 Na _0.5 ) TiO
_In contrast to ₃ , it was confirmed that Qm was significantly improved. However, outside the range of 0.03 ≦ X ≦ 0.3, Qm
Was very small at 700 or less, which proved difficult to put into practical use.

In the range of 0.03 ≦ X ≦ 0.3,
The values of k ₃₃ , kp, and kt also increased, indicating that they were suitable for practical use.

From the above, (Bi _0.5 Na _0.5 ) Ti
By dissolving ₃ to 30 mol% of BiCrO ₃ in O ₃ , k _{33 of} (Bi _0.5 Na _0.5 ) TiO ₃ ,
Qm can be improved without deteriorating kp and kt. This enables application to applications such as filters and resonators.

[0015]

As described above, according to the present invention,
A lead-free piezoelectric ceramic composition having a high Qm could be provided.

Claims (1)

[Claims] 1. A compound of the formula (1-X) (Bi _0.5 Na
_0.5) is represented by _{TiO 3} -XBiCrO 3, X is 0.
A piezoelectric ceramic composition characterized by satisfying the following condition: 03 ≦ X ≦ 0.3.