JP2001048641A - Piezoelectric porcelain composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a piezoelectric porcelain composition which contains no lead and has a high mechanical quality factor by using, as constituent atoms or atomic groups of the composition, Bi, Na, TiO3 and LaFeO3 in specified compositional ratios, respectively. SOLUTION: This piezoelectric porcelain composition has a composition represented by the general formula (1-x)(Bi0.5Na0.5)TiO3-xLaFeO3 (wherein 0<x<=0.3) and is produced by using Bi2O3, Na2CO3, TiO2, La2O3 and Fe2O3, each having high chemical purity, as raw materials of the main constituents. The production process, for example, comprises: blending the above raw materials stoichiometrically with respect to the general formula to obtain a blend; mixing the blend in ethanol for 20 hr; maintaining the mixed material at 800 deg.C for 1 hr to calcine the mixed material; thereafter crushing the calcined material over a 10 hr period; granulating the crushed material with polyvinyl alcohol as a binder into granules; subjecting the granules to press forming under 1 ton/cm2 pressure into a disklike body having a 20 mm diameter and a 1 mm thickness; sintering the disklike body at 1,100-1,200 deg.C while maintaining the body at that temperature for 2 hr, to form a disklike sintered body; polishing the disklike sintered body so as to form its upper and lower parallel planes to each other; placing two silver electrodes on the upper and lower planes of the sintered body, respectively; and applying a DC electric field having a 4 kV/mm intensity to between the two silver electrodes in silicone oil maintained at 100 deg.C to effect a polarization in the thickness direction in the sintered body. Thus, the objective piezoelectric porcelain composition can be produced and applied to various piezoelectric devices such as filter and vibrator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a piezoelectric ceramic composition used for a wave device, a sensor, an actuator 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, taking measures to prevent them requires enormous costs for equipment installation. 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 and a filter requiring a high mechanical quality factor. It has been difficult to apply to applications such as vibrators.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and to provide a piezoelectric ceramic composition which is lead-free and has a high mechanical quality factor.

[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 -XLaFeO
_3. A piezoelectric ceramic composition represented by formula ₃ , wherein X is in the range of 0 <X ≦ 0.3.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Bi that is a degree₂O₃, Na₂CO₃, TiO ₂, La₂
O₃, Fe₂O₃Was used. These are represented by the general formula (1-X)
(Bi_0.5Na_0.5) TiO₃-XLaFeO
₃(0 ≦ X ≦ 0.4)
The mixture was mixed for 20 hours in ethanol by Lumil. this
Hold at 800 ° C for 1 hour and calcine, then pulverize for 10 hours
Was done. Uses polyvinyl alcohol as binder
Granulation, pressure 1ton / cm²20mm in diameter and thickness
It was press-formed into a 1 mm disk shape. Firing at a temperature of 1100
The temperature was maintained at で 1200 ° C. for 2 hours.

This sintered body was polished in parallel planes, silver electrodes were provided on the upper and lower surfaces thereof, and a DC electric field of 4 kV / mm was applied between the electrodes in silicone oil at 100 ° C. to polarize 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 —XLaFeO ₃ , 0 ≦ X ≦
Show k ₃₃ , kp, kt, Qm and ε ₃₃ ^t / ε ₀ in the range of 0.4. The blank at X = 0.4 is
This indicates that piezoelectricity could not be confirmed. FIG. 1 shows k ₃₃ , kp, and kt in the range of 0 ≦ X ≦ 0.35.

[0011]

[Table 1]

According to Table 1, Qm is maximum when X = 0.15.
Large value 472 is obtained, and (Bi _0.5Na_0.5)
TiO₃In contrast, it can be seen that Qm was improved. Only
However, in the range of X = 0 and 3 <X, Qm is not more than 300
It turns out that it is always small and difficult to put into practical use.

Further, from FIG. 1, k ₃₃ , kp and kt are not reduced in the range of 0 <X ≦ 0.3, whereas
When 3 <X, the value rapidly decreases. Therefore, 0 <X ≦
A range of 0.3 is considered suitable for practical use.

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

[0015]

As described above, according to the present invention,
A piezoelectric ceramic composition which is lead-free and has a high mechanical quality factor can be provided.

[Brief description of the drawings]

FIG. 1 is a general formula (1-X) (Bi _0.5 Na _0.5 ) T
_k 33 in the range of iO ₃ -XLaFeO ₃ in 0 ≦ X ≦ 0.35, kp, shows a kt.

[Explanation of symbols]

1 k ₃₃ 2 kp 3 kt

Claims (1)

[Claims] 1. A compound of the formula (1-X) (Bi _0.5 Na
_0.5 ) TiO ₃ —XLaFeO ₃ where X is 0 <
A piezoelectric ceramic composition, wherein X is in the range of 0.3.