JP2000272962A - Piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a material for a suitable piezoelectric ceramic element without using Pb by using a specific composition of Bi, Na, K and TiO2. SOLUTION: The objective composition is expressed by the general formula [Bi0.5(Na1-xKx)0.5]TiO3 wherein (x) is a molar ratio satisfying the formula 0.20<x<=0.30. The composition can be produced by using highly pure Bi2O3, Na2CO3, TiO2 and K2CO3 as main component raw materials and <=2 wt.% additives such as Fe2O3 and Cr2O3, stoichiometrically mixing the components to get the above composition, mixing in ethanol for about 20 hr with a ball mill, calcining the mixture by keeping at about 800 deg.C for 1 hr, crushing for about 10 hr, granulating the powder using a polyvinyl alcohol as a binder, compression molding in the form of a disk having a prescribed dimension and baking the molded disk by keeping at about 1100 deg.C for about 2 hr.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric porcelain composition particularly suitable for electronic components such as wave devices, sensors and actuators.

[0002]

Conventionally, as the piezoelectric material, and a two-component _PZT (PbTiO 3 -PbZrO ₃₎ ceramics and, PCM consists of three components [PbTiO _{3
-PbZrO 3 -Pb (Mg 0.5 Nb 0.5} ) TiO
₃ ] series ceramics have been mainly used.

[0003] The reason for this is, of course, that the above-mentioned materials exhibit excellent piezoelectric properties.
This is because, when used in a wide variety of applications such as sensors, actuators, and filters, the characteristics required for each application are various, and the piezoelectric characteristics corresponding to the requirements can be obtained appropriately.

[0004]

However, the above-mentioned conventional piezoelectric materials have the following disadvantages. That is, the main component of these materials is lead oxide, which contains 60 wt% or more. Lead oxide has high volatility even at low temperatures, and may be released into the atmosphere even in a small amount in the calcining and sintering steps.

[0005] It is also conceivable that the substance is eluted from industrial waste. Another major problem is that huge investments must be made in capital investment for these measures.

[0006] Therefore, the present invention does not contain lead, and
An object of the present invention is to provide a piezoelectric ceramic composition that can be used as a material for a piezoelectric ceramic element.

[0007]

According to the present invention, this problem is solved.
As a means to solve the problem, lead-free [Bi
_0.5(Na_1-xK_x)_0.5TiO₃System
As a result, a piezoelectric material having practical piezoelectric properties is obtained.
You.

That is, the present invention relates to a compound represented by the general formula [Bi _0.5 (N
a _1-x K _x ) _0.5 ] TiO ₃ , the molar ratio x
Is in the range of 0.20 <x ≦ 0.30.

Further, the present invention provides the above-mentioned piezoelectric ceramic composition.
However, as an additive, Fe₂O₃, Cr ₂O₃, Mn
O₂, NiO, Co₂O₃, La₂O₃, BaCO₃,
Sb₂O₃, Nb₂O₅At least one of them is 2w
This is a piezoelectric ceramic composition containing t% or less.

[0010]

Embodiments of the present invention will be described below.

(First Embodiment) First, the first embodiment of the present invention will be described.
An embodiment will be described. Bi ₂ O ₃ , Na ₂ CO ₃ , TiO which are chemically high purity
₂ , K ₂ CO ₃ was used.

These are represented by the general formula [Bi _0.5 (Na _{1-x
K x) 0.5] TiO 3 (} 0.1 ≦ x ≦ 0.5) + additives (hereinafter 2 wt%) with respect to stoichiometric formulations were mixed in ethanol for 20 hours by a ball mill.

This is kept at 800 ° C. for 1 hour and calcined.
Next, grinding was performed for 10 hours. Granulated using polyvinyl alcohol as binder, pressure 1 ton / cm ²
To form a disc having a diameter of 20 mm and a thickness of 1 mm.
The firing was performed at a temperature of 1100 ° C. for 2 hours.

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 in the thickness direction.

[0015] The piezoelectric and dielectric properties of these samples were measured. For the piezoelectric measurement, an electromechanical coupling coefficient and a mechanical quality coefficient were calculated by a resonance-antiresonance method using an LF impedance analyzer. The dielectric properties are
The measurement was performed at a measurement frequency of 1 MHz using an LCR meter.

Table 1 shows [Bi according to the embodiment of the present invention.
_0.5(Na_xK_1-x)_0.TiO₃(X: 0.1
~ 0.5) Piezoelectric and dielectric properties of the piezoelectric ceramic composition
Characteristics (electromechanical coupling coefficient k₃₃, K_p, K_t, Mechanical goods
Quality factor Q_m, Relative permittivity ε₃₃ ^t/ Ε₀).

[0017]

[Table 1]

As shown in Table 1, x ranges from 0.21 to 0.30.
It was confirmed that the relative permittivity and the electromechanical coupling coefficient had the maximum values in the range of. Its value is 42.3% in the _{k t, ε 33}
1033 at ^t / ε ₀ and (Bi _0.5 Na _0.5 ) Ti
_{O 3 (k t = 41.8%} , ε 33 t / ε 0 = 82) as compared to, a large value relative dielectric constant was obtained. Outside the above range, the electromechanical coupling coefficient is small and is considered unsuitable for practical use.

Further, as a result of investigation by X-ray diffraction, it was confirmed that a crystal structure phase boundary between rhombohedral and tetragonal crystals was present in the range. This is similar to the PZT-based porcelain having a maximum piezoelectric property at a structural phase boundary.

(Second Embodiment) Next, a second embodiment of the present invention will be described.
An embodiment will be described. As a main ingredient material
Bi with high purity₂O₃, Na₂CO₃, TiO
₂, K₂CO₃And high-purity Fe as an additive
₂O₃, Cr₂O₃, MnO₂, NiO, Co₂O ₃,
La₂O₃, BaCO₃, Sb₂O₃, Nb₂O₅For
Was. The sample preparation method and the measurement method are the same as those in the first embodiment.
Performed in the same manner.

Table 2 shows that [Bi _0.5 (Na _0.79 K
_0.21 ) _0.5 ] Fe ₂ O ₃ , Cr on TiO _{3
2 to 3} wt% of ₂ O ₃ , NiO, MnO ₂ , Co ₂ O ₃
Piezoelectric and dielectric characteristics when each added shown (electromechanical coupling coefficient _{k 33, k p, k t} , the mechanical quality factor _{Q m,} the dielectric constant ε ₃₃ ^t / ε ₀₎ and.

[0022]

[Table 2]

As shown in Table 2, each additive was 2 wt.
Up to the% addition, the mechanical quality factor Qm was dramatically improved.
In addition, an electromechanical coupling coefficient was equivalent to that in the case without addition.

However, when added more, a decrease in the electromechanical coupling coefficient was observed. Therefore, Fe ₂ O ₃ , Cr ₂
O ₃ , NiO, MnO ₂ , and Co ₂ O ₃ are each 2w
By adding t%, the mechanical quality factor Qm can be improved, and characteristics applicable to uses such as a filter and a vibrator can be obtained.

Table 3 shows [Bi_0.5(Na_0.75K
_0.25)_0.5TiO₃And La ₂O₃, BaCO
₃, Sb₂O₃, Nb₂O₅1 to 3 wt% each
Piezoelectric and dielectric properties (electromechanical coupling coefficient
k₃₃, K_p, K_t, Mechanical quality factor Q_m, Relative permittivity ε
₃₃ ^t/ Ε₀).

[0026]

[Table 3]

As shown in Table 3, each additive was 2 wt.
%, The electromechanical coupling coefficient and the relative permittivity ε ₃₃ ^t
/ Ε ₀ was confirmed to be dramatically improved. However, if it is added more, a remarkable decrease in the electromechanical coupling coefficient is observed, which is not suitable for practical use. Therefore, La ₂ O ₃ , BaCO ₃ , S
By adding each of b ₂ O ₃ and Nb ₂ O _{5 up} to 2 wt%, characteristics applicable to applications such as actuators where a high dielectric constant and a high electromechanical coupling coefficient are desired are obtained.

[0028]

As described above, according to the present invention, as an environmental measure, a lead-free piezoelectric material having large piezoelectric characteristics can be obtained. Further, an effect that can be applied to a filter, a vibrator, or an actuator, for which a high dielectric constant is desired, where a high mechanical quality factor Qm is desired can be expected.

Claims (2)

[Claims] [Claim 1] The general formula [Bi _0.5 (Na _1-x K _x )]
_0.5 ] TiO ₃ and the molar ratio x is 0.20 <x
A piezoelectric ceramic composition characterized by being in the range of ≦ 0.30. 2. The method according to claim 1, wherein the piezoelectric ceramic composition is an additive.
And Fe₂O₃, Cr ₂O₃, MnO₂, NiO, Co
₂O₃, La₂O₃, BaCO₃, Sb₂O₃, Nb₂
O₅That at least one of them contains 2 wt% or less.
The piezoelectric ceramic composition according to claim 1, wherein: