JP2000143339A - Piezoelectric porcelain composition - Google Patents

Abstract

(57) [Problem] To provide a piezoelectric porcelain composition having a large piezoelectric property by using a lead-free material. SOLUTION: General formula, X (Bi _1-a Na _a ) TiO ₃ −
Represented by (1-X) LiNbO ₃ , where 0 <X <1, 0.3
In the composition range of ≦ a ≦ 0.7, practicable piezoelectric and dielectric properties (electromechanical coupling coefficients Kp, Kt, mechanical quality factor Q
m, the relative dielectric constant ε ₃₃ ^t / ε ₀ ).

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 used for electronic components such as wave devices, sensors and actuators.

[0002]

2. Description of the Related Art Conventionally, PZT (PbTiO ₃ -PbZrO ₃ ) -based ceramics composed of two components and PCM [PbTiO ₃ -P
_{bZrO 3 -Pb (Mg 0.5 Nb 0.5} ) TiO 3] based ceramics have been used mainly.

[0003] The reason for this is, of course, that the above-mentioned materials exhibit excellent piezoelectric properties, but other than that, when used in a wide variety of applications such as sensors, actuators, filters, etc., there is a demand for each application. This is because, in the above-described material system, the piezoelectric characteristics corresponding to the demand can be appropriately obtained by easily adjusting the ratio of each component amount in the above-mentioned material system.

[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 is highly volatile even at low temperatures,
In the sintering process, even small amounts may be released into the atmosphere.

[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.

Accordingly, as one of environmental measures, a material which does not contain lead and has a large piezoelectric characteristic has recently been demanded. Until now, piezoelectricity has been found in many lead-free materials, and among them, one-component (Bi _0.5 Na _0.5 )
TiO ₃ has an electromechanical coupling coefficient Kt of about 40%, which is in a practical range, but has a mechanical quality factor Qm of 250%.
There was a problem in practical use.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a piezoelectric ceramic composition which does not contain lead and has large piezoelectric characteristics.

[0008]

According to the present invention SUMMARY OF], a lead-free _{(Bi, Na) TiO 3 -LiNbO} 3 two-component system, a piezoelectric material having a practical piezoelectric characteristics can be obtained.

That is, the present invention provides a compound represented by the general formula: X (Bi _1-a N
_a a) TiO ₃ - represented by _{(1-X) LiNbO 3,} 0
<X <1, 0.3 ≦ a ≦ 0.7 A piezoelectric ceramic composition having a composition range of 0.7.

[0010]

Embodiments of the present invention will be described below.

As a raw material, a chemically pure Bi ₂
O ₃ , Li ₂ O ₃ , TiO ₂ , and Nb ₂ O ₅ were used. These are represented by the general formula X (Bi _1-a Na _a ) TiO _3- (1-X) L
It was blended in a stoichiometric ratio represented by iNbO ₃ (0 <X <1, 0.3 ≦ a ≦ 0.7) and mixed in ethanol by a ball mill for 20 hours. This was held at 800 ° C. for 1 hour, and after calcination, pulverization was performed for 10 hours. Granulate using polyvinyl alcohol as binder, pressure 1 to
It was pressed into a disk having a diameter of 20 mm and a thickness of 1 mm at n / cm ² . The firing was performed at a temperature of 1050 to 1200 ° 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 ° C. to polarize in the thickness direction. The piezoelectric and dielectric properties of these samples were measured. 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 characteristics were measured at a measurement frequency of 1 MHz using an LCR meter.

Table 1 shows X (B) according to the embodiment of the present invention.
_{i 0.5 Na 0.5) TiO 3 -} (1-X) LiNbO 3 (0 <
X <1), the piezoelectric and dielectric properties (electromechanical coupling coefficients Kp, Kt, mechanical quality factor Qm,
Relative dielectric constant ε ₃₃ ^t / ε ₀ ).

[0014]

As shown in Table 1, the addition of LiNbO ₃ increases the mechanical quality factor Qm.
The maximum value is 725 when = 0.6. In addition, the electromechanical coupling coefficient Kt increases to 42.8% at maximum when X = 0.7. The relative dielectric constants ε ₃₃ ^t / ε ₀ are also all low at 250 or less. Therefore, it was found that by adding LiNbO ₃ while keeping the characteristics of (Bi _0.5 Na _0.5 ) TiO ₃ , the characteristics which were a problem in practical use could be improved.

Table 2 shows the general formula X (Bi _1-a Na _a ) TiO _3- (1-X) LiNbO ₃ according to the embodiment of the present invention.
(0 <X <1, 0.3 ≦ a ≦ 0.7), X and a
And the dielectric properties (electromechanical coupling coefficients Kp, Kt, mechanical quality factor Qm, relative permittivity ε _{33) when the value of}
^t / ε ₀ ).

[0017]

[Table 2]

[0018]
In Table 2, when a is in the range of 0.3 to 0.7, no significant change in characteristics is observed, but in other ranges, the piezoelectric characteristics are significantly reduced. Also, when X was any other value, the characteristics were similarly reduced. Therefore, the composition range of the piezoelectric ceramic composition of the present invention is limited to 0.3 ≦ a ≦ 0.7.

[0019]

As described above, according to the present invention, as a measure against the environment, a lead-free piezoelectric material having a large piezoelectric characteristic, that is, a general formula, X (Bi _1- aN
_a a) TiO ₃ - In _{(1-X) LiNbO 3,} 0 <
A piezoelectric ceramic composition having a composition range of X <1, 0.3 ≦ a ≦ 0.7 can be provided.

Claims (1)

[Claims] 1. A compound represented by the general formula: X (Bi _1-a Na _a ) TiO ₃ −
Represented by (1-X) LiNbO ₃ , where 0 <X <1, 0.3
A piezoelectric ceramic composition having a composition range of ≦ a ≦ 0.7.