JP2002145669A - Piezoelectric porcelain composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a Bi2SrNb2O9 based piezoelectric porcelain composition having a high coupling coefficient Kt and a high mechanical quantity coefficient Qm. SOLUTION: This piezoelectric porcelain composition consists of a bismuth layered compound expressed by Bi2(Sr1-XMX)Nb2O9 (wherein, M is Y or La, and 0<X<=0.4). Also, Mn is added by <=1.5 wt.% (not zero) expressed in terms of MnO2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition used for various piezoelectric devices.

[0002]

2. Description of the Related Art Piezoelectric ceramic compositions include ceramic filters,
It is widely used in oscillators, sound generators, actuators, etc., and requires large piezoelectricity.
bTiO ₃ and lead zirconate titanate Pb (TiZr) O ₃
Is used as the main component.

[0003]

However, in recent years, there has been a demand for the development of a lead-free piezoelectric ceramic composition in which lead has been eliminated from consideration of the global environment, and bismuth layered perovskite, non-lead group IV perovskite, non-lead II Although much research has been carried out, such as group IV perovskite, practically no piezoelectric properties have been obtained and hardly mass-produced.

One promising lead-free piezoelectric ceramic composition is a bismuth layered perovskite compound of Bi ₂ SrNb ₂ O ₉ . This is 250 ° C due to high Curie point
It withstands high temperatures and has a practical frequency temperature characteristic of -30 ppm. However, the piezoelectricity has a coupling coefficient Kt of 10
%, About 1/5 of the lead-based piezoelectric ceramic composition, and the mechanical quality factor Qm is about 900, which is not practical.

On the other hand, when used as a ceramic filter or an oscillator, the mechanical quality factor Qm is an important factor in addition to the electromechanical coupling factor Kt. The mechanical quality factor Qm is a constant related to the ratio of the impedance at the resonance frequency and the anti-resonance frequency, and largely affects the signal processing capability of the circuit used (gain and attenuation). The large mechanical quality coefficient Qm can sufficiently compensate for the small coupling coefficient Kt. For this purpose, the coupling coefficient Kt
In particular, those having a mechanical quality factor Qm of 2000 or more have been desired.

An object of the present invention is to solve the above-mentioned conventional problems and to provide a piezoelectric ceramic composition having a practical value by greatly improving the mechanical quality factor Qm together with the coupling coefficient Kt. is there.

[0007]

To achieve the above object, the present invention has the following arrangement.

[0008] According to a first aspect of the present invention have the general formula _{Bi 2 (Sr 1-X M} X) Nb 2 O 9 comprising bismuth layer compound (where M is Y or La) is represented by, X is 0 <X ≦
It is a piezoelectric ceramic composition having a value of 0.4 and containing 1.5 wt% or less (excluding 0) of Mn in terms of MnO ₂ , and simply replacing Sr with Y or La results in a coupling coefficient Kt. Shows little change, but by adding Mn to this, the coupling coefficient Kt and the mechanical quality factor Qm
The effect of increasing both is obtained. At this time, the range of X is 0 to 0.4 (excluding 0), and Mn is 1.5 w
The reason why the content is set to t% or less (excluding 0) is that a remarkable effect cannot be obtained in the other range.

According to a second aspect of the present invention, there is provided a piezoelectric ceramic composition wherein at least one of Nb and Cr is added to the composition according to the first aspect. Requires a polarization treatment at 180 to 200 ° C., so that there are also problems in selection of heat-resistant materials for the polarization jig, thermal decomposition of insulating oil, and mass productivity such as work efficiency. The addition of at least one of Nb (this element is also a constituent element of the general formula and results in an excess of the stoichiometric composition) or Cr can significantly reduce the polarization treatment temperature to 100 to 140 ° C. This makes it possible to provide porcelain with good mass productivity. At this time, the Nb content is set to 5 wt% or less and the Cr content is set to 0.5 wt% or less based on the total weight, because in other ranges, the resistance of the porcelain decreases and the polarization treatment cannot be performed.

According to a third aspect of the present invention, the amount of Nb added in excess of 5 wt% in terms of Nb ₂ O ₅ is added to the composition of the first aspect. It specifies the amount.

According to a fourth aspect of the present invention, the amount of Cr to be added is 0.5 wt% or less in terms of Cr ₂ O ₃ added to the composition of the first aspect. It specifies the amount.

[0012]

(Embodiment 1) First, Bi ₂ O ₃ , SrCO ₃ , Nb ₂ O ₅ , Cr ₂ O ₃ , Y _{2 are used} as starting materials.
O ₃ and La ₂ O ₃ were weighed so as to have the compositions shown in (Table 1) and (Table 2), and were wet-mixed using a ball mill for 16 hours and dried.

[0013] Next, the dried mixed raw material is
After calcination at a temperature of 0 ° C. for 2 hours, use a ball mill again for 1 hour.
A piezoelectric material was produced by wet grinding and drying for 6 hours.

Next, 8% to 12% by weight of a 5% polyvinyl alcohol solution as a binder is added to the piezoelectric material, and the resultant is granulated. To 1550 to 1
Sintering was performed at a temperature of 250 ° C. to produce a sintered body of a piezoelectric element.

After the obtained sintered body is polished to a thickness of 0.5 mm, a silver electrode paste is applied to both sides and dried.
Baking was performed at a temperature of 700 ° C.

Next, after a DC voltage of 3.5 KV (7 KV / mm) is applied in silicon oil at each temperature raised from 100 ° C. to 200 ° C. in steps of 20 ° C. to perform polarization, the coupling coefficient of each sample is increased. Kt and mechanical quality factor Qm were measured. Thereafter, a sample considered to be the saturation polarization treatment temperature was selected, and the results are shown in (Table 1) and (Table 2).

[0017]

[Table 1]

[0018]

[Table 2]

The coupling coefficient Kt and the mechanical quality factor Q
“m” is ESMA-6100 which is a standard of the Electronic Materials Industry Association.
(Electrical test method of piezoelectric ceramic vibrator) was measured and calculated. In addition, when selecting the value of each sample, the sample was measured at six points between 100 ° C. and 200 ° C. in a range where the coupling coefficient Kt did not decrease by 5% or more based on the point where the coupling coefficient Kt became the maximum. The value of the lowest polarization treatment temperature is defined as the saturation polarization treatment temperature, and the value at this point is described in the table.

Table 1 shows the basic composition of the present invention in which the bismuth layered compound is substituted with Y or La and the characteristic values thereof, and Table 2 shows that the composition of the present invention contains an excess of Nb or C.
The composition and the characteristic value to which r was added.

As shown in Table 1, the conventional composition (Sample No. 1) has a coupling coefficient Kt of about 12% and a mechanical quality coefficient Qm of about 900, and is used for a ceramic filter or an oscillator. Has been practically difficult due to the complexity. On the other hand, Sr was replaced with Y or La (sample numbers 3, 4, 5, 8, 9, 10, 1).
5,16,17,20,21,22) improve the coupling coefficient Kt to 13 to 20% and at the same time, improve the mechanical quality factor Qm.
It can be seen that the value greatly increases to 2000 to 8000.
This results in a practical piezoelectric ceramic composition.

Here, when Y or La exceeds 0.4 (sample numbers 12, 13, 24, 25), or when Mn exceeds 2 wt% (sample numbers 6, 11, 18, 2).
3) Although the mechanical quality factor Qm is 1000 to 1500, which is larger than that of the conventional composition, the practical effect is lost if the coupling coefficient Kt is reduced and both are taken into account. Also, Mn
Is not added (Sample Nos. 2 and 14), the level is almost the same as the conventional composition, and no effect is observed.

As shown in Table 2, the composition of the present invention further contained excess Nb (Sample Nos. 26, 27, 28, 35, 3).
6, 37) or Cr (sample numbers 30, 31, 32,
39, 40, 41) can significantly lower the polarization treatment temperature to 100 to 140 ° C. while maintaining the coupling coefficient Kt and the mechanical quality factor Qm at high levels. By adding this, a piezoelectric ceramic composition which can be easily mass-produced is obtained. This means that even if Nb and Cr are added simultaneously (Sample No. 34), the useful effect does not change.

At this time, if the Nb content exceeds 5 wt% (sample Nos. 29 and 38), sintering of the porcelain becomes difficult,
Exceeds 0.5 wt% (Sample Nos. 33 and 42), the insulation resistance is reduced beyond the limit, so that the polarization treatment cannot be performed.

[0025]

As described above, according to the present invention _{Bi 2 (Sr 1-X M} X) Nb 2
O ₉ (M is Y or La, 0 <X ≦ 0.4) Mn
Is added (1.5 wt% or less), the coupling coefficient Kt,
It can be seen that this is an excellent piezoelectric ceramic composition having a large mechanical quality factor Qm. In addition, excessive Nb (5w
(t% or less) or Cr (0.5 wt% or less) lowers the polarization treatment temperature to produce a piezoelectric ceramic composition which can be easily mass-produced.

Claims (4)

[Claims] 1. A general formula _{Bi 2 (Sr 1-X M} X) Nb 2 O 9
(Where M is Y or La, 0 <X ≦ 0.4), and Mn is Mn.
O ₂ in terms of less 1.5 wt% piezoelectric ceramic composition containing an amount of (excluding 0). 2. The piezoelectric ceramic composition according to claim 1, wherein at least one of Nb and Cr is added. 3. The amount of Nb is 5 wt% in terms of Nb ₂ O _5.
The piezoelectric ceramic composition according to claim 1, which is: 4. The amount of Cr is 0.5 w in terms of Cr ₂ O _3.
The piezoelectric ceramic composition according to claim 1, which is at most t%.