JP2001302343A - Piezoelectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition, which is a lead-free piezoelectric material and has high mechanical quality factor. SOLUTION: At least one or more kinds of Fe2O3, Cr2O3, MnO2, NiO and Co2O3 are incorporated by <=2.0 wt.% in total in a ceramic expressed by a general formula, A2+5XBi4-5X(Ti1-XNbX)5O18 (A: at least one kind of Ba, Sr and Ca, 0<=X<0.3).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

Conventionally, piezoelectric composed of two components as a ceramic composition _PZT (PbTiO 3 -PbZrO ₃₎ based porcelain or PCM consists of three components _[PbTiO 3 -PbZ
rO ₃ (Mg _0.5 Nb _0.5 ) TiO ₃ ] -based porcelain has been mainly used. The reason for this is, of course, that the above-mentioned materials exhibit great piezoelectricity, but the following can also be mentioned. The applications of piezoelectric materials cover a wide variety of applications, such as sensors, actuators, and filters, and the characteristics required for each application are also diverse. This is because it is possible to appropriately operate according to the determined characteristics.

However, the main components of these materials are all
It is mainly composed of lead.
More than 60 wt% is contained. Lead oxide is volatile even at low temperatures.
Highly spontaneous and can be released into the atmosphere during calcination, sintering, etc.
There is a potential. Also consider elution from industrial waste.
available. In order to take this measure, it is necessary to install equipment.
You have to spend a lot of money. Therefore, lead-free materials
Materials that exhibit large piezoelectric characteristics are demanded.
Piezoelectricity has been found in many lead-free materials. For example, (B
i_0.5Na_0.5) TiO_Three, Bi layered compounds. Only
And the composition (Bi _0.5Na_0.5) TiO_ThreeIs an electromechanical coupling
The coefficient Kt was in the practical range of about 40%.
The mechanical quality factor Qm is as low as about 250. On the other hand, Bi layer
The compound has a high mechanical quality factor but an electromechanical coupling factor of 3
There is a problem such as 0% or less, so it cannot be put to practical use
Was.

Therefore, the mechanical quality factor Qm is 1900
In addition, there is a demand for an electromechanical coupling coefficient Kt of 30% or more.

[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 a lead-free piezoelectric material and has a high mechanical quality factor.

[0006]

The present invention provides a compound represented by the general formula A:
_{2 + 5X} Bi _4-5X (Ti _1-X Nb _X ) ₅ O
₁₈ (A: at least one of Ba, Sr and Ca, 0
≦ X <0.3), and Fe ₂ O ₃ , C
A piezoelectric ceramic composition characterized by containing at least one kind of r ₂ O ₃ , MnO ₂ , NiO, and Co ₂ O _{3 in} a total amount of 2.0 wt% or less.

[0007]

Embodiments of the present invention will be described below.

[0008] As a main component material, high purity BaCO
₃, SrCO₃, CaCO₃, Bi ₂O₃, TiO₂,
Nb₂O₅Was used. As an additive material, Fe
₂O₃, Cr₂O₃, MnO₂, NiO, Co₂O₃To
Using.

These are represented by the general formula A _{2 + 5X} Bi
_4-5X (Ti _1-X Nb _X ) ₅ O ₁₈ (A: Ba, S
r, Ca) was stoichiometrically mixed with the mixture and mixed by a ball mill for 20 hours. This was held at 800 ° C. for 1 hour and calcined, and then pulverized for 10 hours. Granulation using polyvinyl alcohol as a binder, pressure 1 ton /
It was pressed into a disk having a diameter of 20 mm and a thickness of 1 mm in cm ² . The firing was performed at a temperature of 1050 to 1150 ° C for 2 hours.

Thereafter, silver electrodes were provided on both sides of the obtained sintered body, and a DC voltage of 4 kV was applied in silicone oil at 100 ° C.
/ Mm was applied between the electrodes to polarize in the thickness direction.

[0011] Then, for these samples,
The electrical characteristics were evaluated. Piezoelectric characteristics are LF impedance
Electrical machine using resonance-anti-resonance method
The coupling coefficients kp and kt and the mechanical quality coefficient Qm are calculated and evaluated.
Valued. The dielectric properties are measured using an LCR meter.
The measurement is performed at a frequency of 1 MHz, and the relative dielectric constant ε₃₃ ^t/ Ε ₀
Was evaluated.

As an example, Table 1 shows that A = Ba and X = 0.
Ba _2.5 Bi _3.5 (Ti _0.9 Nb _0.1 ) ₅ O
₁₈ , additives (Fe ₂ O ₃ , Cr ₂ O ₃ , MnO
_2, NiO, electromechanical coupling coefficient kp when adding _Co 2 _{O 3),} kt, the mechanical quality factor Qm and specific dielectric constant ε
₃₃ ^t / ε ₀ is shown.

[0013]

[Table 1]

In Table 1, when Fe ₂ O ₃ is added,
Up to the addition amount of 2 wt%, the mechanical quality factor Qm is clearly improved as compared with the case without the additive. 2.5wt%
Even in the case of addition, the mechanical quality factor Qm is large, but the electromechanical coupling factors kp and kt are extremely small, and are not suitable for practical use. Similar results are obtained with other additives, with the additive being limited to 2 wt%. In addition, when not only one kind but also several kinds are added, an improvement in the mechanical quality factor Qm is observed. If the total amount exceeds 2 wt%, the electromechanical coupling coefficients kp and kt decrease, so that the total amount of 2 wt% is considered to be the limit.

A _{2 + 5X} Bi _4-5X (Ti _1-X
Nb _X ) ₅ O ₁₈ , in the range of 0 ≦ X <0.3,
Even when A was Sr or Ca alone or a mixture of Ba, Sr and Ca, the same effect of the additive as described above could be confirmed.

As described above, A _{2 + 5X} Bi _4-5X (Ti
_{1-X Nb X) 5 O} 18 (A: Ba, Sr, Ca, 0 ≦
X <0.3), wherein Fe ₂
By adding at least one of O ₃ , Cr ₂ O ₃ , MnO ₂ , NiO, and Co ₂ O _{3 in} a total amount of 2.0 wt% or less, the electromechanical coupling coefficient and the mechanical quality coefficient are high, and filters, vibrators, etc. Application to the application becomes possible.

[0017]

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

Claims (1)

[Claims] 1. A general formula A _{2 + 5X} Bi _4-5X (Ti
_{1-X Nb X) 5 O} 1 8 (A: Ba, Sr, at least one of Ca, represented by _{0 ≦ X <0.3), Fe} 2 O 3 as an _additive, Cr ₂ O _3, MnO ₂ , NiO, Co
A piezoelectric ceramic composition comprising at least one kind of ₂ O _{3 in} a total amount of 2.0 wt% or less.