JP2000072539A - Piezoelectric material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric material having an easily improved mechanical strength without largely reducing the piezoelectric characteristic. SOLUTION: This piezoelectric material is obtained by dispersing 0.05-1.0 wt.% ZrO2 particles based on the whole amount in a piezoelectric ceramic obtained by using Bax(Ti1-yZry)O3 [0.964h(x)<=1.04; 0.01<=(y)<=0.10] as a main ingredient and containing 0.05-2.0 pts.wt. Cu expressed in terms of CuO based on 100 pts.wt. main ingredient. The average particle diameter of main crystal grains comprising a perovskite type complex oxide containing at least Ba, Ti, Zr and Cu is 2-7 μm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric body, and more particularly, to a piezoelectric body having high mechanical strength.

[0002]

2. Description of the Related Art An actuator using a piezoelectric material uses a strain and a force generated through a piezoelectric phenomenon as a mechanical driving source, and performs positioning in a precision machine tool, optical path length control of an optical device, a flow control valve, and the like. Applications to ultrasonic motors or brake devices for automobiles are being developed. As a piezoelectric material used for an actuator, lead zirconate titanate (PZT) has been most widely used because of its excellent piezoelectricity.

However, recently, when lead-based waste is exposed to acid rain or the like, lead is eluted and adversely affects the environment. Therefore, lead-based waste is used as a substitute for PZT containing lead at about 60% of its own weight. There is a need for a lead free piezoelectric material.

As a lead-free piezoelectric material, barium titanate (BaTiO ₃ ) -based porcelain may be used. For example, Japanese Patent Application Laid-Open Nos.
No. 29430 proposes to use BaTiO ₃ -based porcelain. BaTiO ₃ -based porcelain is characterized by high relative dielectric constant (ε _33T / ε ₀ ) and high electromechanical coupling coefficient (k ₃₃ ), and exhibits a large piezoelectric strain constant (d ₃₃ ) of about 300 pC / N. It can be used as a piezoelectric material for a lead-free actuator.

[0005]

However, BaT
The piezoelectric strain constant (d ₃₃ ) of the iO ₃ -based porcelain is as small as about す る と as compared with that of PZT, and in the multilayer piezoelectric actuator using displacement in the thickness direction, it is １ ／ compared with the PZT multilayer. There has been a problem that only a small displacement can be obtained.

On the other hand, in order to obtain the same level of displacement as that of a PZT laminate, for example, the thickness of a piezoelectric element made of a BaTiO ₃ ceramic is reduced to about １ ／, and the element per unit length is reduced. It is conceivable to increase the number of sheets up to twice. However, when the thickness of the piezoelectric element is reduced, there is a problem that the mechanical strength of the porcelain itself is reduced, and the reliability of the piezoelectric actuator is reduced.

Therefore, in order to reduce the thickness of the piezoelectric element, it is necessary to improve the mechanical strength of the porcelain itself.
It is generally known that when compared with the same composition material, the denser and smaller the particle size, the better the mechanical strength of the porcelain. For example, by reducing the firing temperature of the porcelain or shortening the firing time, it is possible to control the particle size of the porcelain small, but in this case, the densification of the porcelain does not proceed sufficiently, There is a problem that the piezoelectric characteristics are deteriorated.

In addition, the porosity of the porcelain is reduced by using a hot press method to make the porcelain denser, and at the same time, the particle diameter is controlled to be small by controlling the pressure, the sintering temperature and the sintering time. Although it is possible to improve the mechanical strength, the hot press method has a problem in that the productivity is poor and it is difficult to manufacture many piezoelectric ceramics at once at low cost.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a piezoelectric body which can easily improve mechanical strength while maintaining high piezoelectric characteristics.

[0010]

Means for Solving the Problems The piezoelectric body of the present invention comprises Ba
_{x (Ti 1-y Zr y} ) O 3 (0.96 ≦ x ≦ 1.04,
0.01 ≦ y ≦ 0.10) as the main component, and the main component 10
Cu is 0.05 to 2.0 in terms of CuO with respect to 0 parts by weight.
In a piezoelectric ceramic containing parts by weight, 0.05 to
ZrO ₂ particles are dispersed at a ratio of 1.0% by weight. Here, at least Ba, Ti, Zr and C
It is desirable that the average particle size of the main crystal particles composed of the perovskite-type composite oxide containing u is 2 to 7 μm.

Furthermore, the main component is Ba _x [Ti _1-y (Zr
_1-a Sn _a ) _y ] O ₃ (0.96 ≦ x ≦ 1.04, 0.
01 ≦ y ≦ 0.10, 0.05 ≦ a ≦ 0.75).

[0012]

[Action] The piezoelectric material of the present _{invention, Ba x (Ti 1-y} Zr y)
O ₃ (0.96 ≦ x ≦ 1.04, 0.01 ≦ y ≦ 0.1
0) as a main component, and 100 parts by weight of the main component, Cu
Is contained in a piezoelectric ceramic containing 0.05 to 2.0 parts by weight in terms of CuO in an amount of 0.05 to 1.0% by weight of the total amount.
and rO ₂ the particles are those obtained by dispersing, ZrO ₂ particles in the sintering process, at least Ba, Ti, solid solution reacts with primary crystal particles made of perovskite-type composite oxide containing Zr and Cu occurs Hardly, mainly localized at the grain boundary, suppressing grain growth of the main crystal grains, reducing the grain size of the main crystal grains, improving the strength, and 0.05 to 1.0 weight in the total amount %, The ZrO ₂ particles are dispersed, so that the sinterability of the piezoelectric body is not deteriorated and the piezoelectric characteristics can be kept high. Furthermore, the main component 100
Cu is 0.05 to 2.0 in terms of CuO with respect to parts by weight.
By containing by weight, the piezoelectric properties of the piezoelectric body can be improved and the firing temperature can be lowered.

Further, the mechanical strength and the piezoelectric characteristics are further improved by setting the average particle size of the main crystal particles composed of the perovskite-type composite oxide containing at least Ba, Ti, Zr and Cu to 2 to 7 μm. Can be.

Further, S is based on 1 mol of Zr as the main component.
By substituting n at a ratio of 0.05 to 0.75 mol, it is possible to improve the piezoelectric characteristics on the low temperature side around -30 to 0 ° C.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The piezoelectric body of the present invention is made of Ba _x (Ti
_{1-y Zr y) O 3} (0.96 ≦ x ≦ 1.04,0.01
≦ y ≦ 0.10) as a main component, and 0.05 to 2.0 parts by weight of Cu in terms of CuO with respect to 100 parts by weight of the main component. ZrO ₂ particles are dispersed at a ratio of 1.0% by weight.

Here, x in the general formula representing the main component is set to 0.
The reason for setting 96 ≦ x ≦ 1.04 is that when x is larger than 1.04, the sinterability of the porcelain deteriorates, and the piezoelectric characteristics deteriorate. On the other hand, when x is smaller than 0.96, a reduction reaction easily occurs, and the piezoelectric characteristics of the porcelain are significantly reduced. x preferably satisfies the range of 0.98 ≦ x ≦ 1.02 from the viewpoint of excellent piezoelectric characteristics.

The reason why y is set to 0.01 ≦ y ≦ 0.10.
When y is smaller than 0.01, no improvement in piezoelectric properties due to the Zr substitution effect is observed, and when y is larger than 0.10, the Curie temperature (Tc) drops below 90 ° C. This is because heat resistance is reduced. y is preferably in the range of 0.05 ≦ y ≦ 0.07 from the viewpoint that the Curie temperature (Tc) is high and the heat resistance is excellent.

Further, in the present invention, Cu is contained in an amount of 0.05 to 2 parts by weight in terms of CuO with respect to 100 parts by weight of the main component. This is because the properties can be improved and the firing temperature can be reduced. That is, when Cu is less than 0.05 parts by weight in terms of CuO, the effect of improving the piezoelectric characteristics and the effect of lowering the firing temperature are small, and when it is more than 2 parts by weight, the piezoelectric characteristics deteriorate. From the viewpoint of improving the piezoelectric characteristics and lowering the firing temperature, it is desirable that Cu be contained in an amount of 0.1 to 1 part by weight in terms of CuO based on 100 parts by weight of the main component. Further, from the viewpoint of improving the piezoelectric characteristics of the porcelain, it is desirable that most of Cu be dissolved in the main crystal grains.

In the piezoelectric body of the present invention, 0.05 to 1.0% by weight of the total amount
In which ZrO ₂ particles are dispersed. here,
As the ZrO ₂ particles, monoclinic zirconia (m-ZrO 2
₂ ), partially stabilized zirconia (PSZ) and stabilized zirconia (FSZ) are used.

For example, zirconia containing at least 16 mol% of a stabilizer composed of CaO and MgO and zirconia containing at least 8 mol% of a stabilizer composed of Y ₂ O ₃ are generally stabilized zirconia. when the content of and the Y ₂ O ₃ is less than the weight of partially stabilized zirconia. Also, monoclinic zirconia (m-ZrO ₂ )
Is ZrO ₂ containing no stabilizer.

The ZrO ₂ particles are contained in an amount of 0.05 to
When the dispersion at a ratio of 1.0% by weight is less than 0.05% by weight, the effect of suppressing the grain growth of the main crystal particles is small, and the effect of improving the mechanical strength by miniaturizing the main crystal particles is small. From 1.0% by weight,
This is because the piezoelectric characteristics deteriorate. The ZrO ₂ particles are preferably dispersed at a ratio of 0.1 to 0.5% by weight based on the total amount in order to improve the piezoelectric characteristics and the mechanical strength.

When the ZrO ₂ particles are dispersed in a total amount of less than 0.5% by weight, monoclinic zirconia (m-ZrO ₂ ),
Either partially stabilized zirconia (PSZ) or stabilized zirconia (FSZ) may be used. However, when 0.5 to 1.0% by weight is dispersed, when monoclinic zirconia (m-ZrO ₂ ) is added, Since the rate of decrease in piezoelectric characteristics increases, partially stabilized zirconia (PSZ) and stabilized zirconia (FSZ) are desirable from the viewpoint of improving the piezoelectric characteristics.

[0023] Instead of ZrO ₂ particles, be dispersed Al ₂ O ₃ particles or MgO particles, substantially the same effect as dispersing ZrO ₂ particles. In addition, ZrO
_Two particles and Al ₂ O ₃ particles and / or MgO particles may be simultaneously dispersed.

In this case, the amount to be dispersed must be 0.05 to 1.0% by weight in the total amount.

The ZrO ₂ particles are added in a predetermined amount to the calcined powder of the main component. This effectively suppresses the growth of the main crystal particles during the sintering process, and reduces the average particle size of the main crystal particles. Can be reduced. ZrO in the porcelain
_{(2) The} particle size distribution of the dispersed particles is narrow because the particles are uniformly dispersed and the grain growth is effectively suppressed, and the surface of the dispersed particles is smooth because it does not hinder the densification of the porcelain during the sintering process. Desirably, the individual particles are nearly spherical.

The average particle size of these particles is 0.5 to
It is desirable to be in the range of 1.2 μm. This is because when the average particle size is smaller than 0.5 μm, the particles are easily taken into the main crystal particles, and the effect of reducing the particle size of the main crystal particles is reduced. On the other hand, when the average particle size is larger than 1.2 μm, the density of the porcelain is increased. This impairs the porcelain and lowers the piezoelectric characteristics of the porcelain.

Further, in the piezoelectric body of the present invention, when the average particle size of the main crystal particles is smaller than 2 μm, the piezoelectric characteristics are reduced. On the other hand, when the average particle size is larger than 7 μm, the effect of improving the mechanical strength is small. Is preferably in the range of 2 to 7 μm.

The average grain size of the main crystal grains is desirably 3 to 5 μm in view of the effect of improving the piezoelectric properties and the mechanical strength.

Further, the piezoelectric body of the present invention is formed of Ba _x [Ti
_1-y (Zr _1-a Sn _a ) _y ] O ₃ (0.96 ≦ x ≦ 1.
04, 0.01 ≦ y ≦ 0.10, 0.05 ≦ a ≦ 0.7
5) as a main component, and 100 parts by weight of the main component, Cu
Is contained in a piezoelectric ceramic containing 0.05 to 2.0 parts by weight in terms of CuO in an amount of 0.05 to 1.0% by weight of the total amount.
Desirably, rO ₂ particles are dispersed. That is, a part of Zr of the main crystal grain is substituted with 0.05 to 0.75 mol of Sn.

The reason why a part of Zr is replaced with Sn by a predetermined amount is to improve the piezoelectric characteristics on the low temperature side near -30 to 0 ° C. When the Sn substitution amount a is 0.05-0.
The reason for 75 is that if a is smaller than 0.05, the effect of improving the piezoelectric properties is small, and if a is larger than 0.75, the Curie temperature (Tc) decreases. In particular, from the viewpoint that the piezoelectric characteristics on the low temperature side are improved, the Sn substitution amount a is desirably 0.1 to 0.40.

The piezoelectric body of the present invention has at least Ba, T
ZrO ₂ particles are mainly present at the grain boundaries of the main crystal particles composed of perovskite-type composite oxides containing i, Zr and Cu, and are also partially present in the main crystal particles. . The ZrO ₂ particles in the porcelain do not or do not form a solid solution in the main crystal particles. Cu may partially exist in the grain boundary part of the main crystal grain.

Such a piezoelectric body can be obtained, for example, as follows. BaCO ₃ , TiO ₂ , ZrO
₂ , SnO ₂ , and CuO raw materials are weighed so as to have a predetermined composition, and the mixed powder is calcined so that the average particle size of the calcined powder is 0.7 to 1.2 μm. After pulverization, ZrO ₂ particles having an average particle size of 0.5 to 1.2 μm are added and mixed so as to be 0.05 to 1% by weight of the total amount.

If desired, a binder, a solvent, and the like are added to and mixed with the powder, formed into a predetermined shape by press molding, a doctor blade method, or the like, and then fired in an oxygen-containing atmosphere such as air to form a ceramic. Can be obtained.

The sintering temperature of this porcelain is preferably lower, and depends on the material composition, because the solid solution reaction of the main crystal particles and the ZrO ₂ particles to be dispersed is suppressed. And the firing time may be 2 to 5 hours.

In the piezoelectric body of the present invention, the ZrO ₂ particles do not cause a solid solution reaction with the main crystal particles and are locally dispersed mainly at the grain boundaries, so that the grain growth of the main crystal particles can be effectively performed in the sintering process. And the microstructure of the porcelain is refined. In addition, since the addition amount of these particles is specified, the mechanical strength of the porcelain can be easily improved without deteriorating the densification of the porcelain and maintaining a high piezoelectric characteristic. It is suitably used for applications.

[0036]

EXAMPLE 1 Each powder of BaCO ₃ , TiO ₂ , ZrO ₂ and CuO was
As shown in Table 1, they were weighed, mixed, and calcined. The calcined powder has a purity of 9 stabilized with 3 mol% of Y ₂ O _3.
9% or more, partially stabilized ZrO ₂ particles (PSZ) having an average particle diameter of 0.7 μm were added as shown in Table 1, and mixed with IPA as a solvent for 10 hours. Sample Nos. 6, 8, 1
0,12 as ZrO _2, purity of 99%, was used an average particle size 0.7μm monoclinic ZrO _2.

This mixed powder was press-formed into a column at a pressure of 1 t / cm ² and fired in air at the temperature shown in Table 1 for 2 hours to obtain a columnar porcelain having a diameter of 4 mm and a thickness of 6 mm.

Baking silver electrodes on the upper and lower surfaces of these cylinders,
The cylinder on which the silver electrode was baked was polarized in a silicon oil set at 80 ° C. by applying an electric field of 4 kV / mm for 30 minutes. Then, with an impedance analyzer,
Electrical characteristics (resonance-anti-resonance frequency, capacitance) were measured under room temperature (25 ° C.), the electromechanical coupling factor (k ₃₃₎
And the relative dielectric constant (ε _33T / ε ₀ ). Relative permittivity (ε
_33T / ε ₀ ) was plotted as a function of temperature to determine the Curie temperature (Tc).

The mechanical strength of the porcelain was evaluated by preparing a disc-shaped porcelain, processing it to a size of 2 mm in width, 3.5 mm in length, and 1.5 mm in thickness, and performing a three-point bending test with a span of 2 mm. did. Further, the average grain size of the main crystal grains of the porcelain was determined from the SEM photograph of the cross section of the sintered body by the intercept method.

The electromechanical coupling coefficient (k ₃₃ ), relative permittivity (ε _33T / ε ₀ ), mechanical strength (σ), average particle size (d) of porcelain, Curie temperature of each sample prepared by the above method (Tc) is shown in Table 1.

[0041]

[Table 1]

From Table 1, it can be seen that the piezoelectric body of the present invention
The mechanical coupling coefficient k ₃₃ at 50 ° C. is 50% or more, the relative dielectric constant (ε _33T / ε ₀ ) at 25 ° C. is 1900 or more, the mechanical strength (σ) is 120 MPa or more, and the Curie temperature (Tc) is 90.
It has a characteristic of not less than 1 ° C. and can be fired at 1300 ° C. or less.

In particular, in samples Nos. 8 to 11, 130 Mp
a of mechanical strength (.sigma.) of Sample No. 1
Mechanical strength (σ) of about 20 Mpa compared to Mpa
At the same time, a high electromechanical coupling coefficient (k ₃₃ ) of 60% or more and a high relative dielectric constant (ε _33T
/ Ε ₀ ).

On the other hand, when the amount of ZrO ₂ particles is 0.0
In the case of less than 5% by weight (sample Nos. 1, 2, 3),
It can be seen that the effect of the addition is not recognized and the improvement of the mechanical strength (σ) is not recognized. On the other hand, in Samples Nos. 16 and 17 in which the addition amount exceeds 1% by weight, the electromechanical coupling coefficient (k ₃₃ ) and the relative dielectric constant (ε _33T / ε ₀ ) are significantly reduced.

When x is 0.95 or 1.05 (Sample No.
18, 23), it can be seen that the electromechanical coupling coefficient (k ₃₃ ) and the relative permittivity (ε _33T / ε ₀ ) are significantly reduced.

Samples Nos. 24-29 show that the Curie temperature (Tc) decreases as y increases. Curie temperature (Tc) of sample No. 29 is 67 ° C.
It can be seen that it decreases to

From Samples Nos. 30 to 36, it can be seen that low-temperature sintering can be performed if the amount of Cu in terms of CuO is large, but the piezoelectric characteristics are deteriorated if the amount exceeds 2 parts by weight.

Sample No. 37 contained MgO and ZrO ₂ in a total amount of 0.25% by weight, and MgO and ZrO ₂ were added at a ratio of 0.5 mol each. Sample No. 38 contained 0.25% by weight of Al ₂ O ₃ , MgO and ZrO ₂ in total, and contained 0.25 mol, 0.25 mol of Al ₂ O ₃ , MgO and ZrO ₂ respectively. 0.5 mol was added. It can be seen that even in this case, it has excellent characteristics.

Example 2 In the same manner as in Example 1, the general formula Ba _x [Ti _1-y (Zr
_1-a Sn _a ) _y ] O ₃ , x = 1.00, y =
0.05, 0.20 parts by weight of CuO as an additive, 0.25% by weight of the partially stabilized ZrO ₂ particles described above,
The porcelain was produced in the same manner as in Example 1 above, while changing the value of a indicating the amount of Sn, and the same evaluation as above was performed. Also,
The electromechanical coupling coefficient (k ₃₃ ) and the relative dielectric constant (ε _33T / ε ₀ ) at −30 ° C. were determined and described together with the values determined at room temperature (25 ° C.). The results are shown in Table 2.

[0050]

[Table 2]

From the samples Nos. 39 to 46 in Table 2, Sn
As the substitution amount a increases, the electromechanical coupling coefficient (k ₃₃ ) at -30 ° C. and the relative dielectric constant (ε _33T / ε ₀ ) improve, and when a is 0.2, each of them takes a maximum value. I understand. On the other hand, when a is larger than 0.75, the Curie temperature (Tc) decreases.

[0052]

As described above, in the piezoelectric body of the present invention, Z
Since the rO ₂ particles do not easily undergo a solid solution reaction with BaTiO ₃ during the sintering process, the rO ₂ particles are mainly localized at the grain boundaries of the main crystal particles, suppressing the growth of the main crystal particles, and reducing the particle size of the main crystal particles. In addition, the strength can be improved, and the ZrO ₂ particles are dispersed at a ratio of 0.05 to 1.0% by weight of the total amount, so that the sinterability of the piezoelectric body is not deteriorated and the piezoelectric characteristics are maintained at a high level. In addition, by containing Cu, low-temperature sintering can be performed, and piezoelectric characteristics can be further improved.

Claims (3)

[Claims] 1. A _{Ba x (Ti 1-y Zr} y) O 3 (0.96
.Ltoreq.x.ltoreq.1.04, 0.01.ltoreq.y.ltoreq.0.10) and a piezoelectric material containing 0.05 to 2.0 parts by weight of Cu based on 100 parts by weight of Cu. during porcelain, piezoelectric, characterized in that by dispersing ZrO ₂ particles in a proportion of 0.05 to 1.0 wt% in the total amount. 2. The piezoelectric body according to claim 1, wherein the main crystal grains composed of a perovskite-type composite oxide containing at least Ba, Ti, Zr and Cu have an average particle size of 2 to 7 μm. 3. The method according to claim 1, wherein the main component is Ba _x [Ti _1-y (Zr _1-a Sn
_a ) _y ] O ₃ (0.96 ≦ x ≦ 1.04, 0.01 ≦ y
≤ 0.10, 0.05 ≤ a ≤ 0.75).