JPH10330164A - Piezoelectric substance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric substance capable of improving mechanical characteristics without largely reducing electric characteristics, by dispersing partially stabilized zirconia particles and/or stabilized zirconia particles in a specific ratio into a piezoelectric substance ceramic comprising lead titanate zirconate as a main component. SOLUTION: This piezoelectric substance has a structure comprising crystal particles composed of lead titanate zirconate as main crystal particles 1 and partially stabilized zirconia particles and/or stabilized zirconia crystal particles 2 existing at the grain boundary or in the grain of the main crystal particles 1. The partially stabilized zirconia particles and/or stabilized zirconia particles 2 are dispersed in an amount of 0.05-5 wt.% based on the total, are not subjected to solid solution in the main crystal particles or slightly to solid solution even if subjected to solid solution. Consequently the grain growth of particles comprising lead titanate zirconate as a main component is suppressed, the structure is made fine and the mechanical strength of a sintered compact can be improved.

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 excellent mechanical strength.

[0002]

2. Description of the Related Art Conventionally, products using piezoelectric ceramics include, for example, ceramic filters, ceramic resonators, ultrasonic transducers, piezoelectric buzzers, piezoelectric ignition units, ultrasonic motors, piezoelectric fans, piezoelectric sensors, and piezoelectric actuators. is there.

[0003] As piezoelectric ceramics used in these applications, lead zirconate titanate (PZT) has conventionally been used.
There is known a piezoelectric material mainly containing. This PZT ceramic has a large piezoelectric constant as compared with other piezoelectric materials, and is excellent in displacement performance.

[0004] Therefore, PZT-based piezoelectric materials have been widely applied to small displacement elements, ultrasonic vibration generating elements, and the like by utilizing their characteristics.

[0005] Conventionally, PZT sets the A site (Pb) to S
A method of substituting with r, Ca, or the like, or adding Nb, Ta, or the like to a B site (Zr, Ti) is known, and a composition combining them is disclosed (for example, Japanese Patent Application Laid-Open No. Sho 62-62).
298192).

For example, as piezoelectric ceramics for an actuator, mechanical properties (particularly strength) are important as well as electrical properties. A piezoelectric ceramic in which unstabilized zirconia particles are dispersed in PZT is known as a piezoelectric ceramic having improved mechanical strength (Felloele).
ctrics, vol129, p147).

This is because PZT powder having an average particle size of 0.5 to 1 mm is mixed with zirconia particles having an average particle size of 0.3 to 0.5 mm in a range of 1.3 to 13.2% by volume. It was added and baked under the conditions of 1250 ° C. × 2 hours. The zirconia particles are present at the grain boundary of PZT, whereby the grain growth is remarkably suppressed. When 8% by volume of the zirconia particles are dispersed, the mechanical strength is 100 MPa when no zirconia is added. 140MP for
It has improved to about a.

Further, a composite of zirconia fiber and PZT is also known (Journal of
the Ceramic Society of J
apan, vol. 102, P63 and P944).

This is because PZT calcined powder has a fiber length of 0.5
It is obtained by adding 0.5 to 9.5% by volume or 5 to 30% by volume of tetragonal or monoclinic zirconia fibers having a size of ３3 mm or 20 to 30 mm and firing at 1250 ° C. for 2 hours. The dispersed zirconia fiber has the shape of a fiber inside the PZT sintered body.
There is almost no effect on the grain growth of T, and the fracture toughness is improved by about 1.8 times.

[0010]

However, the method of improving mechanical strength by adding unstabilized zirconia particles involves a large number of microcracks due to martensitic transformation inside piezoelectric ceramics. In addition, there is a problem that the electrical characteristics are significantly reduced.

Therefore, when the amount of addition is increased, this effect becomes remarkable, and it has not been possible to improve the mechanical characteristics without lowering the electric characteristics.

When zirconia fibers are added to PZT, the fracture toughness is improved, but the grain growth of PZT cannot be suppressed at the time of firing, so that the mechanical strength cannot be improved.

An object of the present invention is to provide a piezoelectric body that can improve mechanical characteristics without significantly lowering electrical characteristics.

[0014]

According to the present invention, a piezoelectric material comprising lead zirconate titanate as a main component is provided with partially stabilized zirconia particles and / or zirconia particles at a ratio of 0.01 to 5% by weight based on the total amount. Alternatively, it is obtained by dispersing stabilized zirconia particles.

[0015]

The piezoelectric material of the present invention is composed of a piezoelectric material containing lead zirconate titanate as a main component, and a partially stabilized or stabilized zirconia, which undergoes a solid solution reaction with lead zirconate titanate during the sintering process. Since it does not occur and is localized at the grain boundary, the grain growth of crystal grains containing lead zirconate titanate as a main component is suppressed, and the structure is refined. Further, zirconia remains in the grain boundaries and in the grains of the sintered body (crystal grains mainly composed of lead zirconate titanate). With these, the mechanical characteristics of the piezoelectric body can be improved.

In addition, partially stabilized or stabilized zirconia differs from unstabilized zirconia in that 1
Since it does not show abnormal expansion due to martensitic transformation at around 100 ° C., it does not generate many microcracks that cause deterioration of electrical characteristics inside the sintered body mainly composed of lead zirconate titanate. The electrical characteristics are not significantly reduced even if the number of the elements is increased.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION A piezoelectric material of the present invention is contained in a piezoelectric ceramic containing lead zirconate titanate as a main component in a total amount of 0.05%.
-5% by weight of partially stabilized zirconia particles and / or
Alternatively, it is obtained by dispersing stabilized zirconia particles.

A piezoelectric ceramic mainly composed of lead zirconate titanate is, for example, Pb (Zr, Ti) O ₃ of Pb, Z
Some of r and Ti may be replaced by alkaline earth metals such as Ba, group 5a elements of the periodic table such as Nb, rare earth elements such as Y, group 6a elements of the periodic table such as Cr, and elements of the periodic table such as Co. It has been replaced with a Group 8 element or the like.

The crystal characteristics of the piezoelectric ceramic containing lead zirconate titanate as a main component have significantly reduced electrical characteristics when the average particle size is smaller than 1 μm, and deteriorated mechanical characteristics when the average particle size is larger than 3 μm. Therefore, it is desirable to have an average crystal grain size of 1 to 3 μm.

Partially stabilized zirconia (PSZ) and / or
Alternatively, stabilized zirconia (FSZ) may be any as long as it does not cause martensitic transformation within the firing temperature range. For example, zirconia containing a stabilizer composed of CaO and MgO of 16 mol% or more and zirconia containing a stabilizer composed of Y ₂ O ₃ of 8 mol% or more are generally stabilized zirconia, and CaO, MgO, Y _The case where the content of ₂ O ₃ is smaller than the above amount is the partially stabilized zirconia.

The content of partially stabilized zirconia and / or stabilized zirconia is desirably 0.05 to 5% by weight based on the total amount. This means that the content is 0.05
If the amount is less than 5% by weight, the effect of improving the mechanical strength is small. If the amount is more than 5% by weight, the mechanical strength is reduced and the electrical characteristics are significantly reduced. The content of partially stabilized zirconia and / or stabilized zirconia is desirably 0.05 to 0.5% by weight based on the total amount in order to improve mechanical strength and maintain high electrical characteristics. .

The partially stabilized zirconia and / or crystal particles of stabilized zirconia have an average particle diameter of 0.5 μm.
When the average particle diameter is smaller than m, the ratio of being incorporated into the crystal particles containing lead zirconate titanate as a main component increases, and the effect of suppressing the grain growth decreases. Because it drops significantly,
It is desirable to have an average crystal grain size of 0.5 to 1.0 μm.

As shown in FIG. 1, the piezoelectric body of the present invention has crystal grains mainly composed of lead zirconate titanate as main crystal grains 1, which are present in the grain boundaries and in the grains of the main crystal grains 1. This is a structure in which the crystal particles 2 of partially stabilized zirconia and / or stabilized zirconia are dispersed, and the partially stabilized zirconia and / or stabilized zirconia do not form a solid solution in the main crystal particles, or very little if any. It is.

Such a piezoelectric body is made of, for example, PbO, Z
The rO ₂ and TiO ₂ powders are mixed to a predetermined composition, calcined, and then pulverized so as to have an average particle size of 0.5 to 1.5 μm. To this, partially stabilized zirconia and / or stabilized zirconia powder having an average particle size of 0.5 to 1 μm is added in an amount of 0.05 to 5% by weight based on the total amount, and if necessary, a binder or a solvent is added and mixed. It is obtained by molding into a predetermined shape by molding, doctor blade method or the like, and firing in an oxygen-containing atmosphere such as in the air. The firing temperature is
In order to suppress the solid solution reaction of the material zirconia powder mainly composed of lead zirconate titanate, the lower the better, the better.
The firing temperature is about 100 to 1250 ° C., and the firing time may be 1 to 2 hours.

In the piezoelectric body of the present invention, the partially stabilized zirconia and / or the stabilized zirconia particles do not cause a solid solution reaction with the particles containing lead zirconate titanate as a main component, and are locally localized in the grain boundary or in the grains. , The grain growth of the particles containing lead zirconate titanate as a main component is suppressed to make the structure finer, whereby the mechanical strength of the sintered body can be improved.

Further, in the piezoelectric body of the present invention, since partially stabilized or stabilized zirconia is dispersed, abnormal volume expansion due to martensitic transformation does not occur even when heating to 1100 ° C. or more during firing. Therefore, even if the amount of zirconia is increased, the occurrence of microcracks is less likely to occur, and the electrical characteristics are less likely to decrease.

[0027]

EXAMPLE As a material mainly composed of lead zirconate titanate, Pb (Sb _1/2 Nb _1/2 ) having an average particle size of 0.8 μm was used.
_A calcined powder made of _0.05 (Zr _0.525 Ti _0.475 ) _0.95 O ₃ was used, and a zirconia powder (PSZ having a purity of 99% or more and an average particle size of 0.5 μm, stabilized with 3 mol% of Y ₂ O ₃ ) was used. ) Was added so as to be 0 to 7% by weight in the total amount. This mixture was mixed for 16 hours in a ball mill using ZrO ₂ balls, and then a binder was added and mixed. This mixed powder was press-molded under a pressure of 1 t / cm ² and fired in air at 1220 ° C. for 2 hours.

The obtained sintered body was 20 mm in diameter and 0.1 mm in thickness.
The plate was processed into a 5 mm disk, and silver electrodes were baked on the upper and lower sides of the disk. The disk on which the silver electrode was baked was polarized by applying an electric field of 3 kV / mm for 30 minutes in silicon oil set at 80 ° C., and then subjected to aging at 230 ° C. for 1 hour. Used, electrical characteristics, ie, electromechanical coupling coefficient Kr, relative permittivity ε ^T ₃₃
/ Ε ₀ was measured.

The bending strength of a sintered body obtained in the same manner as described above was processed into dimensions of 2 mm in width, 3.5 mm in length and 1.5 mm in thickness, and evaluated by a three-point bending test with a span of 2 mm.

Further, the average crystal grain size of the piezoelectric body was measured by an intercept method using an SEM photograph of a cross section of the sintered body. Table 1 shows the electrical characteristics, mechanical strength, and average crystal grain size of each sample produced by the above method. In addition, sample No. 5,
For 9 and 17, zirconia (FSZ) stabilized with 8 mol% of Y ₂ O ₃ was used. Sample No. 6, 10,
For zirconia unstabilized (purity 9
9% or more, average particle size 0.5 μm).

[0031]

[Table 1]

It can be seen from Table 1 that the inclusion of partially stabilized or stabilized zirconia can significantly reduce the crystal grain size of the sintered body and improve the mechanical strength.

On the other hand, when the content of zirconia is less than 0.05% by weight (samples Nos. 1, 2, and 3), the effect of addition is not recognized, and no improvement in bending strength is observed. When the addition amount exceeds 5% by weight, the crystal grains become small, but the bending strength is reduced, and the electromechanical coupling coefficient Kr is also significantly reduced (Sample Nos. 19 and 20).

Further, in the case of unstabilized zirconia (samples Nos. 6, 10, and 18), the electromechanical coupling coefficient Kr, It can be seen that the relative permittivity is extremely small.

[0035]

As described above, a partially stabilized or stabilized zirconia is dispersed in a piezoelectric ceramic mainly composed of lead zirconate titanate at a ratio of 0.05 to 5% by weight to obtain a mechanical device. A piezoelectric body having excellent mechanical strength can be obtained.
In addition, by using partially stabilized or stabilized zirconia, the occurrence of microcracks in the sintered body can be suppressed, so that the mechanical strength can be improved without lowering the electrical characteristics.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a piezoelectric body of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Main crystal particle 2 ... Partially stabilized zirconia and / or crystal particle of stabilized zirconia

Claims (1)

[Claims] 1. A method comprising dispersing partially stabilized zirconia particles and / or stabilized zirconia particles in a piezoelectric ceramic containing lead zirconate titanate at a ratio of 0.05 to 5% by weight based on the total amount. A piezoelectric body characterized by the following.