JP3108724B2 - High durability piezoelectric composite ceramics and its manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic having excellent piezoelectric characteristics and high durability, and more particularly to a highly durable piezoelectric ceramic which is particularly excellent in repeated fatigue characteristics and is suitable for a piezoelectric actuator. And its manufacturing method.

[0002]

Heretofore, as a material used for the piezoelectric actuator, ceramic composition mainly composed of PbZrO ₃ -PbTiO ₃ are utilized, this Nb ₂
Metal oxides such as O ₅ and MnO ₂ , Pb (Nb _2/3 Mg
By adding or replacing a composite perovskite oxide such as _1/3 ) O ₃ or Pb (Nb _2/3 Co _1/3 ) O _{3, the} piezoelectric characteristics are improved. For example, Japanese Patent Publication No. 54-3
No. 6756 discloses that Pb (Nb _2/3 Sn _1/3 ) O ₃ −
PbZrO ₃ -PbTiO ₃ based piezoelectric ceramic composition is disclosed. These piezoelectric ceramics are required not only to have electrical characteristics such as piezoelectric characteristics and displacement characteristics, but also to be used in actuator applications. There is a strong demand for a highly durable piezoelectric actuator having particularly excellent characteristics. In response to such demands, as a method of improving fatigue resistance characteristics,
From the viewpoint of reducing the particle size of the sintered body and improving the mechanical strength, a method using fine powder as a raw material, ZrO ₂
Methods of adding additives such as fibers and SiC particles have been proposed (eg, Jpn. J. Appl. Phys. Vol. 34 (199)
5), pp 5276-5278).

However, the technique of simply reducing the particle size of the sintered body has a problem in that the basic characteristics required for the piezoelectric ceramic such as the dielectric constant and the electromechanical coupling coefficient are deteriorated. And above all, the improvement of the repetitive fatigue characteristics was small. In addition, ZrO ₂ fiber or Si
In the strengthening method by compounding C particles and the like, the mechanical strength is improved, but the sinterability is reduced. Therefore, the sintering method is limited to hot pressing. Is required, and degradation of piezoelectric characteristics due to decomposition of PbO becomes a problem. At the same time, the electromechanical coupling coefficient is significantly deteriorated. Furthermore, with regard to the above-mentioned compounding of the particles, small cracks and the like are generated in the ceramics due to the repetitive deformation induced by the electric field, and the piezoelectric characteristics are reduced, and in some cases, the mechanical reliability such as the porcelain is destroyed. There was a problem that was damaged. For this reason, it has been extremely difficult to achieve both the piezoelectric properties of the dielectric constant and the electromechanical coupling coefficient and the durability.

[0004]

Under these circumstances, the present inventors, in view of these results, focused on the fact that fatigue fracture occurs from the grain boundary, and as a result of intensive studies. In order to improve the repetitive fatigue characteristics induced by electric field, it is particularly effective to strengthen the grain boundaries of the piezoelectric ceramics, and the second phase is composed of a specific component different from the main phase composed of a perovskite-type crystal structure exhibiting piezoelectricity. The present inventors have found that the presence of the two phases in an appropriate amount easily strengthens the grain boundaries, and particularly improves the durability against fatigue, and has further studied to complete the present invention. That is, the present invention
An object of the present invention is to provide a piezoelectric composite ceramic having excellent high durability while maintaining high piezoelectric characteristics, and a method for manufacturing the same.

[0005]

The present invention for solving the above-mentioned problems comprises the following technical means. (1) an oxide ceramic having a perovskite type crystal structure exhibiting piezoelectricity with an average particle size of 1 to 8 μm as a main phase ;
0.1 to 5 fine particles of flat Hitoshitsubu径0.5μm or less of P t.
A highly durable piezoelectric composite ceramic containing 0 vol%, wherein the time until breakage or destruction is 100 hours or more due to repeated application of a high voltage sine wave of 1 kHz at 2 kV / mm in the polarization direction. Highly durable piezoelectric composite ceramics. (2) The highly durable piezoelectric composite ceramic according to (1), wherein 5% or more of the fracture surface due to the fracture or fracture is composed of an intragranular fracture surface. (3) (1) A method for producing a highly durable piezoelectric composite ceramic according flat <br/> Hitoshitsubu diameter 0.1～5.0Vol% is less P t 0.5 [mu] m powder Is mixed with a lead-based perovskite structure type piezoelectric ceramics mixed powder having an average particle diameter of 1 μm or less, granulated and molded in an oxidizing atmosphere.
A method for producing a highly durable piezoelectric composite ceramic, which comprises raising the temperature to 0 to 1300 ° C., holding for 0.5 to 4 hours, and sintering.

[0006]

Next, the present invention will be described in more detail. The piezoelectric ceramic of the present invention has an average particle size of 0.1.
Crystal consisting of Pt fine particles of 5 μm or less 0.1 to 5.0
It is composed of a perovskite oxide crystal having an average particle size of 1 to 8 μm, which is a piezoelectric particle represented by vol.% and PbZrO ₃ —PbTiO ₃ (PZT). At this time, it is important that intragranular fracture is seen in the fracture surface in an area ratio of 5% or more.
Area ratio indicating complete intergranular fracture or intragranular fracture is 5
%, High durability cannot be obtained. The fracture surface here refers to a fracture surface of a sample immediately destroyed by a bending test shown in JISR-1601 or a biaxial bending test using a disk.

The piezoelectric crystals constituting the piezoelectric ceramic of the present invention include Pb, Zr, Ti, and N as metal elements.
It is desirable to be made of a perovskite crystal containing b, Sb, and Cr. This is because the piezoelectric ceramics containing Pb, Zr, Ti, Nb, Sb, and Cr as metal elements have a high electromechanical coupling coefficient and have excellent piezoelectric characteristics. As these perovskite-type oxide crystals, specifically, for example,
_{Pb (Zr 0.5 Ti 0.5) O} 3, Pb 0.9 La 0. 1 (Z
r _0.5 Ti _0.5 ) O ₃ , Pb _0.94 Sr _0.06 (Zr _0.53 T
i _0.47 ) O ₃ , Pb (Mg _1/3 Nb _2/3 ) _0.375 Ti
_0.375 Zr _0.25 O ₃ is exemplified. It is also important that the average particle size of the main phase is 1 to 8 μm. When the average particle size of the main phase is smaller than 1 μm, the piezoelectric characteristics are low, and
If it is larger than this, the mechanical strength is low, so that the characteristics as a piezoelectric ceramic for an actuator are poor. The average particle size of the main phase is desirably 2 to 5 μm.

[0008] Next, as the second phase particles, Ru is constituted by fine particles <br/> of Pt. Further, in the ceramics, in addition to the main phase and the second phase, a phase in which the main phase and the second phase are dissolved may exist. It is important that the average particle size of the second phase is nano-sized particles of 0.5 μm or less, preferably 0.3 μm or less, and more preferably 0.1 μm or less. This is the second
If the particle size of the phase is larger than 0.5 μm, the piezoelectric characteristics are deteriorated, and the effect of improving the durability is small. The average particle size in this case refers to the average value of the diameter of the particles observed by SEM, TEM, or the like. The content of the second phase is 0.1
It is not less than vol% and not more than 5 vol%. This is 0.1v
If the content is lower than 5% by volume, the grain boundary strengthening that may cause intragranular fracture does not occur. Desirably, 0.1-1.0 vol%,
More preferably, 0.1-0.5 vol% is optimal.
The second phase has a crystal structure other than the perovskite structure, for example,
It has a corundum structure, a spinel structure and the like.

The method for producing a piezoelectric ceramic according to the present invention comprises:
For example, it is produced by the following method. First, for example, PbO, ZrO ₂ , TiO ₂ , Nb ₂ O
_5, Sb ₂ O _5, each raw material powder of Cr ₂ O ₃ were weighed prescribed amount, 10 to 24 hours using a ball mill and a wet mixed to prepare a mixed powder. After drying the mixed powder, 800-130
The mixture is calcined at 0 ° C for 1 to 3 hours and pulverized by a ball mill or the like. At this time, it is desirable from the viewpoint of sinterability that the average particle size of the calcined powder after grinding is small. Next, a predetermined amount of Pt-added particles having an average particle size of 0.5 μm or less were mixed with the obtained piezoelectric powder,
The mixture is wet-mixed again with a ball mill and dried to obtain a mixed powder. In this case, it is preferable to use a mixed powder having an average particle size of 1 μm or less. This is because, when a raw material larger than 1 μm is used, the sinterability becomes extremely poor, and the expected strength cannot be obtained. As a method for adding this time, even if added in powder or PtCl _4, it may be AgNO ₄ or a method in which the solution is reduced with the. The average particle size of the particles to be added may be 0.5 μm or less, more preferably,
0.1 μm or less is good from the viewpoint of sinterability and characteristics. At this time, if desired, an organic binder is added at the same time, and a granulated powder is prepared using a spray drier or the like. The granulated powder is formed into a desired shape using a known technique such as press molding, CIP molding, or injection molding. Of course, tape forming may be performed by a doctor blade method or the like without using a spray dryer. These compacts are placed at 800 ° C. to 1300 ° C. in the air or in an oxygen atmosphere.
And hold for 0.5 to 4 hours to obtain a sintered body by sintering. In this case, a ceramic having excellent piezoelectric properties cannot be obtained under these conditions. At this time, with respect to the holding temperature and the holding time, it is preferable to perform sintering at a temperature as low as possible for a short time in order to enhance the piezoelectric characteristics. When a Pb-containing piezoelectric powder is used, it is better to suppress the decomposition of PbO by arranging a compound having a higher vapor pressure of PbO, such as PbZrO ₃ .

[0010]

The present invention is described below with reference to Examples.
However, the present invention is not limited to the embodiment shown in FIG. Example 1) Preparation of sample PbO, ZrO as raw material powder_Two, TiO_TwoTo Pb (Z
r_0.52Ti_0.48) O_Three And weighed so that the composition of
O_Two Wet mixed with a ball mill using a ball and dried
Then, it is calcined at 1000 ° C. for 3 hours, and the calcined material is again boasted.
Pulverized for 24 hours using a laser mill.
The raw material powder for piezoelectrics having a particle diameter of 1 μm is obtained.
Was. Then, the additives shown in Tables 1 to 3 were added to the pulverized material in Table 1.
And added again at the addition rate shown in Table 3, and again 12 hours in a ball mill
Crushed. Preformed granulated powder and 0.5ton / cm^Two of
A circle consisting of 23 mm diameter and 2.5 mm thick under pressure
Press-formed into a plate and 2 ton / cm^TwoCI at pressure
P molding was performed.

These compacts are placed on a Pt sheet in a high-purity alumina crucible, and PbZr
An appropriate amount of O ₃ was placed. The firing conditions were firing in the air at the temperatures shown in Tables 1 to 3. The holding time is 2 hours and the heating rate is 5
° C / min.

2) Test Method The bulk density of the obtained sample was measured by the Archimedes method, and the relative density was calculated from the theoretical density ratio. Further, the sample was polished to form a disc having a thickness of 1.0 mm. Electrodes are formed by baking Ag paste on both principal surfaces of the disc, and a polarization process is performed by applying a DC voltage of 2 kv / mm in silicon oil at 120 ° C. for 30 minutes, and then evaluating the piezoelectric properties and durability. did. The durability was measured at 2 kV / mi while maintaining the polarized sample at 25 ° C. in silicone oil.
The test was performed by applying an AC voltage of n, 1 kHz.
An AC voltage was applied to each sample for 1 minute, 10 minutes, 1 hour, 10 hours, 50 hours, and 100 hours, and a strength measurement was performed by a biaxial bending test before and after the test. When (strength after voltage application test / strength before voltage application test) was 20% or less, it was determined to be broken.

As a piezoelectric characteristic, an electric coupling coefficient Kp was measured. Kp was determined from the values of the resonance frequency Fr and the antiresonance frequency Fa measured by an impedance analyzer according to the following formula. Kp = (2.53 × (Fa−Fr) / Fr) _1/2 Intra-granular fracture rate is obtained by observing the fracture surface of the strength test before voltage application by SEM, It was determined by an image analyzer. In addition, the crystal phase was identified by X-ray diffraction, and it was confirmed whether a crystal phase other than the tetragonal perovskite structure represented by 33-0784 was observed on a JCPDS card. The average particle size of the sintered body was calculated from the SEM photograph, and the average of the main phase was calculated by an intercept method using 300 to 400 particles. For the second phase particles, the average value of the minor axes of 10 particles was calculated.

3) Results These results are shown in Tables 1 to 3. In the table, Pt
Other than * and * indicate outside the product of the present invention. The t of the crystal phase is
Tetragonal PZT and UK indicate unknown crystal phases other than tetragonal PZT.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

According to Tables 1 to 3, Al ₂ O ₃ , MgO,
No. 3 without additives such as ZrO ₂ In Nos. 1 and 2, although the electromechanical coupling coefficient was high, it broke in only 1 minute after the endurance test. On the other hand, Al ₂ O ₃ , MgO, ZrO ₂ , AgO,
A sintered body produced by adding 0.1 to 5.0 vol% of Pt has excellent characteristics for an actuator having an electromechanical coupling coefficient of 50% or more, and has a strength retention ratio even after a 100-hour durability test. Was expensive. These sintered bodies are 5%
It shows a larger intragranular fracture rate and also has a tetragonal P
A second phase other than ZT was identified. Further, even after the durability test, no significant deterioration of the piezoelectric characteristics was observed. Also,
No. ₂ to which Nb ₂ O ₅ and MnO ₂ were added. In Nos. 12 to 13, the strength after the durability test was significantly reduced, and the intragranular fracture rate was less than 5%, resulting in insufficient durability.
Further, in the case of No. 3 in which the average particle size of the main phase exceeded 8 μm. In No. 14, the mechanical strength was low and the average particle size of the second phase was 0.5 μm or more. 15 and No. In Nos. 17 to 19, although Kp was low and high durability was observed, characteristics for actuator use could not be obtained. Note that the above N
o. Nos. 6 to 7 are examples and Nos. 1 to 5 and 8 to 19 show comparative examples.

[0019]

According to the present invention, 1) a piezoelectric ceramic having high durability can be provided while maintaining high piezoelectric characteristics. 2) Grain boundaries of the piezoelectric ceramic can be easily strengthened. ) Fatigue characteristics can be greatly improved, 4) Ceramics with little deterioration of electrical characteristics can be obtained, and 5) Highly durable piezoelectric ceramics suitable for piezoelectric actuators can be provided. The effect is achieved.

────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Huang Haijin 3-1-1, Meijo, Kita-ku, Nagoya-shi, Aichi Prefecture Meiji-jo Housing No.3 Building 108 (72) Inventor Mutsuo Shanto 5-41, Narukocho, Midori-ku, Nagoya-shi, Aichi Prefecture Address Examiner Yuichi Fukakusa (56) References JP-A-10-279350 (JP, A) Hae Jin Hwang, et al. "Effect of Secondary display on Mechanical and Piezoelectric Properties of the PZT-Based Nanocomposites, 1996. Field (Int. Cl. ⁷ , DB name) C04B 35/49 CA (STN) REGISTRY (STN)

Claims (3)

(57) [Claims] 1. A oxide ceramics containing the perovskite-type crystal structure exhibiting piezoelectricity of the average particle size 1~8μm the main phase, 0 microparticles flat Hitoshitsubu径0.5μm following P t.
A highly durable piezoelectric composite ceramic containing 1 to 5.0 vol% in which the time until breakage or breakage is 100 by repeatedly applying a high voltage sine wave of 1 kHz at 2 kV / mm in the polarization direction. Highly durable piezoelectric composite ceramics for at least a time. 2. The highly durable piezoelectric composite ceramic according to claim 1, wherein 5% or more of the fractured surface due to the fracture or fracture is composed of an intragranular fracture surface. 3. The method for producing a highly durable piezoelectric composite ceramic according to claim 1, wherein the method comprises 0.1 to 5.0 vol.
% Of an average particle size 1μm or less of the lead-based perovskite structure type piezoelectric ceramic powder mixture Rights Hitoshitsubu diameter powder late following Pt 0.5 [mu] m were added, granulating, molding, in an oxidizing atmosphere 800-1300 A method for producing a highly durable piezoelectric composite ceramic, wherein the temperature is raised to a temperature of 0 ° C., held for 0.5 to 4 hours, and sintered.