JPH10279350A - High strength piezoelectric ceramic and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an piezoelectric ceramic, which is free from the large degradation of piezoelectric property such as electromechanical coupling factor and has high strength characteristic, and the producing method. SOLUTION: A sintered compact containing a piezoelectric ceramic crystal particle having <=3 μm average particle diameter and a metal oxide having <=1 μm average particle diameter as a dispersed crystal particle and having >=95% relative density to theoretical density is obtained by adding 0.01-5 vol.% at least one kind of a metal oxide powder selected form Al2 O3 , MgO, ZrO2 , HfO2 , Y2 O3 and TiO2 having <=1 μm average particle diameter to a piezoelectric ceramic powder having <=3 μm average particle diameter and after molding, irradiating the molding with micro wave and sintering at 900-1,300 deg.C by heating.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic and a method of manufacturing the same, for example, a ceramic filter, a ceramic resonator, an ultrasonic transducer, a piezoelectric buzzer, a piezoelectric ignition unit, an ultrasonic motor, a piezoelectric fan,
The present invention relates to a high-strength piezoelectric ceramic suitable for a piezoelectric actuator, a piezoelectric sensor such as an acceleration sensor, a knocking sensor, and an AE sensor, and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, piezoelectric ceramics have been used for various electronic components such as ceramic filters, ceramic resonators, ultrasonic transducers, piezoelectric buzzers, piezoelectric ignition units, ultrasonic motors, piezoelectric fans, and piezoelectric actuators. .

As a piezoelectric material used in these products, a piezoelectric ceramic composition containing PbZrO ₃ -PbTiO ₃ as a main component is used. Further, Nb ₂ O ₅ or MnO ₃ is used for the above main component. Metal oxides such as ₂ , Pb
(Nb _2/3 Mg _1/3 ) O ₃ and Pb (Nb _2/3 Co _1/3 )
By adding or substituting a composite perovskite oxide such as O _{3, the} piezoelectric characteristics are improved. These piezoelectric ceramics are required not only to have electrical characteristics such as piezoelectric characteristics and displacement characteristics, but also to have excellent durability and reliability with respect to porcelain itself with the recent progress of piezoelectric actuators. Piezoelectric ceramics having particularly excellent mechanical properties are strongly demanded.

[0004] In response to such demands, from the viewpoint of reducing the particle size of the crystal particles constituting the porcelain, a method of using fine particles as a raw material powder, adding an additive,
Or, from the viewpoint of strengthening the grain boundaries, there has been proposed a porcelain composition which is reinforced by ZrO ₂ fibers or SiC particles or has a high strength empirically.

[0005]

However, if a fine powder is used as a raw material simply to reduce the particle size,
The handleability during manufacturing is poor, and there are problems in terms of raw material cost and mass productivity, and further, there are cases in which basic characteristics required for piezoelectric ceramics such as a dielectric constant and an electromechanical coupling coefficient are affected.

[0006] In addition, in the strengthening by the composite, the composite reacts with the piezoelectric material in many cases to degrade the piezoelectric characteristics. Therefore, in order to perform the firing at a low temperature, the sintering method is limited to the hot press method. In addition, since firing at a low temperature for a long time is required, there is a problem that the piezoelectric characteristics are deteriorated due to decomposition of PbO and the like. Controlling the piezoelectric composition is most appropriate in order not to degrade the piezoelectric characteristics in combination with other components, but the Young's modulus of the piezoelectric material itself is mostly 5
Since the pressure is about 0 to 150 GPa, there is a limit in increasing the strength using only the piezoelectric material.

Therefore, it has been very difficult to achieve both the piezoelectric properties of the dielectric constant and the electromechanical coupling coefficient and the high strength.

SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric ceramic having high strength characteristics without significant deterioration of piezoelectric characteristics such as an electromechanical coupling coefficient, and a method for manufacturing the same.

[0009]

Means for Solving the Problems The present inventors have repeatedly studied the selection of additive particles that do not degrade the piezoelectric characteristics and the firing method with respect to the above-mentioned problems. In dispersing the material, it was found that by irradiating microwaves and heating and sintering, it was possible to increase the strength of porcelain while suppressing the deterioration of piezoelectric characteristics by densifying it with a fine structure. This has led to the present invention.

That is, the high-strength piezoelectric ceramic of the present invention comprises piezoelectric ceramic crystal particles having an average particle size of ₃ μm or less, and Al ₂ O ₃ , MgO, Zr having an average particle size of 1 μm or less.
It contains dispersed crystal particles composed of at least one metal oxide selected from the group consisting of O ₂ , HfO ₂ , Y ₂ O ₃ and TiO ₂ , has a relative density with respect to the theoretical density of 95% or more, and has a bending resistance at room temperature. The strength is not less than 100 MPa. Further, as a method of manufacturing such a piezoelectric ceramic, a piezoelectric ceramic powder having an average particle size of 3 μm or less is used for Al ₂ O ₃ , MgO, ZrO ₂ , HfO ₂ , Y ₂ O having an average particle size of 1 μm or less.
_At least one metal oxide powder selected from the group consisting of ₃ and TiO ₂ is added, and after molding, the molded body is irradiated with microwaves and heated and sintered at 900 to 1300 ° C. . In addition, the said metal oxide is 0.01
It is desirable to add and contain at a rate of about 5% by volume.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The piezoelectric ceramic of the present invention is mainly composed of piezoelectric ceramic crystal grains, and further has Al ₂ O ₃ , MgO, ZrO as phases independent between the grains of the piezoelectric ceramic crystal grains. ₂ , HfO ₂ , Y ₂ O
₃ and dispersed crystal particles of at least one metal oxide selected from the group consisting of TiO ₂ .

The composition of the piezoelectric ceramic crystal particles is not particularly limited as long as it has piezoelectric characteristics. For example, the composition of the piezoelectric ceramic crystal particles is a perovskite oxide crystal represented by PbZrTiO _3. Are perovskite-type crystals containing Pb, Zr, Ti, Nb, Sb and Cr as metal elements, as disclosed in JP-B-48-21876, and others, as disclosed in
5574, JP-A-4-170364, JP-A-7-1
It is composed of various compositions such as 87776 and JP-A-8-175867. In particular, the electromechanical coupling coefficient (K
A piezoelectric composition applied to a component requiring strength, such as a piezoelectric actuator having a high p), is suitable.

According to the present invention, it is important that the piezoelectric ceramic crystal particles have an average particle size of 3 μm or less. If the particle size of the piezoelectric ceramic crystal particles is larger than 3 μm, the effect of improving strength cannot be obtained, and a high bending strength at room temperature of 100 MPa or more cannot be obtained. In particular, the average particle size is desirably 2 μm or less. Here, the average particle size refers to an average value of a diameter in terms of a circular shape calculated from an area of a crystal obtained by image analysis of an SEM photograph, for example.

The dispersed crystal particles have an average particle size of 1 μm.
It is important that the thickness is 0.5 μm or less. If the particle size of the dispersed crystal particles is smaller than 1 μm, the strengthening by the dispersed crystal particles becomes insufficient, and it becomes difficult to achieve a strength of 100 MPa or more.

Further, Al ₂ O ₃ ,
MgO, ZrO ₂ , HfO ₂ , Y ₂ O ₃ and TiO ₂
The reason why at least one kind of metal oxide selected from the group is selected is that these metal oxides have low reactivity to piezoelectric ceramic crystal particles and small deterioration of piezoelectric characteristics. Among them, MgO, ZrO ₂ , Y
₂ O ₃ is desirable.

The dispersed crystal particles are blended in an appropriate amount as long as they do not adversely affect the piezoelectric characteristics. In particular, in the sintered body, 0.01 to 5% by volume, particularly 0.01 to 2% by volume, and more preferably 0.01 to 1% by volume.
Desirably, it is contained at a volume percentage. If the content is less than 0.01% by volume, the effect of improving the strength cannot be expected. If the content exceeds 5% by volume, the strength is improved to some extent, but it may affect the piezoelectric properties.

The method for producing a piezoelectric ceramic according to the present invention is produced by the following method.

First, as the piezoelectric ceramic component, for example, PbO, ZrO ₂ , TiO ₂ , Nb ₂ O ₅ , Sb ₂
After the respective raw material powders of O ₅ and Cr ₂ O ₃ are prepared to have a composition exhibiting the piezoelectric characteristics, they are mixed with a ball mill or the like for 10 to 10 minutes.
The mixture is wet-mixed for 24 hours to prepare a mixed powder. Next, after drying the mixed powder, it is calcined at 800 to 1300 ° C. for 1 to 3 hours, and pulverized again by a ball mill or the like to produce a piezoelectric powder having a perovskite crystal structure. At this time,
The average particle size of the calcined powder after pulverization is 3 μm or less, particularly 2 μm.
Adjust the crushing time and the like so as to be as follows.

The piezoelectric powder obtained as described above is added to Al ₂ O ₃ , MgO, ZrO ₂ , HfO ₂ , Y ₂ O ₃ and TiO having an average particle size of 1 μm or less, particularly 0.5 μm or less. _At least one kind of metal oxide powder selected from the group ₂ is added, wet-mixed again with a ball mill or the like, and dried to obtain a mixed powder. It is important that the average particle size of the metal oxide particles added at this time is 1 μm or less, particularly 0.5 μm or less, in order to enhance the sinterability and the strength of the sintered body. Further, it is desirable that the metal oxide is blended at a ratio of 0.01 to 5% by volume based on the total amount.

At this time, an organic binder is added at the same time,
A granulated powder is prepared using a spray drier or the like. Then, a molded article having a desired shape is produced using the granulated powder by a known molding method, for example, press molding, cold isostatic pressing, molding, injection molding, extrusion molding, or the like. Of course, tape forming may be performed by a doctor blade method or the like without using a spray dryer.

Next, the molded body obtained as described above is irradiated with microwaves in an oxidizing atmosphere such as the air, heated to 900 ° C. to 1300 ° C., and sintered to obtain a sintered body. . As the microwave source in the firing method of the present invention, any of a magnetron of 2.45 GHz, a klystron of 2 to 6 GHz, and a gyrotron of 24 GHz or more may be used. . Of course, the firing furnace may be a large continuous furnace that also has a microwave oscillator.

In the firing, a molded body or a firing crucible containing the molded body is placed in a heat insulating material which has a low thermal conductivity and withstands a high temperature, and is fired. The temperature is directly measured by a thermocouple and an optical thermometer. As the heat insulating material, low-density alumina fiber, mullite, or the like is preferable.

As the sintering crucible, alumina, magnesia, and mullite which are excellent in microwave transmittance and have high strength are preferable. In particular, when decomposition of PbO becomes a problem, a large amount of the compact is stored in a crucible and fired.

In the firing method using microwave irradiation, the heating rate can be increased by the principle of internal heating by microwave irradiation, the temperature is lower by about 50 to 200 ° C. than the conventional firing, and the holding time is 5 to 30 minutes. Can be fired in a short time. For example,
The sintering can be completed at a heating rate of 50 ° C./min and a holding time of 10 minutes. For this reason, decomposition of PbO, that is, sintering of an excellent piezoelectric ceramic with less composition fluctuation is possible.

In the present invention, Al ₂ O ₃ , MgO, ZrO ₂ , HfO ₂ , Y ₂ O ₃ used as dispersed crystal particles are used.
The metal oxides of TiO ₂ and TiO ₂ reacted with the piezoelectric perovskite-type crystal oxide from a temperature of 1300 ° C. or more, and tended to greatly affect the piezoelectric properties. By doing
As a result of firing at a low temperature and in a short time, the metal oxide can be prevented from reacting with the piezoelectric ceramic crystal particles and can be present as dispersed crystal particles, and the strength can be effectively increased easily.

[0026]

EXAMPLES PbO, ZrO ₂ , TiO ₂ as raw material powders
_Was weighed so as to have a composition of Pb (Zr _0.53 Ti _0.47 ) O ₃ , wet-mixed with a ball mill using zirconia balls, dried, and calcined at 1000 ° C. for 3 hours. Smash. At this time, the pulverization time is 3
Time, 10 hours and 24 hours, and the average particle size of the pulverized material (measured by laser dispersion diffraction method) was 6 μm, 3 μm,
μm, and three types of raw material powders for piezoelectric having different particle diameters were obtained.

Thereafter, an organic binder is added to the pulverized material,
Various metal oxides having an average particle size of 0.1 to 2 μm shown in Tables 1 and 2 were added so as to have the contents shown in Tables 1 and 2, and were ground again by a ball mill for 1 hour. After granulating the pulverized product by spray drying, the granulated powder is dispersed in 1.5 ton / cm ²
Was press-formed into a disc having a size of 23 mm in diameter and 2 mm in thickness and a test piece of 4 × 3 × 40 mm for strength measurement.

Further, these compacts were placed in an alumina crucible, degreased at 820 ° C. for 2 hours in the air using an alumina fiber heat insulating material, and then subjected to a frequency of 28 GHz.
Using a gyrotron having a maximum output of 10 kW as an oscillation source, the inside was fired in the atmosphere at a temperature and time shown in Tables 1 and 2 using a stainless steel microwave heating device. The heating rate in microwave firing was kept constant at 50 ° C./min. For comparison, some samples were placed in a crucible made of MgO in an electric heater furnace and fired at a heating rate of 5 ° C./min under the conditions shown in Tables 1 and 2.

The obtained sample was measured for bulk density by the Archimedes method, and the relative density was calculated from the theoretical density ratio. In addition, the strength measurement was polished to a 3 x 4 x 32 mm shape,
According to JISR1601, the four-point bending strength of five samples was measured, and the average value was determined. The average particle size is mirror-finished,
It was determined by image analysis from a SEM photograph of the chemically etched sample.

Further, the disk sample is polished to a thickness of 0.5 m.
m was formed. Electrodes are formed by baking an Ag paste on both principal surfaces of the disc, and applying a DC voltage of 3 kV / mm in silicon oil at 80 ° C. for 30 minutes for polarization treatment, and then evaluating the electromechanical coupling coefficient Kp. did.
The electromechanical coupling coefficient Kp was determined from the values of the resonance frequency Fr and the antiresonance frequency Fa measured by an impedance analyzer according to a calculation formula of Kp = (2.53 × (Fa−Fr) / Fr) ^1/2 . These results are also shown in Tables 1 and 2.

[0031]

[Table 1]

[0032]

[Table 2]

According to the results shown in Tables 1 and 2, samples Nos. 16 to 19 and 28 to 3 obtained by using the resistance heating method as the firing method were used.
In the case of 0, the average particle size of the piezoelectric ceramic crystal particles could not be suppressed to 3 μm or less under the condition that all of them could be densified, and as a result, the bending strength could not be increased to 100 MPa or more. On the other hand, even in a system containing no dispersed particles (Sample Nos. 3 and 20), the average particle size of the piezoelectric ceramic crystal particles can be suppressed to 3 μm or less by performing microwave firing. As a result, it was possible to achieve higher strength than when the conventional resistance heating method was used.

When the piezoelectric ceramic contains dispersed particles made of a metal oxide having an average particle diameter of 1 μm or less, the transverse rupture strength is greatly improved, and the piezoelectric characteristics are not greatly deteriorated. 0.01-5% by volume of particles
, A piezoelectric ceramic having a transverse rupture strength of 100 MPa or more could be produced.

However, even if microwave firing is used, the strength of the sample Nos. 1 and 2 in which the average particle size of the piezoelectric ceramic crystal particles is larger than 3 μm using powder of a raw material having a large average particle size is not improved. Only a few were seen.

Further, the average particle size of the dispersed particles is 1 μm.
In samples Nos. 34 and 37 exceeding m, the effect of improving the strength was not exhibited, and the piezoelectric characteristics were deteriorated.

[0037]

As described above in detail, according to the piezoelectric ceramic of the present invention, the fine dispersed crystal particles are dispersed by microwave firing without reacting with the piezoelectric ceramic crystal particles, whereby the piezoelectric characteristics are improved. It is possible to increase the strength of the piezoelectric ceramic without significantly affecting it. This makes it possible to use the piezoelectric ceramic under severe conditions, thereby expanding the field of use thereof and increasing the reliability as an electronic component.

Claims (4)

[Claims] 1. A piezoelectric ceramic crystal particle having an average particle size of ₃ μm or less, and Al ₂ O ₃ or Mg having an average particle size of 1 μm or less.
O, ZrO ₂ , HfO ₂ , Y ₂ O _3, and dispersed crystal particles composed of at least one metal oxide selected from the group consisting of TiO ₂ , wherein the relative density with respect to the theoretical density is 95% or more. High strength piezoelectric ceramics. 2. The high-strength piezoelectric ceramic according to claim 1, wherein said dispersed crystal particles are present at a ratio of 0.01 to 5% by volume. 3. An Al ₂ O ₃ , M having an average particle size of 1 μm or less for a piezoelectric ceramic powder having an average particle size of ₃ μm or less.
gO, ZrO ₂ , HfO ₂ , Y ₂ O _3, and at least one metal oxide powder selected from the group consisting of TiO ₂ are added, and after molding, the molded body is irradiated with microwaves,
A method for producing high-strength piezoelectric ceramics, wherein the method is heat-sintered at a temperature of from 00 to 1300 ° C. 4. The method according to claim 1, wherein said metal oxide powder is contained in an amount of 0.01 to 5% by volume.
The method for producing a high-strength piezoelectric ceramic according to claim 3, wherein the additive is added at a ratio of: