JPS6291458A - Manufacture of piezoelectric ceramics - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] (Technical field〕 This invention relates to a method for manufacturing piezoelectric ceramics.

[Background technology]

In recent years, electronic devices have become increasingly compact, and as a result, there is a strong demand for electronic components used in devices to be smaller and lighter. Piezoelectric ceramics are one of the materials for such electronic components. This piezoelectric ceramic is used in a wide variety of applications, including sensors, filters, piezoelectric vibrators, piezoelectric transformers, two-microphone pickups, piezoelectric bimorphs, piezoelectric unimorphs, and actuators.

One of the typical piezoelectric ceramics is lead zirconate titanate Pb(Zr, □TiX)03. Crystals of lead zirconate titanate (hereinafter referred to as "PZT") have a perovskite structure. Usually, this PZT
Multi-component piezoelectric ceramics containing other perovskite-structured materials are commercially available.

In order to make electronic components using piezoelectric ceramics smaller and lighter, it is necessary to improve the performance of piezoelectric ceramics. The spontaneous polarization of ceramics used in the above-mentioned commercially available piezoelectric ceramics is usually isotropic. Therefore, a high voltage is applied to this ceramic to perform polarization treatment (poling) to align the direction of spontaneous polarization in a specific direction (to provide anisotropy), thereby imparting piezoelectric function. However, since it is a ceramic, the residual polarization does not reach the polarization of a single crystal even if polarization treatment is performed. Leaving aside other characteristics, even if we focus only on this remanent polarization, the best time is 8
The limit is 2-83%. Moreover, even once polarization treatment is performed, depolarization is likely to occur. Therefore, over time, the piezoelectric properties deteriorate or become unstable under high stress conditions.

For this reason, although conventional piezoelectric ceramics have the advantage of having a high degree of freedom in element shape and low manufacturing costs, there has been a problem in that their use has not expanded dramatically.

[Purpose of the invention]

In view of the above-mentioned circumstances, it is an object of the present invention to provide a manufacturing method capable of obtaining high-performance piezoelectric ceramics suitable for reducing the size and weight of electronic components that utilize piezoelectric functions.

[Disclosure of the invention]

As a result of various studies in order to solve the above-mentioned problem, the inventors have found that the powder obtained is thin, such as flaky or needle-like, and has a crystalline state oriented in the thickness direction. , rapidly cooling the molten ceramic material,
By firing the ceramic material made from the powder produced in this way, the piezoelectric ceramics finally obtained will have high performance properties close to those of single crystals, and the advantages of ceramics will not be lost. He discovered this and completed this invention.

Therefore, the present invention provides a method for manufacturing piezoelectric ceramics that includes a step of pulverizing a ceramic material through a molten state into a powder for ceramic material.
The gist of this invention is a method for producing piezoelectric ceramics, which is characterized in that it is carried out so as to obtain a powder that is thin and has a crystalline state oriented in the thickness direction.

Hereinafter, an example of the method for manufacturing piezoelectric ceramics according to the present invention will be described in detail with reference to the drawings.

First, the preparation of oriented powder such as flakes will be explained.

P bo, T ioz, Z, which are ceramic materials
rO2 and trace amounts of other additives added as necessary are blended in such proportions that a desired composition of PZT is obtained. A fluxing agent is also added to the formulation to lower the melting temperature. Fluxing agents for the above formulations include NaCl-KCl system, PbOB
2Os system, KF PbFz Pbz (PO2)
2 series etc. are suitable. Addition of such fluxes significantly lowers the melting point of the formulation (approximately 1450°C), which varies depending on the type of fluxing agent and the amount added;
It will be about ℃. After grinding the blend with flux added,
The mixture is placed in a platinum crucible and heated at a temperature of about 900'C for about 2 hours to cause a reaction, thereby obtaining a pre-fired product.

After calcining, it is made into flaky powder using a device as shown in Figure 1. Place it in platinum crucible 1 and heat it to 1100~ with heater 2.
The temperature is raised to 1200° C. and heating is performed for about 2 to 3 minutes to obtain a melt 3. Air is pressurized through the alumina tube 4 provided at the top of the platinum crucible 1, and from the pore 1a at the bottom of the platinum crucible 1,
The melt 3 is dropped between the two cooling rollers 5, 5'. The dropped melt 3' is cooled very rapidly by contacting the surface of the roller 5.5', and falls as flaky powder 6,6. The temperature inside the melt 3' when it comes into contact with the rollers 5, 5' is as shown in FIG.
The surface that contacts both rollers is low, and the center is high. Therefore, a temperature gradient occurs in the left-right direction in FIG. 1, that is, in the thickness direction of the flaky powder 6. Therefore, in the case of PZT, the flaky powder 6 has an oriented crystalline state in which the C-axes of the crystals are aligned in the thickness direction. In the present invention, the term "ceramic material" refers to a material that is thin, such as this flaky powder, until it becomes a powder that has a crystalline state oriented in the thickness direction.

The powder created as described above usually contains a considerable amount of flux, so before molding,
This flux must be removed.

When the flux is NaCl-KCl, the flux is removed by ultrasonically cleaning the powder in hot water. The hot water is changed many times and the cleaning is repeated until no white precipitate of AgCl is detected in the hot cleaning water, for example by dropping an aqueous solution of A g N O3 into the hot cleaning water.

When the flux is PbO--B2oz, it is ultrasonically cleaned in an aqueous HCI solution (concentration 0.IN). Washing is repeated until there are no PB ions or B ions in the HCI aqueous solution. The degree of cleaning is measured by analyzing Pb ions and B ions using, for example, atomic absorption spectrometry.

If the flux is KF PbFz Pbz (PO4)z, the flux is separated by ultrasonic cleaning and physical pulverization, and then filtered.
The flux is removed by allowing it to fall into the filtered solution.

After removing the flux, a binder is added to the powder, and a green sheet is created using a doctor blade method or extrusion molding method.

In this case, the powder is flaky, so during molding,
The powders are not arranged in random directions, but are stacked one on top of the other in the thickness direction, so that even when viewed as a formed green sheet, the C-axes are aligned in the thickness direction. This green sheet (ceramic material) itself or a laminated green sheet (ceramic material) in which a plurality of green sheets are stacked and pressed to further increase the degree of orientation is fired. Green sheets originally have their C axes aligned in the thickness direction, so after firing (ceramic materials are sintered by this firing), they become ceramics with properties close to single crystals, making them extremely Has excellent piezoelectric properties.

As the flaky shape becomes progressively more elongated, it finally becomes needle-like.

Even if it is needle-shaped, the effect is no different from that of flake-shaped one. Therefore, in this invention, the thin shape refers to a flaky shape or a needle shape.

In the conventional manufacturing method, pbo evaporates during the firing process, so
The composition of the completed piezoelectric ceramic is not stable. If measures are taken to prevent evaporation of PbO during the firing process in order to stabilize the composition, the firing cost will increase. However, in the manufacturing method example according to the present invention described above, since a flux is added and melted, the ceramic material can be melted at a relatively low temperature, and the amount of PbO evaporated is extremely small. For this reason, not only the composition of the completed piezoelectric ceramic is stable, but also the special PbO
Since there is no need to take measures to prevent evaporation, manufacturing costs can also be reduced. In addition, there are other methods that can be used to obtain a crystalline state that has a thin shape such as a flaky shape or a needle shape, and is oriented in the thickness direction. Needless to say, it's a good thing.

Next, more specific examples and comparative examples will be shown.

(Example 1) As ceramic materials, P b O, Z r Oz,
and Ti0z. As fluxing agents, N a C] and K
A Na Cl -KCl system containing equal moles of Cl is used. P b (Z ro, s T to, s ) 03
Each ceramic material is blended so as to have the following composition, and a flux is blended with the same weight of bone as the total weight of the ceramic materials, and this blend is sufficiently pulverized and mixed using an agate mill. This pulverized and mixed compound was placed in a platinum crucible, covered with a lid, and heated to 1000°C in an electric furnace.
Heating was carried out for 2 hours at a temperature of 100 mL to cause a melting reaction. When this reaction product was analyzed by X-ray diffraction, it was found that the ceramic material was present in the flux as non-oriented square crystals. Next, the reaction product described above was placed in platinum crucible 1 of the apparatus shown in FIG.
After heating for a minute and melting, use the alumina vibrator 4.
Compressed air was introduced from the cooling roller 5.5' and dripped between the cooling rollers 5.5'. The obtained powder was in the form of flakes with a thickness of about 70 mm. The size varied between 5 and 200. Again, this flaky powder was analyzed by X-ray diffraction method)
It was confirmed that the C-axes were completely aligned in the direction of the grain, indicating an oriented crystalline state. To remove the flux, the powder is
It was placed in warm water at 0°C and subjected to ultrasonic cleaning. When washing was repeated 10 times, it was confirmed that no white precipitate was formed even when an aqueous silver nitrate solution was added to the hot water, and that chlorine was not eluted into the hot water. The size of the obtained powder is about 2 to 3 mm in diameter and 10 to 70 μm in thickness.
It was about m.

Next, this powder was formed into a green sheet. Prior to molding, for 100 parts by weight of powder, 8 parts by weight of polyvinyl butyral resin as a binder, 4 parts by weight of phthalate ester as a plasticizer, and 20 parts by weight of butanol as a solvent.
Parts by weight and 50 parts by weight of trichlorethylene were added, respectively, and mixed with a dispenser to form a slurry.

This slurry-like material was formed into a green sheet with a thickness of 200 mm using a doctor shaving method. This green sheet was cut into 30 m squares, and three square green sheets were stacked and press-molded to create a ceramic material. The pressure during pressing was 800 kg/cJ. In order to remove unnecessary organic substances from this ceramic material, it was heated in an air atmosphere at a temperature of 300° C. for about 7 hours. Next, in order to be able to perform atmosphere sintering of PbO,
The ceramic material was surrounded by dummy material having the same composition as the ceramic material to be sintered, placed in a magnesia crucible, and then fired after being covered with magnesia. Heating rate 200
The temperature was raised to 1260° C. at a rate of °C/hour, this state was maintained for 1 hour, and the temperature was lowered at a rate of 200°C/hour. Thereafter, an electric field of 3 kV/m was applied in silicone oil at 160° C. to perform polarization treatment to create piezoelectric ceramics.

(Example 2) PbO, 'ZrO, and TiO□ are used as ceramic materials. 50% by weight of pbo as a flux;
A PbO-B2O system containing 50% by weight of B2O3 is used. P
b (Z ro, s T io, s ) Each ceramic material is blended to have the composition of ○3, and a flux is added to the bone in an amount three times the total weight of the ceramic and rex materials, and this mixture is mixed into agate. Thoroughly grind and mix using a grinding machine. This pulverized and mixed compound was placed in a platinum crucible, covered with a lid, and placed in an electric furnace at a temperature of 1000°C for 2 hours.
Heating was carried out for a period of time to cause a melting reaction. When this reaction product was analyzed by X-ray diffraction, it was found that the ceramic material was present in the flux as non-oriented square crystals. Next, the above reactant was transferred to platinum crucible 1 of the apparatus shown in FIG.
After heating at 1200° C. for 5 minutes to melt, compressed air was introduced from the alumina pipe 4 and dropped between the cooling rollers 5 and 5'. The obtained powder is in the form of flakes with a thickness of about 7011 m and a size of 5.
I got angry between 20 and 20 degrees. Again, when this flaky powder was analyzed by X-ray diffraction, it was confirmed that the C-axes were completely aligned in the thickness direction, indicating that it was in an oriented crystalline state. In order to remove the flux, the powder was placed in HCI warm water (concentration IN) at about 60° C. and subjected to ultrasonic cleaning. After repeated washing 8 times, it was found that B ions were no longer excluded from the hot water. This was confirmed using atomic absorption spectrometry. The size of the obtained powder was 2 to 3 mm in diameter. Grade and thickness: about 10 to 70 I!m.

Thereafter, piezoelectric ceramics were produced in exactly the same manner as in Example 1.

(Example 3) PbO, ZrO□, Tfo2 as ceramic materials
use. As a flux, 40mol% of KF, PbF2
56mo1%, Pb3 (PO4)2 4mo1%
KF PbFz Pb, (POa)z with the composition
Use the system. Each ceramic material is blended in such a proportion that the composition becomes Pb (Zro, s Tfo, s 2 )03. The ceramic materials were added so that the total amount was 15 mol % and the flux was 85 mol %, and the mixture was thoroughly ground and mixed using an agate machine.

This pulverized and mixed compound was placed in a platinum crucible, covered with a lid, and heated in an electric furnace at a temperature of 1000'C for 2 hours.
Heating was carried out for a period of time to cause a melting reaction. When this reaction product was analyzed by X-ray diffraction, it was found that the ceramic material was present in the flux as non-oriented tetragonal crystals. Next, the above reactant was transferred to platinum crucible 1 of the apparatus shown in FIG.
After heating at a temperature of 1200° C. for 5 minutes to melt, compressed air was introduced from the alumina pipe 4 and dropped between the cooling rollers 5 and 5'. The obtained powder is flaky with a thickness of about 70 itm and a size of 5
It varied between 2011 and 2011. Again, when this flaky powder was analyzed by X-ray diffraction, it was confirmed that the C-axes were completely aligned in the thickness direction, indicating that it was in an oriented crystalline state. To remove the flux, the powder is placed in a glass beaker, warm water of approximately 60°C is added, and ultrasonic waves are applied to crush the powder to separate the flux, followed by washing. After repeated washing 25 times, no ions were released into the hot water, and the washing for removing the flux was completed. This confirmation was performed by atomic absorption spectrometry. The size of the obtained powder was approximately 2 to 3 W in diameter and 15 to 60 mm in thickness.

Thereafter, piezoelectric ceramics were produced in exactly the same manner as in Example 1.

(Comparative Example 1) The powder obtained in Example 1 after removing the fluxing agent was placed in a mortar, crushed into a fine powder, and passed through a sieve with a mesh size of 200 mesh. After that, piezoelectric ceramics were produced in the same manner as in Example 1 using the fine powder passed through the sieve.

Since it is a fine powder, it is not already in a crystalline state oriented in the thickness direction at the stage of forming a green sheet, but the orientation of the crystals is completely random.

The degree of orientation, electromechanical coupling coefficient, and dielectric constant of the piezoelectric ceramics of Examples 1, 2.3, and Comparative Example 1 were measured. The results are shown in Table 1 below. In the piezoelectric ceramics of Examples 1 and 2.3, it is clear that
Good orientation. As a result, 1. The electromechanical coupling coefficient that causes the transverse effect is 3. The value is very good. Regarding the relative dielectric constant, ε, −/ε. and ε2,7/ε. The difference between Examples 1 and 2.3 is extremely large, and it is confirmed that the orientation is much better than that of Comparative Example 1 from the viewpoint of electrical characteristics. Piezoelectric ceramics with excellent transverse effects are suitable materials for bimorph and unimorph devices.

The degree of orientation was measured as described above.

The degree of orientation of the ceramic material after firing was evaluated using an X-ray diffraction method before polarization treatment.

Targeting copper (Cu), using KoLI wire, C
The degree of orientation was calculated from the peak areas on the axis ((002) axis) and the a-axis ((200,] axis).

Using the X-ray peak of the sample obtained in Comparative Example 1, Po(
) obtained by the following formula. Po-([200)
Peak area on the axis) ÷ (Peak area on the (002) axis + Peak area on the (200) axis) Using the X-ray peaks of human samples obtained in each of Examples 1 and 2.3, calculate each Ps P, s = (, peak area on the (200,) axis) ÷ (peak area on the (002) axis + (200)
From Po and Ps obtained in this way, a numerical value Xt (=P o/
[Effects of the Invention] As detailed above, the piezoelectric ceramics manufactured by the manufacturing method according to the present invention are in a crystalline state with good orientation, so they are easy to polarize and are easy to depolarize. It has excellent piezoelectric properties that are close to those of single crystals, and the advantages of ceramics are not impaired at all. Therefore, it is possible to not only improve the performance of electronic components using piezoelectric ceramics but also to reduce their size and weight.

[Brief explanation of drawings]

FIG. 1 is a schematic explanatory diagram of an apparatus for creating flaky powder in an example of the piezoelectric ceramic manufacturing method according to the present invention;
FIG. 2 is a graph showing the internal temperature distribution state when powder is present between the cooling rollers of this device. 1... Platinum crucible 2... Heater 3... Melt 5.5'... Cooling roll 6... Flaky powder agent Patent attorney Takehiko Matsumoto '10 Figure 1 Waist 6 Figure 2 Enemies 1] Shogage Seifu Seisho (self-published in 1985) 7th stamp 60 scales IJti 230421 No. 2, name of invention Method for manufacturing piezoelectric ceramics 3, person making corrections 11 Relationship with cows Patent applicant Location: 1048 Kadoma, Kadoma City, Osaka Name (583) Matsushita Electric Works Co., Ltd. Representative: Representative Sadao Fujii 4, Agent Patent Application No. 60-230421 6, Specification subject to amendment 7, Amendment Contents (11 Correct the text r(200)J on page 18, line 15 of the specification to rcOO2)J. (2) Correct the text r(200)J on page 18, line 20 of the specification to r (002) J. (3) On page 19, line 4 of the specification, rPo /ps J is corrected to rPs/Pal.

Claims (8)

[Claims] (1) In a method for manufacturing piezoelectric ceramics that includes a pulverization step in which a ceramic material is molten and then turned into powder for ceramic materials, the pulverization is performed in a thin material and oriented in the thickness direction. 1. A method for producing piezoelectric ceramics, characterized in that the method is carried out to obtain powder having a crystalline state. (2) The method for producing piezoelectric ceramics according to claim 1, wherein the composition of the ceramic material contains PbO. (3) Powderization is achieved by dropping the molten ceramic material between two cooling rollers and bringing it into contact with the surface of the rollers to rapidly cool it. Manufacturing method of piezoelectric ceramics described. (4) The method for producing piezoelectric ceramics according to any one of claims 1 to 3, in which a flux is added to reduce the temperature when the piezoelectric ceramic becomes molten. (5) A method for producing piezoelectric ceramics according to claim 4, wherein the powder is formed into a ceramic material through a molding process, and the flux is removed before the molding process. (6) The method for producing piezoelectric ceramics according to claim 4 or 5, wherein the flux is NaCl-KCl based. (7) The method for producing piezoelectric ceramics according to claim 4 or 5, wherein the flux is PbO-B_2O_3-based. (8) Fluxing agent is KF-PbF_2-Pb_3 (PO_4)
A method for producing a piezoelectric ceramic according to claim 4 or 5, which is a _2 type piezoelectric ceramic.