JP3117247B2 - Method of manufacturing piezoelectric ceramic - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a piezoelectric ceramic used as an element for a piezoelectric buser, a receiver and a ceramic filter, and more particularly to an improvement of a method of manufacturing a piezoelectric ceramic having a small warpage due to firing.

[0002]

2. Description of the Related Art Piezoelectric ceramics have been widely used as materials for piezoelectric buzzers, receivers and filters.
Characteristics required for the piezoelectric materials used for these materials include a high relative dielectric constant and a high electromechanical coupling coefficient. As a material that can satisfy these required characteristics, a piezoelectric ceramic material containing PbZrTiO ₃ as a main component has been conventionally used. Specifically, Sn, Sb is used for PbZrTiO ₃ .
Alternatively, it is desired to further improve the characteristics by adding an oxide such as Nb or the like.
No. 4920.

[0003]

The above-described piezoelectric ceramics are:
All of them almost satisfy the characteristics required for piezoelectric ceramics, but when actually manufacturing products using these piezoelectric ceramics, most of the ceramics have a flat plate shape, Since appropriate dimensional accuracy is required, it is particularly required that porcelain does not warp due to firing. The occurrence of the warp has a bad effect on various piezoelectric products, which causes deterioration in quality and yield in an element processing step and variation in piezoelectric characteristics.

As described above, various improvements in composition have been proposed for piezoelectric ceramics as described above, but at present, the above-mentioned problems in concrete commercialization have not been studied in detail. .

In the field of ceramics, as a countermeasure for preventing warpage of the final sintered body, usually, the composition of the raw material, the particle size of the raw material, and the firing conditions are changed. No studies have been made, and there has been a problem that, depending on the preventive measures so far, adverse effects are exerted on the contrary and the piezoelectric characteristics are degraded.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for obtaining a piezoelectric ceramic having good dimensional accuracy by suppressing the occurrence of warpage of porcelain by firing without affecting the piezoelectric characteristics.

[0007]

[Means for Solving the Problems] The present inventors have investigated in detail the causes of warpage during firing, and found that the characteristics are greatly affected by the specific surface area of the calcined powder, and that the piezoelectric characteristics also fluctuate. From this, it was found that the above object was achieved by controlling the specific surface area to a specific range, and the present invention was achieved.

That is, the method for manufacturing a piezoelectric ceramic according to the present invention comprises:
After weighing and mixing metal oxide raw material powder constituting a piezoelectric ceramic of a system containing bZrTiO ₃ as a main component and adding oxides of Sn, Sb and Nb, the mixed powder is calcined. When pulverized, the pulverized product is pulverized so that its BET specific surface area is 2 to 8 m ² / g.
It is characterized by firing.

Hereinafter, the production method of the present invention will be specifically described. First, oxide powder of each metal constituting the piezoelectric ceramic, specifically, PbO, TiO ₂ , ZrO ₂ is used as a raw material powder.
, Etc. and weigh and mix thoroughly. The raw material used is not particularly limited, but the raw material preferably has an average particle size of 2 μm or less.

Next, the mixed powder is calcined. This calcination treatment is performed for the purpose of synthesizing a perovskite-type composite oxide, and the calcination conditions are slightly different depending on the composition, but are approximately 900 to 11 in an oxidizing atmosphere such as air.
This is performed at a temperature of 00 ° C. for about 1 to 6 hours.

The calcined product obtained in the calcining step is
Although the powders are agglomerated, they are pulverized using a pulverizing means such as a ball mill. According to the present invention, the BET specific surface area of the calcined powder finally obtained during the pulverization treatment is 2 to 2.
8m ² / g, be done by setting the conditions so particularly in 4~7m ² / g is important. Thereby, occurrence of warpage of the sintered body during firing can be reduced. The specific surface area may be controlled, for example, by selecting the diameter of the media of the ball mill, or controlling the number of revolutions and the grinding time.

Next, the calcined powder having the specific surface area controlled in the above range is formed into a desired shape by a known molding method, for example, press molding, sheet molding using a doctor blade or the like, injection molding, or the like.

The sintering is performed in an oxidizing atmosphere such as the air.
This is performed at a temperature of 0 to 1350 ° C. for about 2 to 6 hours. According to this firing, it is preferable in terms of piezoelectric characteristics that the sintered body be a high-density body having a relative density of 95% or more.

According to the present invention, the composition of the piezoelectric ceramic to which the above-mentioned manufacturing method can be applied is not particularly limited as long as it has PbZrTiO ₃ as a main component. As proposed in Japanese Patent Application No. 1-170600, one obtained by replacing the B site with Sn, Sb, and Nb is preferably used.

[0015]

1 and 2 show the relationship between the BET specific surface area of the calcined powder, the warpage of the final sintered body and the electromechanical coupling coefficient Kp.

According to FIGS. 1 and 2, as the specific surface area increases, the warpage of the sintered body tends to gradually increase. On the other hand, the Kp value sharply increases around ² to 4 m ² / g, and the value tends to be gradually stabilized.

The specific surface area of the calcined powder is also related to the sinterability, and the sinterability tends to increase as the specific surface area increases.

The present invention summarizes these various factors,
A major feature is that the BET specific surface area of the calcined powder is controlled to be ² to 8 m ² / g. That is, if the BET specific surface area is smaller than 2 m ² / g, it is difficult to obtain a dense porcelain though the warpage of the sintered body is small, the relative density is reduced, the piezoelectric properties are reduced, and if the BET specific surface area is larger than 8 m ² / g, Although the piezoelectric characteristics are improved, the warpage of the sintered body increases at the same time, which is not preferable.

[0019]

EXAMPLES Examples 1 to 7 Purity 99.0 as starting material
% Of commercially available Pb ₃ O ₄ , TiO ₂ , ZrO ₂ , Sn
Powders of O ₂ , Nb ₂ O ₅ , and Sb ₂ O ₃ were used. That is,
In order to form a piezoelectric ceramic containing PbZrTiO ₃ as a main component and adding Sn, Sb, and Nb oxides, the composition formula is xPbZ
rO ₃ + yPbTiO ₃ + zPb (Sn _1/3 Nb _{2d / 3} Sb
_{2 (1-d) / 3} ) When expressed as O ₃ , each value of x, y, z, and d is weighed so as to be as shown in Table 1, and wet-mixed with a ball mill.
It was dried and calcined at 900 ° C. for 3 hours.

The obtained calcined product is pulverized using a small-diameter zirconia ball (2 to 5 mmφ) as a medium using a ball mill or an attritor. At this time, the powder having a BET specific surface area in the range of about 1 to 10 m ² / g was obtained by changing the pulverization time.

Thereafter, an organic binder was added, and thereafter, pressure-molded into a plate-like molded body having a size of 20 × 30 mm and a thickness of 1.5 mm. This is placed in an oxidizing atmosphere at 1150-134.
Baking at 0 ° C. for 3 hours.

Next, 20 sintered bodies were taken out, the warpage a of the plate-shaped sintered body 1 was measured by the method shown in FIG. 3, and then silver electrodes were baked on both end surfaces of the polished one having a thickness of 1 mm. Was.

It was immersed in insulating oil at 80 ° C. and subjected to a polarization treatment by applying a DC voltage of 3 KV / mm between both electrodes.
Thereafter, the device was processed into a 5 × 5 mm, 1 mm thick element, and after 48 hours or more after polarization and 24 hours or more after element processing, a mechanical quality factor (Qm) and an electromechanical coupling factor (Kp) were obtained as piezoelectric characteristics by an impedance analyzer. ) Was measured.

The results are shown in Table 1. FIG. 1 shows the relationship between the specific surface areas of the calcined powders of Examples 1 to 3 and the warpage of the sintered body and the electromechanical coupling coefficient Kp. FIG. 2 shows the relationship between the curve, the warp, and the Kp value.

[0025]

[Table 1]

[0026]

[Table 2]

According to Tables 1 and 2, FIGS. 1 and 2, as the specific surface area of the calcined powder increases, the piezoelectric characteristics (Kp value) increase.
Tends to be good, but at the same time, the warpage of the sintered body tends to increase. By setting the specific surface area of the calcined powder to 2 m ² / g or more, the warpage is small and the porcelain excellent in piezoelectric characteristics is obtained. Can be obtained.

Further, according to the above-described embodiment, the change in the resonance frequency fr of the element after the temperature cycle test (-55 ° C. to 85 ° C., holding for 30 minutes, 20 cycles) is ± 0.3% or less, and the influence is observed. Did not. In the table of the present embodiment, Examples 1 to 3 are piezoelectric materials suitable for ceramic filters due to their characteristics, and Examples 4 to 7 are piezoelectric materials suitable for piezoelectric buzzers and receivers.

[0029]

As described above in detail, according to the method for manufacturing the piezoelectric ceramic of the present invention, the specific surface area of the calcined powder is limited to a specific range, so that the final firing can be performed without adversely affecting the piezoelectric characteristics. Warpage of the united body can be reduced. Therefore, it is possible to improve the production stability and reliability of the product and to reduce the production cost.

[Brief description of the drawings]

FIG. 1 is a view showing the relationship between the BET specific surface area of calcined powder, the warpage of porcelain, and the electromechanical coupling coefficient in Examples 1 to 3.

FIG. 2 is a diagram showing the relationship between the BET specific surface area of the calcined powders in Examples 4 to 7, the warpage of porcelain, and the electromechanical coupling coefficient.

FIG. 3 is a diagram showing a method for measuring the warpage of porcelain.

Claims (1)

(57) [Claims] 1. The method according to claim 1, wherein PbZrTiO ₃ is a main component, and Sn,
Sb, forming a step of forming a metal oxide powder mixed powder was weighed mixture of constituting a was based piezoelectric porcelain adding an oxide of Nb, the said mixed powder calcined to calcined product, the BET specific surface area of the calcined product is pulverized treated to be calcined powder of 2 to 8 m ² / g, a step of forming the calcined powder, the molded body unfired state by using the calcined powder process and method of the piezoelectric ceramic obtained by including a step of firing the shaped body in an oxidizing atmosphere to form.