JP2524722B2 - Piezoelectric ceramic powder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a piezoelectric ceramic powder containing lead titanate particles as a main component.

<Prior Art> Lead titanate (PbTiO ₃ ) is widely used as a ferroelectric material having a perovskite structure in various piezoelectric materials and pyroelectric materials. In recent years, in particular, piezoelectric constant dh (=
d ₃₃ + 2d ₃₁ ) and gh (= dh / ε) are larger than other ferroelectric materials such as lead zirconate titanate (PZT),
It has become a focus of attention as a piezoelectric composite material for underwater acoustic exchangers such as transducers.

Here, the piezoelectric composite material refers to a material in which ferroelectric piezoelectric ceramic powder such as lead titanate or lead zirconate titanate is dispersed and mixed in a polymer material such as synthetic rubber or synthetic resin.

An object of the present invention is to provide a piezoelectric ceramic powder containing lead titanate as a main component, which has higher piezoelectric performance and which can be optimally applied as a dispersoid of a piezoelectric resin sheet corresponding to the above demand. It is what

<Means for Solving Problems> The present invention is a piezoelectric ceramic powder characterized in that 0.1 ≦ x ≦ 0.3 under the composition formula (1-x) PbTiO ₃ · xBiFeO ₃ .

<Operation> This piezoelectric ceramic powder has larger piezoelectric constants dh (= d ₃₃ + 2d ₃₁ ) and gh (= dh / ε) than the conventional lead titanate powder. Therefore, it is suitable as a piezoelectric composite material.

<Test Example> Commercially available PbO with a purity of 98.7% (average particle size of 3 μm or less), TiO _{2 with} a purity of 99.98%, Bi ₂ O _{3 with} a purity of 99.2%, and further 99.5% of purity.
Of Fe ₂ O ₃ of the composition formula (1-x) PbTiO ₃ · xBiFeO ₃
BiFeO ₃ was mixed in various mole fractions x, and PbO was added to promote the growth of crystal grains and self-disintegration.
Was prepared in an amount of 2.0 to 2.5% by weight excess. Then, this was dry-mixed for 3 hours with alumina boulders in a vibration mill. At this time, the inner wall of the pot of the vibrating mill was lined with urethane resin to prevent contamination of impurities. The ratio of powder: boulder = 2.5: 3.5 (Kg) was set.

Next, by applying pressure of 300 kg / cm ² using a mold, outer diameter 61 mm,
Make a tablet with a thickness of 10 mm, store it in a high-purity alumina crucible, and put it in an electric furnace at 1100 ℃, 1150 ℃ or 1250 ℃ for 2
Heat treatment by solid phase reaction was performed for ~ 4 hours. The heating and cooling rates at this time were 200 ° C. per hour. And
This sintered body was self-disintegrated by slow cooling.

Table 1 shows the relationship between the synthesis conditions (BiFeO ₃ mole fraction x, temperature) and the shape of the product.

A piezoelectric resin sheet was prepared by the following method using the powder formed in the above process.

First, the powder and the epoxy resin were weighed so as to be 50/50 vol% and stirred with a propeller stirrer for 10 to 15 minutes.

Then, it was preheated at 120 ° C. for 10 minutes in the dryer, which reduced the viscosity.

Then, it was poured into a mold, and the mold was set in a vulcanizing press and heated at 120 ° C. for 5 minutes without applying pressure for defoaming. Then, it was crosslinked at 120 ° C. and 37 tons to obtain a resin sheet having a predetermined shape. This was further dried at 80 ° C. for 12 hours, and then electrode layers were formed on the front and back surfaces thereof, which was polarized under the conditions of 100 KV / cm, 20 ° C. and 60 minutes, and this was used as a sample, and its characteristics were measured.

 The test results are shown in Table 2 and FIGS.

In this result, as shown in FIGS. 1 and 2, 0.1 ≦ x ≦
Within the range of 0.3, the piezoelectric constants dh (= d ₃₃ + 2d ₃₁ ) and g
The improvement of h (= dh / ε) was found to be maximum around x = 0.2.

Using dh × gh as an index of piezoelectric performance, a remarkable increase was confirmed in this range as shown in FIG. On the other hand, the
As shown in Figures 4 and 5, the dielectric constant and dielectric loss are
No big change was seen, and it turned out that there was no problem.

Furthermore, when using this piezoelectric resin sheet as an underwater hydrophone, in order to extract a good received signal, the noise S / N generated by the unreasonable stress acting in the plane direction as the ship moves It is desirable that the ratio is high. Therefore, it is desirable that the ratio between the piezoelectric constant d _{33 in the} thickness direction and the piezoelectric constant d _{31 in} the plane direction, and the absolute value of d ₃₃ / d ₃₁ are large. That is, it is expected that the piezoelectric constant has a large anisotropy. Then, when the absolute value of d ₃₃ / d ₃₁ showing anisotropy was plotted as shown in FIG. 8, a rise was observed, which was the maximum around x = 0.2. When x exceeds 0.3, the anisotropy is apparently further increased. As shown in FIGS. 6 and 7, the piezoelectric constants d ₃₃ and d ₃₁ decrease in inverse proportion to the increase from the value of x = 0.3, but the piezoelectric constant d ₃₁ decreases more than the decrease of the piezoelectric constant d ₃₃ . It is caused by a significant reduction and therefore does not indicate an improvement in properties.

In the region of 0.4 ≦ x ≦ 0.6, the coercive electric field is large, and
Dielectric breakdown easily occurs under the influence of Fe ions and it is difficult to polarize.

Therefore, it was confirmed that the above-mentioned composition powder is most suitable as the composite material for wave transmission and reception.

The piezoelectric ceramic powder of the present invention can be used by dispersing it in a polymer material such as rubber to form a sheet or a cable, and disposing electrodes on the upper and lower surfaces or the inner and outer surfaces thereof. Further, it is preferably used not only for an underwater acoustic transducer but also for displaying an image of a human body tube, a piezoelectric probe for investigating the state of a metal surface, a pyroelectric material for an infrared detection element, and the like.

<Effects of the Invention> As described above, the piezoelectric ceramic powder of the present invention has the piezoelectric constant dh
And has a large gh, and has an excellent effect that can be optimally used as a material for an underwater acoustic transducer or the like.

[Brief description of drawings]

1 is a graph showing the relationship between x and the piezoelectric constant dh, FIG. 2 is a graph showing the relationship between x and the piezoelectric constant gh, and FIG. 3 is a graph showing the relationship between x and the performance index dh × gh. 4 is a graph showing the relationship between x and the dielectric constant, FIG. 5 is a graph showing the relationship between x and the dielectric loss, FIG. 6 is a graph showing the relationship between x and the piezoelectric constant d ₃₃ , FIG. Is a graph showing the relationship between x and the piezoelectric constant d _31, and FIG. 8 is a graph showing the relationship between x and the anisotropy d ₃₃ / d ₃₁ .

Claims (1)

(57) [Claims] 1. A piezoelectric ceramic powder, wherein 0.1 ≦ x ≦ 0.3 based on the composition formula (1-x) PbTiO ₃ · xBiFeO ₃ .