JPS6022513B2 - piezoelectric porcelain - Google Patents

Description

Detailed Description of the Invention The present invention provides an electromechanical transducer that has a large electromechanical coupling coefficient, a small dielectric constant, a large frequency constant, a small crystal grain size, and a uniform and fine porcelain structure, and which can be used at high frequencies. This invention relates to piezoelectric porcelain useful as a material.

Additionally, barium titanate-based porcelain and zircon/lead titanate-based porcelain are known as piezoelectric porcelain.

In particular, zircon-lead titanate-based porcelain has an electromechanical coupling coefficient (
It has a large dielectric constant (K) and a large dielectric constant (d), and is used in many fields as an electromechanical transducer. Recently, with the development of electronic circuits, there has been a strong demand for an electromechanical transducer that can be used in a high frequency range, particularly in a range of several megawatts or more.

Conventional barium titanate-based porcelain and zircon-lead titanate-based porcelain have large dielectric constants, so losses are large in such high-frequency applications. In addition, since the frequency constant is small, when it is put into practical use in such a high-frequency device, it is necessary to make the device very small in size, such as by making the thickness of the device extremely thin, and good results have not been obtained in practice. A solid solution based on NaNbo3-LiNbo3 has been found as a composition that solves these problems.

These compositions are characterized by a low yield factor and a large high frequency constant. However, with these compositions, it is difficult to obtain a fine and uniform porcelain structure. That is, since the temperature range suitable for crystallization is narrow, abnormal grain growth is likely to occur, resulting in large and non-uniform crystal grain sizes, and furthermore, many pores remain. By the way, in high frequency castles, the non-uniformity of these porcelain structures significantly reduces the performance as an electromechanical transducer, and the large crystal grain size also reduces the strength of the element, especially the small size required for such high frequencies. These problems pose a major obstacle in practical use.

Special manufacturing methods such as hot press sintering have been proposed as a way to solve these problems, but even then, the range of conditions such as sintering temperature is narrow and satisfactory results cannot be obtained. In addition, it complicates the manufacturing method, which is not preferred in practice.

The present invention eliminates the above-mentioned drawbacks of the conventional piezoelectric ceramics and provides a completely new piezoelectric ceramic that can be used as a high-frequency electromechanical transducer. That is, the present invention is based on the general formula (Na
,★,Lix)(NL-y,SQ)03[1], and the value of ×,y is 0.03<x<0.14,0.001<y
Piezoelectric porcelain with a composition in the range <0.03. The piezoelectric porcelain according to the present invention has the characteristics that a uniform fine porcelain structure with small crystal grain size can be obtained by a normal firing method, a large electromechanical coupling coefficient, a small dielectric constant, a large frequency constant, and high frequency resistance. In particular, it is a suitable material for practical use as an electromechanical transducer at the M position or higher. FIG. 1 shows the composition range of the piezoelectric ceramic according to the present invention.

x and y in the figure correspond to x and y in formula [1], and the numbers correspond to sample numbers in Table 1, which will be described later. Here, the piezoelectric porcelain of the present invention has a range surrounded by four points A, B, C, and D in the figure.
That is, 0.03<text<0.140.001<y<0.03
0.03, especially from the point of view of crystal grain size and dielectric constant.
<x<0.10, 0.002<yo. 01 is 0.1
When <×<0.14, 0.002 mm and 0.03 are desirable.

The reason for the composition limitation in the present invention is that when x<0.03, the applied voltage required for polarization treatment becomes extremely large, making it difficult to put it to practical use. On the other hand, if it is >0.14, a burnt striped body consisting of a single phase is not obtained, but a moat phase is obtained, and the predetermined piezostatic property is not exhibited. In addition, when y<0.001, crystal grains grow very easily during the solidification process, and the crystal grain size decreases to 1.
Since abnormal grain growth occurs beyond the zero peak, a uniform porcelain composition cannot be secured by the normal competitive bonding method. On the other hand y>0.03
In this case, a uniform porcelain structure cannot be obtained as in the case where y is 0.001. To produce the piezoelectric porcelain of the present invention, for example, Na
2CQ, Lj2C03, Nb203, Sb203 and other component raw materials are mixed in predetermined amounts and weighed, and the mixture is heated to 800~
1,000 times zero for 2 to 8 hours.

After pulverizing the calcined product, it is molded, and then the molded product is
1. Porcelain is obtained by crystallization at 300°C. This porcelain is polarized using a predetermined method to give it piezoelectric properties. Examples Starting raw material powders include Na2C03, Li2C03, NQ
03, Sb203 was used.

The purity of carbonate is 99.5% or more, and both NQ03 and S et al. 03 are 99.5% or more. A predetermined amount of these raw materials was weighed, wet mixed in a ball mill using ethanol, and then the mixture was dried. The obtained mixed powder was suspended in air at 850 to 90 psi for 4 hours. The obtained calcined product was pulverized and then pressure-molded into a disk with a thickness of 2 ribs and a diameter of 25 mm at a pressure of 500 to 600 k9/cm. This disk sample is 115 and 0 to 1
It was sintered in air at a temperature of 280°C. The high specific gravity and true specific gravity of the obtained porcelain were measured, and the crystal grain size was also measured by observing the porcelain structure. To observe the porcelain structure, first mirror-polish the circular surface of the obtained disc porcelain, and then polish this surface once.
．． Thermal etching was carried out by heating in the air at 0.050 qo for about 15 minutes, and the surface was observed under a microscope. Next, regarding the piezoelectric properties, the obtained disk porcelain was molded and polished into a disk with a thickness of 1 inch and a diameter of 18 mm, Ag electrodes were baked on both sides of this disk, and the disk was placed in silicone oil at 100 degrees Celsius. Polarization treatment was performed by applying a DC voltage between both electrodes for 30 minutes with a DC voltage on the thigh V/side.

After the polarized sample was left for 2 hours, the electromechanical coupling coefficient (Kp) and frequency constant (NP: resonant frequency x diameter) in radial vibration were measured in order to evaluate the piezoelectric properties.

Measurements were made at 1, R. E. Kp was calculated from the resonance and anti-resonance frequencies according to the standard circuit method. Furthermore, the dielectric constant (go/goo) and dielectric loss (tan6) are adjusted to IKHz.
Measured at the frequency of Examples are shown in Table 1, and comparative examples are shown in Table 2. Characteristics of samples with various compositions obtained in this way are shown using the general formula (Na, ~, Lix) (Nb, -y,
It is shown together with the x and y values in Sby)03. In Table 1, samples Nos. 1 to 15, which are examples of the present invention, all had crystal grain sizes of 10 French or less and had excellent piezoelectric properties.

On the other hand, in the comparative example shown in Table 2, y=0<
Samples Nos. 16 to 22 with a grain size of 0.001 had crystal grain sizes of more than 10 grains, ranging from 10 to 20 grains to 10 to 40 grains. Similarly, samples Nos. 24 to 28 where y=0.05>0.03 also had large crystal grain sizes. Also x
For sample number 1023 where =0.02<0.03, resonance-antiresonance could not be observed even after the above polarization treatment.
It was not possible to measure piezoelectric properties. x=0.15
Sample numbers 22 and 27 with >0.14 did not have a homogeneous phase as seen in the X-ray diffraction images. 1 2 All the samples shown in Table 1 have a specific gravity of 97% or more of the true specific gravity, and a frequency constant of 3.55-3.77 (KHz.m
) is within the range.

As is clear from Table 1 and the above characteristics, the piezoelectric porcelain according to the present invention has a small and uniform crystallite diameter, a large electromechanical coupling coefficient (Kp), and a dielectric constant (Kp).
) and has a large frequency constant, making it suitable as a piezoelectric ceramic for electromechanical transducers at high frequencies.

[Brief explanation of drawings]

FIG. 1 shows the composition range of the piezoelectric ceramic according to the present invention. 1 to 15: Examples, 16 to 27: Comparative examples. love/box

Claims (1)

[Claims] 1 (Na_1_-_x, Li_x) Nb_1_-_y
, Sb_yO_3, 0.03
Piezoelectric porcelain having a composition within the range of ≦X≦0.14, 0.001≦y≦0.03. 2 x, y are 0.03≦x≦0.10 and 0.002≦y≦0.01
, 0.10≦x≦0.14 and 0.002≦y≦0.03
The piezoelectric porcelain according to claim 1, having a composition in the range of .