JPS5941310B2 - oxide piezoelectric material - Google Patents

Description

[Detailed description of the invention] The present invention relates to oxide piezoelectric materials.

For more details, see (Pbl-aCaafu [(Me1/3
Nb2/3fu x Til-x] 03 series basic set 15, (Me is either Mg or Zn) 0.01≦x
The present invention relates to an oxide piezoelectric material having a composition range of ≦0.10, 0.05≦a≦0.35. Furthermore, as by-products, MnO and N
at least one of i0 and Fe2O3 from 0.05 to 2
．． The present invention relates to an oxide piezoelectric material containing 0% by weight.

Recently, various ultrasonic transducers and surface wave elements using oxide piezoelectric materials have been developed.

For such applications, PbTiO3-PbZr03:
elemental system or PbTiO3-PbZr03-Pb (Mgl/3
NbSi) Cr2O3, MnO2, NiO in the 03 ternary system
Although materials with additives such as 100% and 100% have been developed, these piezoelectric materials have a large dielectric constant of 350 to 2000, making them unsuitable for use in high frequency ranges. In addition, when these materials are used at high frequencies, the coupling coefficient Kt in the thickness direction and the coupling coefficient Kp in the spreading direction are approximately the same value, so spurious signals are likely to occur due to overtones of the coupling coefficient Kp in the spreading direction. Were present. For this reason, it has been considered desirable for the Kt/Kp ratio to be as large as possible in high frequency applications. In addition, PbTiO3-based materials have been reported that have coupling coefficient anisotropy in which the values of the coupling coefficient Kt in the thickness direction and the coupling coefficient Kp in the spreading direction are significantly different.
Due to cracks that occur after sintering, it is not possible to obtain large sintered bodies with a diameter of 20 mm or more, and the polarization conditions are extremely severe, with an applied voltage of 60 KV at 200°C, which tends to cause discharge breakdown and generate large vibrations. In addition, it is difficult to obtain offspring using conventional PbTi0.

In the material, the coupling coefficient Kt in the thickness direction is 40 to 48%, and the coupling coefficient Kp in the spreading direction is 8% or more, so the limit for the ratio of coupling coefficients Kt/Kp is about 4 to 6, and the coupling coefficient in the spreading direction is 40 to 48%. The spurious caused by Overton's coefficient Kp could not be ignored. Furthermore, when trying to apply conventional PbTi03-based materials as surface wave elements, the dielectric constant is 2.
Surface wave temperature coefficient of 20p for small compositions below 00
It was not possible to obtain a material with a diameter of less than μm.

Furthermore, the temperature coefficients of these materials all tend to be negative, and it has not been possible to improve the temperature coefficients by using ferrite coils or the like. The purpose of the present invention is to solve the above problems, and the coupling coefficient Kt in the thickness direction is as large as 50% or more, and the coupling coefficient Kp in the spreading direction is 3 to 5%, that is, Kt/Kp is 10 to 19. It has a low dielectric constant of 300 or less and is easy to sinter, making it
The present invention provides an oxide piezoelectric material in which a large-sized vibrator of 0 (!) (177!) or more cannot be obtained and which is much easier to polarize than conventional PbTiO3 materials.

Furthermore, in the material of the present invention, it is also possible to obtain a material with an excellent surface wave temperature coefficient.

The present invention provides (Pbl-ACaa) [(Mel/3Nb2/
3) In the general formula of XTil-o]03 (where Me is either Mg or Zn), 0.05≦a≦0.2
5, an oxide piezoelectric having a composition of 0.01≦x≦0.10, and optionally containing at least one of MnO, NiO, and Fe2O3 as a subcomponent in an amount of 0.05 to 2.0% by weight. It is the material.

Such an oxide piezoelectric material of the present invention can generally be easily manufactured by a powder metallurgy method.

For example, PbO, TiO2, CaCO3, MnCO3,
Raw material oxides such as NlO, Fe2O3, Nb2O5, MgO, and ZnO are weighed out accurately in predetermined proportions and mixed well using a ball mill or the like. Note that the raw material used at this time may be a compound that is converted into an oxide by heating, such as a hydroxide, a carbonate, an oxalate, or the like. Next, the mixture is preliminarily calcined at a temperature of, for example, about 600 to 900° C., and further pulverized using a ball mill or the like to obtain prepared powder wood.

Thereafter, water or a binder such as polyvinyl alcohol is added to the prepared wood powder, pressure molded at a pressure of about 0.5 to 2 tons, and then fired at a temperature of about 1100 to 1200°C. During this firing, there is a possibility that some of the PbO, which is one of the components, may evaporate or diffuse, so the firing is carried out in a closed furnace, and the maximum temperature is generally 0.5~3.
About an hour is enough. Further, the present invention will be explained in detail. First (Pbl-ACaa) [Mel/3Nb2/3)
XT! 1-X') 03 basic composition (Me is Mg, Z
The reason for limiting 0.05≦a≦0.35 for n) is that Kp
This is because the value of Kt/Kp becomes 5% or more, and the ratio of Kt/Kp becomes less than 10, which increases the occurrence of spurious signals.

Further, if a>0.35, the dielectric constant value becomes 300 or more, which is particularly disadvantageous for application as a surface wave element material or high frequency application. The reason for limiting X to 0.01 to 0.10 is that when X is 0.01, Pb (Mel/3Nb2/3
)03 (however, Me is either Mg or Zn), the effect does not appear, and when x>0.10, Kp increases and Kt/
This is because the ratio of Kp is less than 10.

In addition, the content of any one of MnO, NiO, and Fe2O3 was limited to 0.05 to 2.0% by weight.
If it is less than 5% by weight, the remarkable effect of these subcomponents of improving the sinterability and polarization characteristics of PbTiO3 magnetism cannot be obtained, and if it is more than 2.0% by weight, the sinterability of the porcelain becomes worse. This is because something happened.

Thus, the following effects can be obtained by the present invention.

First, in conventional PZT materials and three-component materials, the coupling coefficient Kt in the thickness direction and the coupling coefficient Kp in the spreading direction are almost the same. However, in the material of the present invention, the coupling coefficient in the thickness direction shows a large value of 50% or more, but the coupling coefficient Kp in the spreading direction is 3~~. Since the value is as small as 5%, spurious waves at high frequencies are small, which is advantageous in practice. Secondly, by replacing a part of Pb with Ca, Pb (Mel/3Nb2/3) with low firing temperature
By dissolving a part of 03 as a solid solution, the firing temperature is lowered, and P
By improving the sinterability of bTiO3-based materials, it becomes possible to obtain dense magnetism with fewer bores that can be used in surface wave fundamental materials. In addition, the PbTiO3
With this type of material, it is impossible to extract a sufficient coupling coefficient Kt unless an electric field of 60 KV is applied at a high temperature of 200°C, so there is a drawback that discharge destruction occurs easily during polarization and it is difficult to obtain large oscillators. .

In the material of the present invention, since a part of Pb is replaced with Ca, polarization becomes easy, and a sufficient coupling coefficient Kt can be obtained under the polarization conditions of 100°C and 30 to 50 KV, so that discharge breakdown during polarization is prevented. Large oscillators can be created stably with almost no occurrence.

Thirdly, by adding at least one of MnO, NiO, and Fe2O3, it is possible to further improve the sinterability, polarization characteristics, and resonant frequency characteristics over time.

Fourthly, in the material system of the present invention, it is also possible to obtain a material with a small temperature coefficient of the resonance frequency of the fundamental wave.

In conventional PbTlO3-based materials, the PbTiO3 component is 60%
The temperature coefficients of resonance frequencies in the region of m0t% or higher were all considered to have a negative tendency. In addition, it was thought that it was impossible to achieve a value of -20 ppm or less even if additive solid solution components were added, but it is possible to reverse the temperature coefficient by substituting 10 to 15 m0t% of C for part of the Pb. It is also possible to obtain materials with temperature coefficients within ±20 ppm. This phenomenon is not observed in substitutions such as Mg, Sr, Ba, etc., and is a phenomenon peculiar to Ca.

Next, examples of the present invention will be described.

The sintered sample was polished to a size of 20φ x 0.5mm, and electrodes were baked on both sides and polarized at 100°C and 50KV, followed by PrOc, RE. VOtl37 (1949) 137
The piezoelectric properties were each measured by the standard circuit method shown in Nos. 8 to 1395.

These measurement results are shown in Table 1 together with the composition ratio of the sintered bodies. In addition, in Table 1, F. T is the firing temperature C
C), D is the specific gravity (measured at 23°C), and ε is the dielectric constant (1K
Kt is the coupling coefficient in the thickness direction (2)
, Kp is the coupling coefficient in the spreading direction (Fji is Kt/Kp
respectively indicate the ratio of coupling coefficients. Among these samples, the values of the electromechanical coupling coefficient Kt depending on the polarization temperature were measured for the samples of Example 15 and Reference Example 1, and the results shown in FIG. 1 were obtained.

In FIG. 1, curve a shows the case of Example 15, and curve b shows the case of Reference Example 1. Embodiments of the present invention utilize conventional PbTi
It can be seen that a sufficient coupling coefficient Kt can be obtained even at a low temperature compared to O3-based ceramics, and polarization is easier. Next, conduct 9 in these samples 9, 10, 1111
2, 13, 14, 15, 16 Changes in coupling coefficient KtxKp and coupling coefficient ratio Kt/Kp of samples of Reference Examples 112, 3, and 4
When measured, the results shown in Figure 2 were obtained.

In FIG. 2, sample A. b,. c,. d,. e. flg
、． h is Example 9, 10111112, 13, 14, 1
5, 16 as samples 1, . j,. k11 is reference example 112, 3
, 4 are shown respectively.

As is clear from Fig. 2, in the range of 0.05≦a≦0.35, the coupling coefficient Kt shows a value of 50% or more, but the coupling coefficient Kp is as small as 3 to 5%, and the coupling coefficient ratio Kt
/Kp reaches 10-19.

Figure 3 shows CaTiO3mO in the case of x-0.05.
The relationship between the dielectric constant ε and the dielectric constant ε is shown. The dielectric constant shows a small value of 300 or less when a is 0.35. Figure 4 shows CaTiO3mO! in the case of x=0.05! ! It shows f% and the resonant frequency temperature coefficient of the fundamental wave. CaTiO3 is 10-15m0
In the composition range of t, a material with a temperature coefficient of ±20 ppm or less can be obtained. In this way, a material with a dielectric constant of 200 or less and an excellent temperature coefficient can be obtained. Thus, the oxide piezoelectric material according to the present invention can be said to be suitable for the following uses, for example.

1) Application in high frequencies Conventional piezoelectric materials have a dielectric constant of about 1000, which is too large, making them unsuitable for applications in the high frequency range5.

Generally, impedance Z is Z=d/(2πf・ε・s)
(Here, d-s is the thickness of the sample, and the cross-sectional area f is the frequency used.
ε is the dielectric constant. ) is given by Therefore, d needs to be made thinner in inverse proportion to f. After all ZCX) 1/q
(F2.ε·s), but as i becomes higher, Z becomes effective as a square and rapidly decreases. It is necessary to make s or ε small for Z matching, but since s also has a processing limit, it is advantageous to make ε small. The piezoelectric material of the present invention has a dielectric constant ε of about 180 to 300, which is 1/3 to 1/10 as compared with conventional materials. Therefore, 10MH with conventional materials
If the material of the present invention can be used up to 50MH
It is possible up to about z. Further, since the coupling coefficient ratio Kt/Kp is as large as 10 to 19, the influence of spurious noise due to overton of Kp is small, which is practically advantageous when producing a vibrator.

2) Probe for linear scan type ultrasound diagnostic equipment.

As the frequency becomes higher, the sound wave transducing element in a probe for an ultrasonic diagnostic apparatus is required to have a large size and a thin plate. It was difficult to reduce the thickness of large-sized elements with conventional TbTiO3-based piezoelectric materials, but the material of the present invention has good sinterability, so it is difficult to reduce the size of large-sized thin plates with excellent mechanical strength (e.g., length 50~00mms width 15~20mj thickness 200μm)
is easily realized. 3) Application as a substrate for surface waves Recently, surface wave filters using oxide piezoelectric materials have been developed, but the characteristics particularly required for piezoelectric materials for surface waves are a small temperature coefficient of surface waves (20 ppm or less). desirable).

Furthermore, when using a material with a high dielectric constant, the impedance of the surface acoustic wave filter becomes small, causing a problem of mismatching with an external circuit. For this reason, it is considered desirable that the value of the dielectric constant be as small as possible.

In response to these requirements, PbTiO3-PbZrO3-based materials (PZT materials) and PbTiO3-PbZrO3-Pb
(Snl/2Sb1/2)03 series materials (ternary materials) have been tried, but these materials have a temperature coefficient of 2.
In the region of 0 ppm or less, the dielectric constant is 350 to 1000, which has the disadvantage that the dielectric constant is too large to be used as a surface wave filter material. In addition, these materials had drawbacks in stability due to large changes in resonant frequency over time. By using the material of the present invention, it is also possible to obtain an oxide piezoelectric material suitable for surface waves, which has a small dielectric constant of 200 or less, a temperature coefficient of resonance frequency within ±20 ppm, and excellent aging characteristics.

As described above, the piezoelectric material of the present invention can be used for applications that were previously impossible.

[Brief explanation of the drawing]

The drawings show characteristic examples of the oxide piezoelectric material according to the present invention. FIG. 1 is a graph showing the relationship between polarization temperature and electromechanical coupling coefficient Kt, and FIG.
Figure 3 is a diagram of the relationship between Kp (%) and its ratio.
A relationship curve diagram between mol% of TiO3 and dielectric constant ε, Figure 4 is C
FIG. 5 shows a relationship curve between the mol% of aTiO3 and the temperature coefficient of resonance frequency, and FIG. 5 shows a ternary diagram showing the scope of claims.

Claims (1)

[Claims] 1 (Pb_1_-_aCa_a) [Me1/3Nb2
/3)_xTi_1_-_x] O_3 basic composition (Me is either Mg or Zn) x = 0.01 ~
0.10, and a=0.05 to 0.35. 2 MnO, NiO and Fe_2O_3 as subcomponents
The oxide piezoelectric material according to claim 1, characterized in that it contains 0.05 to 2.0% by weight of at least one of the following.