JPS5941313B2 - oxide piezoelectric material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an oxide piezoelectric material, and more specifically to (Pb
The present invention relates to an oxide piezoelectric material having a basic composition represented by the general formula 3-yCay)[Me and Wc)xT1, -x]Os (where Me is any one of Co, Ni, and Mg).

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

For such uses, PbTiO3-PbZrO3 binary system and PbTiO3-PbZrO3-Pb (Mg-Nb
k--3) Cr2O3, MnO2, NiO in the 03 ternary system
Although materials with additives such as 2000-2000 added thereto have also been developed, these piezoelectric materials have a large dielectric constant of 350 to 2000, making them unsuitable for use in high frequency ranges. Furthermore, 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 have almost the same value, so spurious noise is likely to occur due to overtone of the coupling coefficient Kp in the spreading direction. existed. 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, a TbTiO3 yarn material with anisotropy of the coupling coefficient, in which the coupling coefficient Kt in the thickness direction and the coupling coefficient Kp in the spreading direction are significantly different, has been reported, but due to cracks that occur after sintering, It was not possible to obtain a large-sized sintered body, and the decomposition conditions were very severe, such as an applied voltage of 60 kV/cycle at 200° C., which made it easy to cause discharge breakdown, making it difficult to obtain a large-sized vibrator.

Furthermore, in conventional PbTiO3 materials, 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 coupling coefficient ratio Kt/Kp is about 4 to 6. Therefore, the spurious caused by the overtone of the coupling coefficient Kp in the spreading direction could not be ignored.

Furthermore, when attempting to apply the conventional TbTiO3 thread material as a surface wave element, it has been impossible to obtain a material with a surface wave temperature coefficient of 20 p.mu.m or less in a composition with a small dielectric constant of 200 or less.

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 a Funirite coil 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 negligible and extremely small.
Furthermore, the dielectric constant is small at less than 300, and sintering is possible at 1100℃.
50φ with less variation in composition due to Pb evaporation because it is possible at a low temperature below? The object of the present invention is to provide an oxide piezoelectric material that allows the above-mentioned large-sized vibrator to be obtained and that 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-YCa,)[(Me%W%)XTl
In the general formula of l-0')03 (where Me is any one of CO, Ni, and Mg), 0.10≦y≦0.30
, 0.01≦X≦0.10, and 0.2 to 3.0 weight of ZnO as a subcomponent. This is an oxide piezoelectric material containing additives.

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

For example, PbO, TiO2, CaCO3, NiO, wO
3. Accurately weigh raw material oxides such as cOO, MgO, and znO in a predetermined ratio, and mix them 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. Then, the mixture is heated to, for example, 600 to
It is pre-calcined at a temperature of about 900°C and is further ground into a prepared powder using a ball mill or the like. Thereafter, water or a binder such as polyvinyl alcohol is added to the prepared powder, and the powder is press-molded at a pressure of about 0.5 to 2 tons/CTIl, and then fired at a temperature of about 1000 to 1100°C. Firing is carried out in a closed furnace, and it is generally sufficient to maintain the maximum temperature for about 0.5 to 3 hours. Further, the present invention will be explained in detail.

First, (Pbl-, Ca,) [(Me%W%)XTil-
o') The reason for limiting the basic composition of 03 (Me is one of CO, Ni, Mg) to 0.10≦y≦0.30 is that the value of Kp is determined whether y<0.10 or y>0.30. This is because the signal becomes larger and more spurious signals occur.

Further, when y>0.30, the dielectric constant value becomes 300 or more, which is particularly disadvantageous for application as a surface wave element material or high frequency application. Moreover, the reason for limiting X2 to 0.01 to 0.10 is that when
This is because the effect of Me (Me is one of Nl, CO, and Mg) does not appear, and Kp becomes large when X>0.10.

Also, the amount of added ZnO, which is a subcomponent, is 0.2 to 3.0% by weight. The reason for this limitation is that the binding coefficient in the spreading direction is observed whether the addition amount is less than 0.2% or more than 30%.

Thus, according to the present invention, the following effects can be obtained.

First, in conventional PZT materials and ternary yarn materials, the values of the coupling coefficient Kt in the thickness direction and the coupling coefficient Kp in the spreading direction are almost the same, so when creating a vibrator using thickness vibration, the spreading On the other hand, 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 not confirmed. Therefore, the influence of spurious at high frequencies can be ignored. In particular, when the material of the present invention is used to create a vibrator for metal flaw detection, it becomes possible to create a transducer that uses only longitudinal waves without the influence of transverse waves. As described above, a vibrator piezoelectric ceramic material for a single mode transducer has not been previously reported and is a feature of the present invention. Second, P
By substituting a part of b with Ca, and by partially dissolving Pb (Me%Wψ03), which has a low firing temperature, the firing temperature can be lowered, improving the sinterability of the PbTiO3 thread material, and improving the sinterability of the PbTiO3 thread material. It became possible to obtain dense porcelain with a small bore that could be used for
bTiO3 yarn material has 60k/CTL at high temperature of 200℃
Since a sufficient coupling coefficient Kt cannot be obtained unless an electric field of 1 is applied, discharge breakdown is likely to occur during polarization, making it difficult to obtain a large oscillator.

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 polarization conditions of 100°C and 30 to 50 kV/Cm, resulting in discharge breakdown during polarization. Large oscillators can be produced stably with almost no occurrence of this phenomenon.

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

In the conventional PbTiO3 thread material, the PbTiO3 component is 60%.
The temperature coefficients of resonance frequencies in the m01% or higher region were all considered to have a negative tendency. In addition, it was thought that it was impossible to achieve a value of -20PF or less even if additives and solid solution components were added, but by replacing a portion of Pb with Ca'(1'10~15m01%), the temperature coefficient could be reversed. ±20P
It is also possible to obtain materials with temperature coefficients within P[11. 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 50k/(:Tn).
9) The piezoelectric properties were each measured by the standard circuit method shown in Nos. 1378 to 1395.

These measurement results are shown in Tables 1 to 4 along with the composition ratios of the sintered bodies. In addition, in these tables, F.
T is the firing temperature (O), D is the specific gravity (measured at 23°C), ε is the dielectric constant (1KI] measured at 23°C), Kt is the coupling coefficient (total) in the thickness direction, and Kp is the coupling in the spreading direction. Kt/Kp represents the coupling coefficient ratio.

Examples 9, 10, 11, 12, 13, 1 among these samples
When the changes in the coupling coefficients Kt and Kp and the coupling coefficient ratio Kt/Kp of the samples of Examples 4, 15, 16 and Reference Examples 1, 2, 3 and 4 were measured, the results shown in FIG. 1 were obtained.

In Figure 1, samples A, b, c, d, e, f, g, h,
are Examples 9, 10, 11, 12, 13, 14, 15, 1
6, sample 1, j, k, 1, reference example 1, 2, 3, 4,
are shown respectively.

As is clear from Figure 1, in the range of 0.10≦y≦0.30, although the coupling coefficient Kt shows a value of 50% or more, the coupling coefficient Kp is not confirmed and the coupling coefficient ratio Kt/Kp is infinite. Become. A piezoelectric ceramic material having only thickness vibration as described above has not been reported so far, which is a feature of the present invention. Figure 2 shows (Pbl-YCay) [(COqW%
)0.05Ti0.05))03 Fe2O3 in material
．． The coupling coefficients Kt, Kp and their ratios of materials added with 5 wf% are shown.

Although the coupling coefficient Kt is obtained at a value of 50% or more, the coupling coefficient Kp in the spreading direction is also 3 to 10%, which shows a different result from the addition of ZnO. Also, reference examples 7, 8, 9, 10,
In 11, 12, 13, 14, 15, 16, ZnO
We investigated the binding coefficients Kt and Kp of other additives, but found that the binding coefficient Kt was 50% or more, and we could not find any in which Kp was not confirmed. Figure 3 shows (Pbl-YSr
, ) [(CO%W%). ．． 05Ti0. , Coupling coefficient Kt, K of sample with 0.5 wt% ZnO added to ♂03 material
p, and its ratio Kt/Kp. Part of Pb is Sr
In the sample substituted with ZnO, even if ZnO was added, the coupling coefficient Kt was 50% or less, and the Kp was 10 to 15%. From these facts, it can be seen that a material in which a coupling coefficient Kt of 50% or more and a coupling coefficient Kp in the spreading direction are not confirmed can be obtained only by a material in which a part of Pb is replaced with Ca and ZnO is added. Figure 4 shows CaTiO in the case of X20.05.
3mOl% and the resonance frequency temperature coefficient Frt of the fundamental wave are shown.

In a composition range in which CaTlO3 is 10 to 15 m01%, a material with a temperature coefficient of ±20 pp[n or less can be obtained. In this way, a material with a small dielectric constant and an excellent temperature coefficient can be obtained.
FIG. 5 schematically shows the composition of the material according to the invention.

Thus, the oxide piezoelectric material according to the present invention can be said to be suitable for the following uses. 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 range.

Generally, impedance Z is Z=d/(2πf・ε・s)
(Here, d and s are the thickness and cross-sectional area of the sample, f is the frequency used, and ε is the dielectric constant.) Therefore, d needs to be made thinner in inverse proportion to f. In the end ZOO
l/(F2·ε·s), but as f becomes higher, the effect is squared, and Z rapidly decreases. For matching Z, s or ε
It is necessary to make ε small, but since there is a processing limit to s, 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 of that of conventional materials. Therefore, 10M with conventional materials
If it can be used up to Hz, if the material of the present invention is used, it can be used up to 50M.
This is possible up to about Hz. In addition, the coupling coefficient ratio Kt/Kp
is infinitely large, so the influence of spurious effects due to Kp overtones is negligibly small, which is practically advantageous when creating a vibrator.

2) Probe for linear scan type ultrasound diagnostic equipment.

As the frequency increases, sonic wave transducing elements in probes for ultrasonic diagnostic apparatuses are required to be larger in size and thinner. It was difficult to reduce the size and thickness of the device with conventional PbTiO3 thread piezoelectric materials, but the material of the present invention has good sinterability, so it is possible to make the device large and thin with excellent mechanical strength (for example, (Length 50-100m, Width 15-20m, Thickness 200μm)
is easily realized. 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 (less than 20 ppm). (desirable).

Furthermore, when using a material with a high dielectric constant, the impedance of the elastic surface wave filter becomes small, causing a problem of mismatching with an external circuit. For this reason, it is desirable that the value of the dielectric constant be as small as possible.5j1. ing. In response to these requirements, PbTiO3-PbZrO3 yarn material (PZT material) and PbTiO3-PbZrO3 yarn material (PZT material)
Attempts have been made to use bTlO3-PbZrO3Pp (Sn/Sb%)03 yarn materials (ternary yarn materials), but these materials have dielectric constants of 350 to 1000 in the region where the temperature coefficient is 20 ppm or less, and surface waves The drawback was that the dielectric constant was too high to be used as a 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, a temperature coefficient of resonance frequency within ±20 PPf1, and excellent aging characteristics.

As described above, it can be seen that the use of the piezoelectric material of the present invention is useful for applications that were previously impossible.

[Brief explanation of the drawing]

The drawings are for explaining the characteristics of the oxide piezoelectric material according to the present invention, and FIG. 1 shows the mol. and coupling coefficients Kt(to), Kp((
70) and their ratios, Figure 2 is a relationship curve diagram between the mole e of CaTiO3 and the coupling coefficients Kt (%), Kp (%), and their ratios when Fe2O3 is included as a subcomponent, and Figure 3. is SrT when part of Pb is replaced with Sr
The relationship curve between the mol% of iO3, the binding coefficients Kt (%), Kp (to), and their ratios, Figure 4 shows the mol% of CaTlO3? FIG. 5 is a ternary diagram showing the composition range of the present invention.

Claims (1)

[Claims] 1 (Pb_1_-_yCa_y) [Me_1_/_2
It is expressed by the general formula W_1_/_2)_xTi_1_-_x)O_3 (where Me is any one of Co, Ni, and Mg), and 0.1≦y≦0.30, 0.01≦x≦0.
An oxide piezoelectric material having a basic composition of 10 and further containing 0.2 to 3.0% by weight of ZnO as a subcomponent.