JPS6022837B2 - oxide piezoelectric material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to oxide piezoelectric materials, particularly (11x)PbT
This invention relates to improvements in oxide piezoelectric materials having a basic composition of j03-xSrTi032 components.

As is well known, piezoelectric materials are used in a wide range of fields as elements such as ultrasonic vibrators, mechanical filters, ceramic resonators, vibrometers, and accelerometers.
For such uses, the 3-binary system of PbTi03-PbZ and the 3-Pb (MgI/state b2/
3) Bi203, Cr203, Mh02 in 03Z ternary system
, Ni0 and other additives have been developed, but these electrostatic materials have a rape electrostatic Curie temperature of 30 picoC.
It could not be used at higher temperatures. Further, the piezoelectric material has a slope ratio of 100, making it unsuitable for use in the high frequency 2 range.

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 there is a drawback that spurious noise is likely to occur due to overtone of the coupling coefficient Kp in the spreading direction. Were present. For this reason, in high frequency applications, it has been considered desirable to have a Kt/Kp ratio of about 3.0 or more. In addition, PbTi03-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, but due to cracks that occur after being cut, the diameter of It was not possible to obtain a large Akatsuki crystal as described above, and the polarization conditions were extremely severe, with an applied voltage of 6 V at 200°C, making it easy to cause discharge breakdown and making it difficult to obtain large oscillators. there were.

Also, PbTiQ-SrTiQ-based materials have been reported, but when no subcomponents are added, PbTi03 is 75%.
With the above, scale twilling was considered impossible, and it was impossible to create a vibrator that could be put to practical use.

The purpose of the present invention is to solve the above-mentioned problems.It has a high Curie temperature, can be used stably even at high temperatures of 300°C or higher, and has a sufficient value for the coupling coefficient Kt in the thickness direction and the coupling coefficient Kp in the spreading direction. It has anisotropy with a yield rate of 180~2
The object of the present invention is to provide an oxide piezoelectric material that is as small as 500 mm and easy to crystallize, making it possible to obtain large oscillators of 500 mm or more, and that is much easier to polarize than conventional PbTi03 materials.

The present invention is (Pb, -xSrx)Ti03x=0.01
~0.20, and as a subcomponent, Mg0
, Zn○, Cr203, Ayu203, Ga203, Ta
At least one of 203 is 0.1 to 2. % by weight of oxide piezoelectric material. Such an oxide piezoelectric material of the present invention can generally be easily manufactured by a powder metallurgy method.

For example, Pb○, Ti02, SrCQ and Mg0, Zn
○, Cr203, A&03, Ga203, Ta203, and other raw material oxides are accurately weighed out 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 converts into an oxide upon heating, such as a hydroxide, carbonate, or oxalate.

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 a prepared powder.

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 0.5 to 1000 degrees Celsius, followed by firing at a temperature of approximately 1000 to 1250 degrees Celsius. During this firing, there is a risk that some of the Pb○, which is one of the components, may evaporate and dissipate, so the firing is carried out in a closed furnace, and the maximum temperature is generally maintained at 0.5~
About 3 hours is sufficient. Furthermore, the present invention will be explained in detail.

First, the reason for limiting x to 0.01 to 0.20 in the basic composition of (1-x)PbTi03-NateTi03 is that x<0
．． 01 has poor cupping properties and cannot produce delicate porcelain x>0
．． At 20, the Curie temperature drops below 350oo, and at 3
This is because it cannot be stably used at high temperatures of 00° C. or higher, and the coupling coefficient Kp in the spreading direction increases, and the coupling coefficient in different directions becomes smaller.

Further, the dielectric constant is 250 or more, making it difficult to use in a high frequency range.

In addition, the subcomponents Mg○, Zn○, Cr203, A〆2
03, Ga203, T also has an additive content of 03 of 0.1 to 2.
．． The reason for this is that if the content is less than 0.1% by weight, the effect of these effective ingredients in improving the coagulation properties and polarization properties of PbTi03-based ceramics cannot be obtained;
This is because if the amount exceeds % by weight, the specific resistance of the porcelain will decrease, making it difficult to apply a sufficient electric field. Thus, the following effects can be obtained by the present invention.

First, PbTi03 had a Curie temperature of around 500 oo and was considered to be a promising piezoelectric material, but it was not practical due to its poor crystallization properties.In contrast, in the present invention, SrT
In particular, iQ is used as one component, and Mg0, Zn○, Cr203, A203, Ga are used as subcomponents.
Since 2Q and Ta203 are added, on the one hand they act as a hardening agent and facilitate hardening.

This facilitation of dawning eventually lowers the dawning temperature, suppressing the evaporation of Pb, which forms part of the composition, and
Finally, a large and dense piezoelectric material can be easily obtained. Second, the oxide piezoelectric material according to the present invention is
It is possible to easily polarize PbTi03 ceramic, which has been difficult to polarize in the past.

That is, while the conventional PbTi03-based ceramic required a voltage of 60 to 80 KV/K at a high temperature of 180 to 20 P○ as polarization conditions, the piezoelectric material of the present invention
Sufficient polarization can be achieved under relaxed conditions of 0 qo and 40 to 6 thigh V/en. Therefore, discharge breakdown during polarization is less likely to occur, and a large oscillator can be easily obtained. Thirdly, by substituting a part of Pb with Cr, changes in mechanical strength over time after polarization can be improved. In other words, with the conventional PbTi03 material, the mechanical strength decreased approximately 1000 hours after polarization, causing cracks and making it difficult to create large oscillators, whereas the material of the present invention significantly improves this. It has the effect of simmering.

Next, examples of the present invention will be described.

The assembled samples were divided into 200×1. After polishing, baking silver electrodes on both sides and polarizing at 100°C and 6 plate V/g, Proc. IRE. Vo〆. 137 (1 place 9) 13
The piezoelectric properties were each measured by the standard circuit method shown in No. 78-1395.

The results of these measurements are shown in Table 1 together with the composition ratio of the aggregates. In addition, in Table 1, F. T. is the firing temperature (00), D is the specific gravity (measured at 23℃), and is the dielectric constant (I
Kt is the coupling coefficient in the thickness direction (%
), Kp indicates the coupling coefficient (%) in the spreading direction, Kt/Kp indicates the ratio of coupling coefficients, and Tc indicates the Curie temperature (00), respectively.

Table 1 Among these samples, the values of the electromechanical coupling coefficient Kt depending on the polarization temperature were measured for the samples of Example 20 and Reference Example 2, and the results shown in FIG. 1 were obtained.

In FIG. 1, curve a shows the case of Example 20, and curve b shows the case of Reference Example 2. 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 the 03 series ceramic, and polarization is easier. Next, among these samples, changes in coupling coefficients Kt and Kp of Examples 2, 9, 20, 27 and Reference Examples 7 and 8 and Kt/
When the ratio of Kp was measured, the results shown in FIG. 2 were obtained.

In Fig. 2, samples a, b, c, and d are Examples 2, 9, and 2.
0 and 27 are samples e and f are reference examples 7 and 8, respectively.

When SrTi03 is 2.0% or less, Kp is 15% or less and the Kt/Kp ratio is 3.0 or more, indicating that the anisotropy of the coupling coefficient is sufficiently large. Furthermore, when the change in the electromechanical coupling coefficient Kt of Examples 9 and 2 and Combined Consideration Example 7 among these samples with respect to temperature was measured, the results shown in FIG. 3 were obtained. In FIG. 3, curve a corresponds to curve b for Example 9.
Curve c shows the case of Example 20, and curve c shows the case of Reference Example 7.
According to this figure, since both Examples 9 and 20 of the present invention have high Curie temperatures, Kt is almost constant over a wide temperature range from room temperature to 35,000. This result shows that the piezoelectric material according to the present invention can be used at the highest operating temperature for a piezoelectric material. In addition, SrTi0 in these sample samples
When the haze ratios of Examples 2, 13, 19, 27 and Reference Examples 7 and 8 having different moc% of 3 were measured, the results shown in FIG. 4 were obtained. In FIG. 4, a, b, c, and d represent Examples 2, 13, 19, and 27, respectively; e and f represent Reference Example 7;
8 is shown. The dielectric constant value of SrTi03 is 250 or less when the temperature is 2°C or less, which is sufficiently small compared to the 100°F of ordinary PZT, and is advantageous in high frequency applications.

Figure 5 shows the composition of Example 1 and Reference Example 2 with a diameter of 5. Create a melon disc oscillator and show the mechanical strength after polarization t
The results of examining changes in an6 over time are shown.

In FIG. 5, curve a is Example 13 and curve b is Reference Example 2.
Each case is shown below. Reference example 2 without Sr substitution
With the composition of Example 13, the n6 value rapidly increased and cracks appeared in the vibrator after 10 feeding hours after polarization, whereas in the case of Example 13, no change in the n6 value was observed, and the mechanical strength decreased due to Sr substitution. This shows that the change over time has been improved.

As is clear from the above examples, the piezoelectric material according to the present invention has many advantages, such as being able to be used stably even at high temperatures of 300 qo or more, and being usable in a high frequency range. Furthermore, since the polarization conditions are easy, it is possible to create large-sized resonators, and the change in mechanical strength over time is also excellent, making it possible to demonstrate the excellent functions of PbTi03 material, which has had limited applications up until now. Thus, the oxide piezoelectric material according to the present invention can be said to be suitable for the following uses, for example.

(1) Vibration, acceleration, and pressure measurements of high-temperature objects. Vibration and acceleration of objects that reach temperatures close to 500 degrees or that experience rapid temperature changes can be measured.

Similarly, pressure inside hot objects can be measured. ■ Ultrasonic application for high-temperature objects It can be used as an ultrasonic source during ultrasonic processing of high-temperature objects, or as an element for ultrasonic inspection of high-temperature objects.

Rigid Generation of powerful ultrasonic waves Normal piezoelectric materials generate heat when operated with large amplitude, making them unusable, but the piezoelectric material according to the present invention has three
Since it can withstand use at zero and above zero, it is advantageous for generating powerful ultrasonic waves through large amplitude operation.

{41 Application in High Frequency Conventional piezoelectric materials have a dielectric constant of 100 degrees Fahrenheit, which is too large, making them unsuitable for use in the high frequency range.

Generally, impedance Z is Z=d/(2mf・go・s)
(Here, d and s are the thickness and cross-sectional area of the sample, f is the frequency used, and d is the dielectric constant.) Therefore, d is f
It is necessary to make it thinner in inverse proportion to . After all ZQI/(f2
・go・s) However, as f becomes higher, Z becomes effective as a square and rapidly decreases. Although it is necessary to make the s cage small for Z matching, there is also a processing limit on s, so it is more advantageous to make the cage smaller. The piezoelectric material of the present invention has a dielectric constant of 150 to 25, which is 1/5 that of conventional materials.
~1/10. Therefore, if the conventional material can be used up to 1mMHz2z, the material of the present invention can be used up to about 50MHz. '5' Linear Scan Type Ultrasonic Diagnostic Probe Sonic transducer elements in probes for ultrasonic diagnostic equipment are required to be larger in size and thinner as the frequency becomes higher.

It was difficult to make the element larger and thinner with conventional piezoelectric materials, but the material of the present invention has good accretion properties, so it can be made into a large and thin plate with excellent mechanical strength (for example, a length of 50 mm). ~l
(overboard, width 15-20 mm, thickness 200 mm) can be easily realized. 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 drawings]

The drawings show characteristic examples of the oxide piezoelectric material according to the present invention. Fig. 1 shows the relationship between polarization temperature and electromechanical coupling coefficient Kt (%), and Fig. 2 shows the relationship between the number of moles of SrTi03 and electromechanical coupling. Figure 3 is a relationship curve between coefficient Kt (%) Kp (%) and their ratio. Figure 3 is a relationship curve between temperature and electromechanical coupling coefficient Kt (%). Figure 4 is a relationship curve between the number of moles of SrTi03 and permittivity. 5 and 5 respectively show curve diagrams of the relationship between time and n6. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5

Claims (1)

[Claims] 1 (1-x)PbTiO_3-xSrTiO_3 system 2
The component material has a composition of x=0.01 to 0.20, and MgO, ZnO, Cr_2O as subcomponents.
An oxide piezoelectric material characterized in that 0.1 to 2.0% by weight of at least one of Ga_2O_3, Ga_2O_3, and Ta_2O_3 is added.