JPS6132838B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention is based on Pb(Y1/2Nb1/2)O ₃ −PbTiO ₃ −
This invention relates to an oxide piezoelectric material suitable for ultrasonic transducer materials, piezoelectric buzzer materials, etc. whose basic composition is a three-component solid solution composed of PbZrO ₃ . As is well known, so-called Pb is a solid solution of PbTiO ₃ and PbZrO ₃ with approximately equimolar composition.
(TiZr)O ₃ -based oxide piezoelectrostrictive materials have superior properties compared to piezoelectric materials such as BaTiO ₃ and are used as electro-mechanical transducers, electro-acoustic transducers, etc. In addition, three-component piezoelectric materials in which Pb(CoW)1/2O ₃ or the like is fixed, and materials in which MnO ₂ or NiO are added to these materials are also widely used. However, there are some problems in terms of characteristics when using these ferroelectric materials as ultrasonic vibrators or piezoelectric buzzer vibrators. In other words, there is a strong demand for miniaturization of recent electronic circuit components, and there is also a strong trend toward higher operating frequencies, but as is well known, the resonant frequency of a piezoelectric vibrator is an inverse function of its shape; Then, the shape of the vibrator becomes smaller and thinner, and not only its electrical properties but also its mechanical strength becomes a problem in the processing or assembly process. Generally, when adding additives to Pb(TiZr)O ₃ systems to improve their properties, the additives are divided into two groups depending on their effects. The first group is
When MnO, Fe ₂ O ₃ , Cr ₂ O ₃ , CoO, etc. are added, the coercive electric field generally increases and the piezoelectricity decreases, but the mechanical quality factor Qm increases and the material becomes a so-called hard material. The second group is La ₂ O ₃ ,
Adding Nb ₂ O ₅ , WO ₃ .Ta ₂ O ₃ , etc. reduces the coercive electric field, making polarization easier and improving piezoelectricity, but Qm decreases and the material becomes a so-called soft material. High Qm materials have excellent mechanical strength and do not suffer from a decline in manufacturing retention even when thinned.
Soft materials with a Qm of 100 or less have weak mechanical strength and have a low yield when thinning. However, for example, materials with low Qm are preferable as materials for speakers because they provide a soft tone when making a piezoelectric buzzer vibrator and can be used to widen the frequency band. Therefore, a piezoelectric material with low Qm, excellent mechanical strength, and easy processing into thin sheets has been desired. To explain more specifically, there are various methods for obtaining ceramics in the form of thin plates of about 100 μm, but the method of forming ceramics using a doctor blade method and firing them is the best.
It is advantageous in terms of productivity and cost, and is becoming mainstream. However, conventional PbTiO ₃ −
Part of Pb in PbZrO ₃ −Pb(Y1/2Nb1/2)O ₃
Materials partially substituted with Ba, Sr, or Ca are
With a Qm of 100 or less, it is suitable as a vibrator material for piezoelectric buzzers, but it does not have sufficient mechanical strength when producing thin plate vibrators of about 100 μm, and the yield will be greatly reduced due to cracks and chips during processing. In addition, as resonators become thinner, the conventional electrode construction method of applying silver paste and firing causes a significant decrease in the electromechanical coupling coefficient and dielectric constant of the resonator due to penetration of the frit components of the silver paste. . For this reason, methods of forming electrodes using nickel plating or the like are becoming mainstream. However, in this case too, the conventional PbTiO ₃ −
Part of Pb in PbTiO ₃ −Pb(Y1/2Nb1/2)O ₃
In materials partially substituted with Ba, Sr, or Ca, electrode short-circuits occur due to penetration of the plating plate, which has become a practical problem. The present invention improves the above drawbacks, and the value of Qm is 100.
The object of the present invention is to provide an oxide piezoelectric material that is useful as a piezoelectric buzzer resonator material and has excellent mechanical strength despite being the following material. The oxide piezoelectric material according to the present invention has a basic composition of
_PbTiO3 40.0-50.0 mol%, _PbTiO3 45-59.5 mol% and Pb(Y1/2Nb1/2) _O3 0.5-5.0 mol%
A solid solution consisting of 10 mol % or less of Pb in its composition is replaced with one or a combination of two or more of Ra, Sr, and Ca, and In ₂ O ₃ ,
At least one selected from MgO, Sb ₂ O ₃ from 0.1 to
It is characterized by containing 1.0% by weight. PbTiO ₃ PbZrO ₃ which is the main component in the present invention
−Pb(Y1/2Nb1/2)O ₃ ternary system composition ratio
The reasons for limiting PbTiO3 _to 40.0 to 50.0 mol%, PbZrO3 _to 45 to 59.5 mol%, and Pb(Y1/2Nb1/2)O3 _to 0.5 to 5.0 mol% are as follows. _PbTiO3 is
Even if it is less than 40 mol% or more than 50 mol%, the desired electromechanical coupling coefficient (KP) and dielectric constant (ε) cannot be obtained. Also, Pb(Y1/2Nb1/2)O ₃ is 0.5
If it is less than 5 mol %, there is hardly any effect of improving sinterability, and if it is less than 5 mol %, it is difficult to obtain a uniform solid solution and the electromechanical coupling coefficient (KP) decreases.
Therefore, PbTiO ₃ and Pb(Y1/2Nb1/2)O ₃ are selected within the above range, and the rest is PbZrO ₃ . In addition, the reason why we limited Pb in the composition to 10 mol% or less by one type or a combination of two or more of Ba, Sr, and Ca is that if it exceeds 10 mol%, sinterability deteriorates, and the bonding This is because the coefficient (KP) also decreases. Furthermore, additives In ₂ O ₃ , MgO,
The reason why the amount of Sb ₂ O ₃ added was limited to 0.0 to 1.0% by weight is that if it is less than 0.1% by weight, there is almost no effect on improving mechanical strength by improving sintered density.
If it exceeds 1.0% by weight, it will not dissolve uniformly and will partially precipitate, resulting in a decrease in the mechanical strength of the material and a decrease in the bonding coefficient KP.
This is because it is no longer sufficient. The oxide piezoelectric material of the present invention can generally be easily manufactured by a non-powder metallurgy method. For example, PbO,
TiO ₂ , ZrO ₂ , Y ₂ O ₃ , Nb ₂ O ₃ , MgO, Sb ₂ O ₃ ,
Raw material oxides such as SrCO ₃ , CaCO ₃ , BaCO ₃ and the like are accurately weighed in a predetermined ratio and mixed using a ball mill or the like. Next, this mixture is preliminarily calcined at a relatively low temperature, for example, 600 to 900°C, and further pulverized using a ball mill or the like to obtain a prepared powder. After that, water or a binder such as polyvinyl alcohol is added to this adjusted powder to form a powder of 0.5 to 1.0 tons/
After pressure molding at a pressure of about cm ² , it is fired at a temperature of about 1120 to 1180°C for about 0.5 to 3 hours. For example, a pair of electrodes is provided on both sides of the sintered body thus obtained by well-known means, and a DC electric field of 20 to 30 kV/cm is applied.
Polarization can be achieved by applying the voltage in silicone oil at about 80 to 120°C for about one hour. After polarization is performed as described above, aging is performed at 100°C for 24 hours and then left at room temperature for 24 hours. In order to evaluate the piezoelectric properties of the piezoelectric substrate obtained in this way, the electromechanical coupling coefficient in radial vibration was
KP was measured. This measurement followed the IRE standard circuit method. In addition, the dielectric constant ε was measured at a frequency of 1kHz using a capacitance bridge. The measurement of Qm was calculated using the following formula. Qm = 1/4π・C・R ( _a − _r ) where _a = anti-resonant frequency _r = resonant frequency C = capacitance R = resonant resistance To measure the bending strength, use a piezoelectric ceramic disc with a diameter of 25 mm and a thickness of 1.6 mm. Both sides were ground to a thickness of 1 mm to give a mirror finish. Then, a 3 mm wide sample plate was cut from the center of each disk using a diamond cutter, and the cut surface was sanded with SiC sand to remove the effects of scratches on the cut surface. Paper sequentially 800#→1500#→
After polishing with 2000#, the edges were rounded and finished using the three-point bending method using an Instron universal testing machine. The bending strength (transverse rupture strength) is determined by the following formula. Transverse rupture strength = 3/2 Pm/d ₂ w where Pm: Maximum breaking load (Kg); Distance between supporting points (cm) d: Thickness of the sample (cm) w: Width of the sample (cm). Data of Examples of the present invention are shown in Tables 1 to 4 together with Reference Examples.

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[Table] Figure 1 shows 4 mol% of Pb(Y1/2Nb1/2)O ₃
Additives Sb ₂ O ₃ , In ₂ O ₃ , MgO
The sintered densities of the samples of Examples 4, 16, and 19 in which the additive was added are shown together with those of the samples of Reference Examples 8, 7, and 9 in which no additive was added. While the sintered density of additive-free materials is less than 7.5, Sb ₂ O ₃ , In ₂ O ₃ ,
It is clear that in the examples in which MgO was added, the sintered density was improved to 7.6 to 7.7. FIG. 2 shows the coupling coefficient KP for the same sample as in FIG. In the composition without additives, KP is about 60%, but by adding Sb ₂ O ₃ , MgO, and Ta ₂ O ₅ , KP is improved by 5 to 7%. FIG. 3 again shows the bending strength of the same sample as in FIG. The bending strength of additive-free material is 5×10 ² Kg/
cm ² , whereas in the material of this example, the sintered density is improved due to the effect of additives, and the bending strength is 10 × 10 ² Kg.
It is clear that the mechanical strength is improved. For this reason, cracks and chips during processing of thin plate ceramic resonators of around 100 μm are reduced, and retention can be significantly improved. FIG. 4 shows the relationship between the amounts of the additives Sb ₂ O ₃ and MgO and the bending strength, and it can be seen that the samples of Examples have a large bending strength. By the way, using the material of Example 19 of the present invention and the material of Reference Example 9 which does not contain additives, a 30mmφ×200μ
When manufacturing 1,000 disc resonators of m size, the yield up to the final process is 95% for the former, while for the latter.
It was 75%. In the case of the reference example, the final yield was low due to many cracks and chips during the manufacturing process due to insufficient mechanical strength when made into a thin plate, whereas in the case of the example, a high yield was obtained. As is clear from the above examples and reference examples,
While the oxide piezoelectric material according to the present invention has excellent piezoelectric properties, its mechanical strength is improved compared to conventional products, so it can be easily processed into thin sheets of, for example, around 100 μm, and has many practical advantages. It can be said that it is a thing.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the sintered densities of Examples and Reference Examples;
FIG. 2 is a diagram similarly showing the coupling coefficient, FIG. 3 is a diagram similarly showing the bending strength, and FIG. 4 is a diagram showing the relationship between the amount of additive added and the bending strength.

Claims (1)

[Claims] 1 Basic composition is PbTiO ₃ 40.0 to 50.0 mol%,
_PbZrO3 45-59.5 mol% and Pb(Y1/2Nb1/
2) A solid solution consisting of 0.5 to 5.0 moles of O ₃ , in which a portion of Pb in the composition is replaced with 10 mol % or less of one or a combination of two or more of Br, Sr, and Ca, and In ₂ An oxide piezoelectric material comprising 0.1 to 1.0% by weight of at least one selected from O ₃ , MgO, and Sb ₂ O ₃ .