KR100544091B1 - Piezoelectric Ceramic Composition - Google Patents

Abstract

The present invention relates to a piezoelectric ceramic composition having a large electromechanical coupling coefficient, high mechanical quality coefficient, and sintering at low temperature, and having useful properties as a material for piezoelectric parts, and more particularly, to formula (1-xy) Pb (Zr _{1). -a} , Ti _a ) O ₃ -xPb (Mn _1/3 Nb _2/3 ) O ₃ -yPb (Cu _1/3 Nb _2/3 ) O ₃ , In the above formula, x, y and a are piezoelectric ceramic compositions, wherein 0 <x≤.08, 0 <y≤0.1, and 0.4≤a≤0.6, respectively.

The piezoelectric ceramic composition according to the present invention has a high mechanical quality factor and a large electromechanical coupling coefficient, so that the heat generation is small when driving, the electrical and mechanical loss is low, and there is almost no deterioration even in long time use.

Piezoelectric ceramic

Description

Piezoelectric Ceramic Composition {A PIEZO CERAMIC COMPOSITION}

1 is a graph showing the sintered density according to the sintering temperature of the piezoelectric ceramic composition according to the present invention,

2 is a graph showing the dielectric constant according to the sintering temperature of the piezoelectric ceramic composition according to the present invention,

3 is a graph showing the change of the electromechanical coupling coefficient according to the sintering temperature of the piezoelectric ceramic composition according to the present invention,

4 is a graph showing the change in the mechanical quality factor according to the sintering temperature of the piezoelectric ceramic composition according to the present invention,

5 is a flowchart illustrating a manufacturing process of a piezoelectric ceramic using the piezoelectric ceramic composition according to the present invention.

The present invention relates to a piezoelectric ceramic composition, and more particularly, to a piezoelectric ceramic composition having a large electromechanical coupling coefficient, a high mechanical quality coefficient, and sintering at low temperature, which have useful properties as a material for piezoelectric parts.

In general, piezoelectric phenomenon exists in a material having an asymmetric crystal structure. The name implies two meanings of pressure and electricity, and means an effect therebetween. When a force is applied to the piezoelectric body, electric charges are generated, which is called a piezoelectric effect. On the contrary, when electricity is applied, deformation occurs, which is called a reverse piezoelectric effect.

There are several materials exhibiting piezoelectric phenomena among ceramic materials, but the most important commercial material is Pb (Ti, Zr) O3 (hereinafter referred to as PZT) which exhibits large and stable piezoelectric phenomena.

The piezoelectric material is capable of mutual conversion of electrical energy and mechanical energy, and can be used as a transduce that can mutually convert these energies using this phenomenon.

Piezoelectric ceramics have a wide variety of applications, such as acoustic sensors, ultrasonic sensors, actuators, and the like.

In addition, the piezoelectric ceramic composition used to make a piezoelectric transformer or a vibrator for an ultrasonic cleaner has to have a high mechanical quality factor (Qm) because the material must have a low heat generation during driving, and an electromechanical coupling is required to obtain a high boost ratio. The coefficient of electromechanical coupling (K) must be large.

The electromechanical coefficient K and the mechanical quality factor Q _m exhibiting the piezoelectric properties described above are defined as follows.

Electromechanical coupling factor (k)

The physical meaning of the electromechanical coupling coefficient (k) is the degree to which the percentage of the electrical energy is converted to mechanical energy when the electrical energy is applied to the piezoelectric (a form in which the remaining energy not converted as a conversion rate is returned without being consumed, Conversely, mechanical energy is converted into electrical energy by a few%). When one-way electrical energy is applied, the ratio converted to one-way mechanical energy is (K ₁₁ ) ² and three-way when one-way electric energy is applied. Mechanical energy conversion is represented by (K ₁₃ ) ² .

Thus, the electromechanical coupling coefficient is expressed as the square root of the energy conversion rate. For example, if K ₁₃ is 0.3, the concept is that electrical energy of about 9 is generated in three directions when 100 is applied in one direction.

On the other hand, the quality factor is the electrical quality factor (Q _e ) and the mechanical quality factor (Q _m ), Q _e is the inverse of the electrical loss (tan δ). Q _m, on the other hand, is the concentration of the displacement and the time difference response to the stress due to the mechanical vibration damping of the vibrating body. That is, it has a physical concept to the extent of minute parallax in which deformation appears when stress is applied.

In addition, in order to maximize the conversion efficiency of piezoelectric transformers, electrical and mechanical losses should be suppressed as much as possible, and reliability deterioration should be high because characteristic deterioration should be small even after long use.

Pb (Zr, Ti) O _{3, which} is a general piezoelectric material, causes volatilization of PbO at high sintering temperature (about 1200 ° C.) during sintering, and volatilization of PbO causes a problem of decreasing product uniformity.

That is, PZT used as a conventional piezoelectric material also has a mechanical quality factor It is about 500 and has a characteristic of K ₃₃ 0.45, which is insufficient for application to a piezoelectric transformer. In addition, due to the hassle of using the atmosphere powder during sintering is difficult to mass-produce, there is a disadvantage that the environmental pollution due to the volatilization of PbO.

It is an object of the present invention to provide a piezoelectric ceramic composition having suitable properties as a piezoelectric part material, which is sinterable at low temperatures of 1000 to 1050 ° C., has little loss of electrical and mechanical properties, and exhibits a high reliability index in long time use.

In addition, an object of the present invention is to provide a piezoelectric ceramic composition having excellent electromechanical coupling coefficient and mechanical quality coefficient because it can be mass produced by sintering at low temperature to prevent volatilization of PbO.

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Hereinafter, the present invention will be described in detail.
That is, in the piezoelectric ceramic comprising a compound such as Pb, Zr, Mn, Ti, Nb, etc. as a base composition, (1-xy) Pb (Zr _1-a , Ti _a ) O ₃ -xPb (Mn _{1 / In} the formula represented by ₃ Nb _2/3 ) O ₃ -yPb (Cu _1/3 Nb _2/3 ) O ₃ , x, y and a are each 0 <x≤0.08, 0 <y≤0.1, 0.4≤a≤ 0.6, and as a low-temperature sintering additive, (1-z) BaO-zCuO oxide is contained in an amount of 5% by weight based on the total weight of the composition, wherein z is 0.5≤z≤0.9, and (1-z) BaO is It is obtained by selecting from the compound BaO or BaCO ₃ , the zCuO is obtained by selecting from the compound CuO or Cu ₂ O.

Accordingly, the piezoelectric ceramic composition of the present invention is prepared by mixing PbO, ZrO ₂ , TiO ₂ , MnCO ₃ , CuO, Nb ₂ O ₅ in accordance with an arbitrarily determined composition ratio.

The piezoelectric ceramic composition of the present invention is represented by the following formula.

[Formula 1]

(1-xy) Pb (Zr _1-a , Ti _a ) O ₃ -xPb (Mn _1/3 Nb _2/3 ) O ₃ -yPb (Cu _1/3 Nb _2/3 ) O ₃

In the above formula, x, y and a are 0 <x ≦ 0.08, 0 <y ≦ 0.1 and 0.4 ≦ a ≦ 0.6, respectively.

When the composition of the piezoelectric ceramic according to the present invention is out of the above range, the electrical piezoelectric properties such as the electromechanical coupling coefficient (K) or the mechanical quality factor (Q) are degraded or the sintering temperature is raised to 1000 ° C. or more, thereby the piezoelectric component It is difficult to expect the effect as a material.

According to the present invention, PbO, ZrO ₂ , TiO ₂ , MnCO ₃ , and Nb ₂ O ₅ are weighed based on the total amount of the composition according to the desired composition ratio, and the scales are scaled to the second decimal place by electronic scale. After precisely taking and mixing, the additive (1-z) BaO-zCuO oxide is added thereto so as to be sintered at low temperature, followed by mixing and drying.

In the present invention, (1-z) BaO-zCuO oxide (hereinafter referred to as BC) is added as a low-temperature sintering additive for low-temperature sintering; In the above formula, z is 0.5 ≦ z ≦ 0.9, (1-z) BaO is obtained by selecting from compound BaO or BaCO ₃ , and zCuO is obtained by selecting from compound CuO or Cu ₂ O.

The low temperature sintering additive BC is preferably added in an amount of 5% by weight or less based on the total weight of the composition, and BC serves to maintain low temperature sintering without significantly lowering the piezoelectric properties of the ceramic composition before addition. When BC is added 5% by weight or more, the sintering temperature can be lowered, but the K and Q values, which are piezoelectric properties of the piezoelectric ceramic, are also lowered simultaneously.

1 of the accompanying drawings, the composition ratio of the piezoelectric ceramic composition according to the present invention is 0.92Pb (Zr _.5 , Ti _.5 ) O ₃ -0.048Pb (Mn _1/3 Nb _2/3 ) O ₃ -0.032Pb (Cu _The sintered density with sintering temperature change was shown as _1/3 Nb _2/3 ) O ₃ , and a satisfactory sintered density was obtained in the low temperature range of 1000 to 1100 ° C.

Figure 2 shows that the dielectric constant according to the sintering temperature of the piezoelectric ceramic composition according to the composition formula is in the range of about 1000 to 1150, the composition is in the dielectric constant desirable as a piezoelectric material.

In addition, it can be seen in FIG. 3 that the piezoelectric electromechanical coefficient of the composition according to the composition formula has a high value of 0.55 or more, and FIG. 4 shows that the Q value is 2000 or more regardless of the sintering temperature. .

5 briefly illustrates a manufacturing process of the piezoelectric ceramic using the piezoelectric ceramic composition according to the present invention.

Hereinafter, the present invention will be described in more detail with reference to the following Examples. However, the following examples are set forth to illustrate the invention and the variables of each manufacturing step, such as temperature, time, pressure, binder amount, etc., are arbitrarily changed within the scope of the invention by those skilled in the art. Can be. Therefore, the present invention is not limited by the following examples.

EXAMPLES Preparation of Piezoelectric Ceramics

The composition formula of _{0.92Pb (Zr .5, Ti .5)} O 3 - 0.048Pb (Mn 1/3 Nb 2/3) O 3 - 0.032Pb to a _{(Cu 1/3 Nb 2/3) O 3} PbO, ZrO ₂ , TiO ₂ , MnCO ₃ , Nb ₂ O _5, CuO were calculated as PbO: ZrO ₂ : TiO ₂ : MnCO ₃ : Nb ₂ O ₅ : CuO = 1: 0.46: 0.46: 0.016: 0.053: 0.0106 in molar ratio, The total amount of the mixture was 100 g, and the relative amount was determined as PbO: ZrO ₂ : TiO ₂ : MnCO ₃ : Nb ₂ O ₅ : CuO = 66.93: 17.0: 11.02: 0.55: 4.25: 0.25.

According to the determined amount, PbO, ZrO ₂ , TiO ₂ , MnCO ₃ , Nb ₂ O ₅ are precisely taken up to a few milligrams of decimal places with an electronic balance, and then, additive BC is added thereto to allow sintering at low temperature. After the mixing and drying of each component is carried out.

Then, the mixed and dried mixed powders were calcined at 850 ° C. for 3 hours through the mixing step of each component. The temperature increase rate was 5 ℃ per minute and an alumina crucible was used. After the calcination step is pulverized finely by alumina-induced grinding to perform a grinding mill with a ZrO ₂ ball with a diameter of 1 mm for regrinding.

Then, the powder regrind through the grinding step is dried in a drier, 10% by weight of 10% PVA aqueous solution is added as a binder, and then sieved through a 100 mesh sieve to granulate.

Then, after performing the granulation step, a cylindrical mold having an inner diameter of 10 mm was molded into a disk shape having a thickness of about 1 mm, and a molding step was performed by applying a pressure of 1 ton by a hydraulic press during molding.

In order to remove the binder of the molded product through the molding step, a binder removal step is performed for 12 hours at 500 ° C. by raising the temperature to 2.5 ° C./minute per hour.

Finally, the sintering step was carried out in the furnace, and no powder for controlling the atmosphere was used. At this time, in order to prevent the adhesion between the specimens were sprayed in between. The rate of temperature increase was 2.5 ° C. per minute, and was maintained for 2 hours at 50 ° C. at 900-1050 ° C. sintering temperature.

In addition, the external electrode was first screen-printed Ag silver electrode through the external electrode coating and silver sintering step, and the silver sintered part was cooled to room temperature after maintaining at 650 ° C for 10 minutes.

Finally, through the polarization step, the polarization was applied to both terminals and maintained for 15 minutes in the range of 120 to 130 ° C. at a voltage of 2 to 3 KV / mm.

According to the present invention, it is possible to produce a piezoelectric ceramic composition having a high mechanical quality factor, a large electromechanical coupling factor, and sintering at a low temperature of 1000 to 1050 ° C.

The piezoelectric ceramic composition according to the present invention has a high mechanical quality factor and a large electromechanical coupling coefficient, so that the heat generation is small when driving, the electrical and mechanical loss is low, and there is almost no deterioration even in long time use.

Claims (2)

In a piezoelectric ceramic comprising a compound such as Pb, Zr, Mn, Ti, Nb, etc. as a base composition, In the formula represented by (1-xy) Pb (Zr _1-a , Ti _a ) O ₃ -xPb (Mn _1/3 Nb _2/3 ) O ₃ -yPb (Cu _1/3 Nb _2/3 ) O ₃ x, y and a are each 0 <x ≦ 0.08, 0 <y ≦ 0.1, 0.4 ≦ a ≦ 0.6. The method of claim 1, As a low-temperature sintering additive, (1-z) BaO-zCuO oxide is contained in an amount of 5% by weight based on the total weight of the composition, wherein z is 0.5≤z≤0.9, and (1-z) BaO is a compound BaO or BaCO _{It is} obtained by selecting from ₃ , the zCuO is obtained by selecting from the compound CuO or Cu ₂ O piezoelectric ceramic composition.

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