KR101681386B1 - Lead-free piezoelectric ceramic composition and Preparation method thereof - Google Patents

Abstract

The present invention relates to a lead-free piezoelectric ceramic composition and a method of manufacturing the same. INDUSTRIAL APPLICABILITY The lead-free piezoelectric ceramics composition according to the present invention is not only environmentally friendly but also contains no lead, and has a high density with a relaxed ferroelectric material having a uniform particle size and narrow particle size distribution as a medium, Structure, which is excellent in electric field organic characteristics. In addition, since it is manufactured through a high energy ball-milling treatment, it is advantageous that process time and process temperature are easily controlled, thereby improving process efficiency and process cost.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a lead-free piezoelectric ceramic composition and a preparation method thereof,

The present invention relates to a lead-free piezoelectric ceramic composition and a manufacturing method thereof, and more particularly, to a lead-free piezoelectric ceramic composition having a structure in which bismuth (Bi) based ferroelectric particles are dispersed in a bismuth Sintering property and electric field organic performance, and a method for manufacturing the same.

In piezoelectric ceramics, Pb (Zr, Ti) O ₃ (hereinafter referred to as "PZT") ceramic material has been used in many applications because of its excellent piezoelectric properties, low cost, and well-known manufacturing process. However, since the material contains lead as a main component, it is not only harmful to human body but also causes environmental pollution, and there is a growing need for lead-free materials that can replace such materials.

Until now, studies on the non-bonded piezoelectric ceramics have been actively conducted on a bismuth (Bi) based leadless ceramic having Bi (Na, K) TiO ₃ composition and a niobium (Nb) based leadless ceramic having a (K, Na) NbO ₃ composition .

For example, Patent Document 1 discloses a bismuth composite perovskite lead-free piezoelectric ceramics having improved dielectric loss characteristics and a manufacturing method thereof, and Patent Document 2 discloses a method of manufacturing a (K _{1 - x} Na _x ) Discloses a lead-free piezoelectric ceramic composition having KCuTaO and CuO added to a ceramic composition having a composition of NbO ₃ and having excellent mechanical quality factor.

However, since the sintering is performed at a high temperature of 1200 ° C or more for densification of the piezoelectric material, volatile elements such as Na and K may be volatilized. To prevent this, excessive Na and K raw material powders are used, The sintering temperature must be limited, and the characteristics of the piezoelectric ceramics accordingly deteriorate.

Therefore, it is required to develop lead-free ceramics having high density at low temperature and high sintering at the time of sintering because sintering performance is improved as well as conventional PZT piezoelectric materials can be substituted by excellent piezoelectric properties.

Korean Patent No. 10-1268487 Korean Patent No. 10-1310450

An object of the present invention is to provide a lead-free piezoelectric ceramic composition having excellent piezoelectric characteristics and improved sinterability and having high density even at a low sintering temperature.

Another object of the present invention is to provide a method of manufacturing the PFC ceramic composition.

Still another object of the present invention is to provide a piezoelectric application device comprising the Pb-free piezoelectric ceramic composition.

In order to achieve the above object,

The present invention, in one embodiment,

(Bi) -based ferroelectric material is dispersed in a bismuth (Bi) -based ferroelectric material as a medium,

The bismuth (Bi) -based relaxed ferroelectric material has an average particle size of 1 to 50 占 퐉 and has a particle size distribution satisfying the following expression (1) in a particle size range of 1 to 100 占 퐉:

[Equation 1]

ΔDP ≤ 70 μm

In Equation (1) above,

And? DP represents a deviation between the maximum grain size and the minimum grain size in the region where the frequency of the bismuth (Bi) -semiconductor relaxation ferroelectric is 90% or more.

Further, in another embodiment of the present invention,

Performing high energy ball milling of a bismuth (Bi) based relaxation ferroelectric material represented by the following formula (1); And

There is provided a method of manufacturing a lead-free piezoelectric ceramic composition including a step of mixing and molding a milled bismuth (Bi) -based relaxed ferroelectric and a bismuth (Bi) -based ferroelectric material:

[Chemical Formula 1]

_{(1-x) [Bi 1} /2 (Na (1-y) K y) 1/2 TiO 3] -xLaFeO 3

In Formula 1,

x is 0.018 to 0.035; And

y is 0.16-0.25.

Furthermore, the present invention, in another embodiment,

A piezoelectric body manufactured using the lead-free piezoelectric ceramic composition; And

And at least a pair of electrodes supported in contact with the piezoelectric body.

INDUSTRIAL APPLICABILITY The lead-free piezoelectric ceramics composition according to the present invention is environmentally friendly since it does not contain lead, has high density and excellent electric field organic characteristics even at a low sintering temperature. In addition, since it is manufactured through a high energy ball-milling treatment, it is advantageous that process time and process temperature are easily controlled, thereby improving process efficiency and process cost.

FIG. 1 is a graph showing the particle size distribution of a bismuth-based relaxation type ferroelectric substance according to a high-energy ball milling treatment time in one embodiment.
2 is a graph showing the firing shrinkage ratio for each high-energy ball milling treatment time according to the firing temperature of the ferroelectric of the bismuth-based relaxation type in another embodiment.
Fig. 3 is a graph showing the strain history by high energy ball milling treatment time according to the applied electric field of the lead-free piezoelectric ceramics composition in another embodiment.
4 is a graph showing the normalized strain (S _max / E _max ) according to the high energy ball milling treatment time of the lead-free piezoelectric ceramics composition in one embodiment.

While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail.

It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

In the present invention, the terms "comprising" or "having ", and the like, specify that the presence of a feature, a number, a step, an operation, an element, a component, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.

Hereinafter, the present invention will be described in detail with reference to the drawings, and the same or corresponding components are denoted by the same reference numerals regardless of the reference numerals, and a duplicate description thereof will be omitted.

In the present invention, the term "unimodal distribution" refers to a particle size distribution graph in which the particle size is expressed as a function of 10 ^x . When the range of x is 0 to 2, Means the particle size distribution in which the average fraction with respect to the particle size value appears in the form of a single peak. For example, as in Production Example 4 of Fig. 1, an average fraction of 30 or more continuous arbitrary particle size values having a constant particle size in the range of x = 0 to 2, that is, a particle size of 1 to 100 m When it appears in the form of a single peak, it is said to have a "unipolar distribution".

In the present invention, "bimodal distribution" refers to a particle size distribution graph in which the particle size is expressed as a function of 10 ^x . When the range of x is 0 to 2, Means the particle size distribution in which the average fraction with respect to the particle size value appears in the form of two peaks. For example, as in Production Example 2 of Fig. 1, the average fraction of 30 or more arbitrary particle size values having a constant particle size interval in a range of x = 0 to 2, that is, a particle size of 1 to 100 m When two peaks appear in superimposed form, it is said to have a "bimodal distribution".

The present invention relates to a lead-free piezoelectric ceramic composition and a method of manufacturing the same.

Until now, various studies have been actively conducted on non-bonded piezoelectric ceramics such as a bismuth-based lead-free ceramic having a composition of Bi (Na, K) TiO _{3 and} a niobium-based leadless ceramic having a (K, Na) NbO ₃ composition. However, since piezoelectric materials developed to date have been sintered at a high temperature of 1200 ° C or higher in order to densify the material, volatile elements such as Na and K may be volatilized. In order to prevent this, excessive amounts of Na and K raw material powders must be used, or the sintering temperature must be limited, so that the characteristics of the piezoelectric ceramics accordingly deteriorate.

Accordingly, the present invention relates to a lead-free piezoelectric ceramic composition having a structure in which bismuth (Bi) -based ferroelectric particles are dispersed in a bismuth (Bi) -based relaxed ferroelectric substance and sinterability and field organic performance are improved by using a high energy ball milling method, Method.

INDUSTRIAL APPLICABILITY The lead-free piezoelectric ceramics composition according to the present invention is not only environmentally friendly but also has high density at a low sintering temperature by using a bismuth (Bi) based relaxation ferroelectric material having a uniform particle size and narrow particle size distribution as a medium . In addition, it has a structure in which bismuth (Bi) -based ferroelectric particles are dispersed in the medium and is excellent in electric field organic characteristics. Further, since the process is manufactured through a high energy ball-milling process, it is easy to control process time and process temperature, thereby improving process efficiency and process cost.

Hereinafter, the present invention will be described in detail.

The present invention, in one embodiment,

(Bi) -based ferroelectric material is dispersed in a bismuth (Bi) -based ferroelectric material as a medium,

The bismuth (Bi) -based relaxed ferroelectric material has an average particle size of 1 to 50 占 퐉 and has a particle size distribution satisfying the following expression (1) in a particle size range of 1 to 100 占 퐉:

[Equation 1]

ΔDP ≤ 70 μm

In Equation (1) above,

And? DP represents a deviation between the maximum grain size and the minimum grain size in the region where the frequency of the bismuth (Bi) -semiconductor relaxation ferroelectric is 90% or more.

Specifically, the deviation between the maximum particle size and the minimum particle size may be 70 μm or less, 60 μm or less, or 50 μm or less.

The lead-free piezoelectric ceramic composition according to the present invention is a ferroelectric material having a bismuth-based relaxation type ferroelectric (hereinafter referred to as "relaxation type ferroelectric") having a perovskite structure as a medium and a bismuth ferroelectric ) May be dispersed. In general, a non-bonded piezoelectric material has a low electric field strain at a low electric field. However, the lead-free piezoelectric ceramics composition according to the present invention has a structure in which a ferroelectric is dispersed in a relaxed ferroelectric substance, so that it can have an excellent field organic performance even in a low electric field. More specifically, when a low electric field is applied to the lead-free piezoelectric ceramic composition according to the present invention, the ferroelectric dispersed in the relaxed ferroelectric induces the relaxed ferroelectric to be in phase transition to the ferroelectric, so that it can have a high electric field organic strain.

Here, the relaxed ferroelectric may be a compound represented by the following formula (1) having a perovskite structure, and may have an average particle size of 1 to 50 m:

[Chemical Formula 1]

_{(1-x) [Bi 1} /2 (Na (1-y) K y) 1/2 TiO 3] -xLaFeO 3

In Formula 1,

x is 0.018 to 0.035; And

y is 0.16-0.25.

More specifically, the average size of the relaxed ferroelectric is 1 to 45 m; 1 to 40 [mu] m; 1 to 30 [mu] m; 1 to 20 m; Or 1 to 10 [mu] m.

The particle size distribution of the relaxed ferroelectric may satisfy the following condition (1) in a particle size range of 1 to 100 μm, and may have a unimodal particle size distribution:

[Equation 1]

ΔDP ≤ 70 μm

In Equation (1) above,

? DP represents the deviation between the maximum grain size and the minimum grain size in the region where the frequency of the relaxation ferroelectric is 90% or more.

Specifically, in one embodiment, the grain sizes of three relaxation type ferroelectrics included in the Pb-free piezoelectric ceramics composition according to the present invention were analyzed. As a result, the three relaxed ferroelectrics were found to have an average grain size of about 1 to 50 μm. In addition, the region where the frequency of the relaxation type ferroelectric substance is 90% or more has a particle size range of about 1 to 60 μm, and the maximum particle size and minimum particle size variation (ΔDP) in the region are about 39 μm, 30 μm, and 7 μm Respectively. In addition, the particle size distribution of the relaxed ferroelectrics has a unimodal distribution in the particle size range of 1 to 100 μm. From these results, it can be seen that the grain size of the relaxed ferroelectric is small, uniform, and satisfies the condition of Equation (1) (see Experimental Example 1 and Fig. 1).

Further, the lead-free piezoelectric ceramics composition according to the present invention improves the sintering property and the plastic density, that is, the compactness is increased and the field organic performance is improved even at a low sintering temperature by controlling the grain size of the relaxed ferroelectric medium, .

As one example, the lead-free piezoelectric ceramic composition according to the present invention may have a normalization strain of 450 pm / V or more at an electric field of 4 kV / mm and may satisfy the following condition:

&Quot; (2) "

(S _max / E _max ) _uni / (S _max / E _max ) _bi ≥ 1.1

In Equation (2)

(S _max / E _max ) _uni represents a normalization strain of a lead-free piezoelectric ceramic composition including a relaxed ferroelectric having a unimodal particle size distribution in the range of 1 to 100 μm,

(S _max / E _max ) _bi represents a normalized strain of a lead-free piezoelectric ceramic composition including a relaxed ferroelectric having a bimodal particle size distribution in the range of 1 to 100 μm.

The lead-free piezoelectric ceramic composition according to the present invention has excellent electric field organic performance and satisfies the condition of Equation (2) 1.1 times or more; 1.15 times or more; 1.18 times or more; 1.2 times or more; Or 1.21 times or more.

Specifically, in one embodiment, the electric field organic strain of four kinds of the lead-free piezoelectric ceramics composition according to the present invention was measured. As a result, four types of lead-free piezoelectric ceramic compositions including a relaxed ferroelectric material having a unimodal particle size distribution in the range of 1 to 100 μm were obtained at about 523 pm / V, 517 pm / V, 542 pm / V and a normalization strain of 524 pm / V. In the case of a lead-free piezoelectric ceramic composition containing a relaxed ferroelectric material having a bimodal particle size distribution in the range of 1 to 100 mu m as a medium, it was found to have a normalized strain of about 422 pm / V. That is, when the lead-free piezoelectric ceramics composition contains a relaxed ferroelectric having a unimodal particle size distribution in the range of 1 to 100 μm, it is preferable to use a relaxed ferroelectric having a bimodal particle size distribution, It is found that the normalized strain is about 1.23 to 1.28 times higher.

From these results, it can be seen that the Pb-free piezoelectric ceramics composition according to the present invention has improved electric field organic performance and satisfies the condition of Equation (2) (see Experimental Example 2).

Meanwhile, in the lead-free piezoelectric ceramic composition according to the present invention, the ferroelectric may be a compound represented by the following formula (2)

(2)

_{Bi 1/2 (Na (1} -z) K z) 1/2 TiO 3

In Formula 2,

z is 0.16-0.22.

The content of the ferroelectric may be 5 to 55 parts by weight based on 100 parts by weight of the relaxation type ferroelectric. Specifically, the content is 5 to 50 parts by weight; 5 to 40 parts by weight; 5 to 30 parts by weight; Or 5 to 20 parts by weight.

The lead-free piezoelectric ceramic composition according to the present invention can prevent the decrease in the low-temperature deformation or the maximum strain in the high-electric field by including the ferroelectric within the above range, and maximize the field organic strain in the low driving electric field.

In addition, the present invention may be embodied as one embodiment,

Performing high energy ball milling of a bismuth (Bi) based relaxation ferroelectric material represented by the following formula (1); And

There is provided a method of manufacturing a lead-free piezoelectric ceramic composition including a step of mixing and molding a milled bismuth (Bi) -based relaxed ferroelectric and a bismuth (Bi) -based ferroelectric material:

[Chemical Formula 1]

_{(1-x) [Bi 1} /2 (Na (1-y) K y) 1/2 TiO 3] -xLaFeO 3

In Formula 1,

x is 0.018 to 0.035; And

y is 0.16-0.25.

The manufacturing method of a lead-free piezoelectric ceramic composition according to the present invention is characterized in that before manufacturing a mixture in which a ferroelectric is dispersed in a relaxation type ferroelectric represented by the general formula (1), a high-energy ball milling of a relaxed ferroelectric, There is an advantage that the sinterability and the electric field organic performance of the composition can be improved.

Hereinafter, the above manufacturing method will be described in more detail in each step.

First, in the step of performing high energy ball milling of the relaxation type ferroelectric material represented by the following formula 1, the relaxation type ferroelectric and the solvent, which are the medium, are charged into a milling vessel together with the milling balls, followed by pulverization with high mechanical energy, Lowering the grain size of the ferroelectric and making it uniform:

[Chemical Formula 1]

_{(1-x) [Bi 1} /2 (Na (1-y) K y) 1/2 TiO 3] -xLaFeO 3

In Formula 1,

x is 0.018 to 0.035; And

y is 0.16-0.25.

Here, the high energy ball milling can be performed by a high energy ball milling apparatus composed of a milling vessel and a milling ball, and the high energy ball milling apparatus is not particularly limited as long as it is commonly used in the art Can be used. For example, the high energy ball mill apparatus may include a vibratory / shaker mill, a planetary mill, an attrition mill, and the like.

The milling balls function to apply mechanical energy to the relaxation type ferroelectric material during high energy ball milling, and can be selectively used among zirconia series, iron series and tungsten carbide series. In addition, the milling balls can be charged into the milling vessel in the milling vessel at the time of high energy ball milling, and the total weight of the milling balls to be charged is 2 to 5 parts by weight per 1 part by weight of the relaxation type ferroelectric, 2 to 4 parts by weight; 3 to 4 parts by weight; Or 2.5 to 3.5 parts by weight.

For example, when performing wet high energy ball milling, the relaxed ferroelectric, milling balls and solvent may be charged into the milling vessel at a weight ratio of 1: 2 to 5: 2 to 5, but are not limited thereto.

The present invention can prevent the yield sensitivity of the milled relaxed ferroelectric material by controlling the weight of the milling balls in the above range during the high energy ball milling and also can reduce mechanical energy such as impact energy generated by the milling balls It is possible to effectively control the dispersion and pulverization of the relaxed ferroelectric.

Further, the execution time of the high-energy ball milling may be 10 to 100 minutes, specifically 10 to 90 minutes; 10 to 80 minutes; 10 to 70 minutes; Or 15 to 65 minutes.

In addition, the rotation speed of the high energy ball milling may be 700 to 1100 rpm, specifically 700 to 1050 rpm; 700 to 1000 rpm; To 700 to 950 rpm; Or 750 to 1000 rpm.

The present invention has an advantage in that the particle size of the relaxation ferroelectric can be controlled with minimum time and cost by controlling the execution time and the rotation speed of high energy ball milling within the above range.

The method of manufacturing a lead-free piezoelectric ceramics composition according to the present invention is a method of manufacturing a lead-free piezoelectric ceramic composition by controlling a particle size by performing high energy ball milling of a relaxed ferroelectric medium as a medium prior to preparing a mixture of a relaxed ferroelectric and a ferroelectric material, A lead-free piezoelectric ceramic composition having a compactness can be produced.

As one example, the milled relaxation type ferroelectric can satisfy the following condition (3): " (3) "

&Quot; (3) "

(SH _30m - SH _0m ) / SH _0m ? 0.15

In Equation (3)

The SH _{30 m} represents the firing shrinkage at 1100 ° C of the relaxed ferroelectric material subjected to the high energy ball milling for 30 minutes,

SH _0m represents the firing shrinkage at 1100 ° C of the relaxed ferroelectric material subjected to high energy ball milling for 0 minutes.

Specifically, the milled relaxation type ferroelectric has improved firing shrinkage ratio, satisfying the condition of the formula (3) to 0.16 or more; 0.17 or more; 0.18 or more; 0.19 or more; Or 0.20 or more.

In one embodiment, the firing shrinkage of the relaxed ferroelectric material subjected to the high energy milling for 30 minutes and the relaxed ferroelectric material not subjected to the high energy milling treatment (treatment time: 0 minutes) was measured. As a result, the relaxed ferroelectric material subjected to the high energy milling for 30 minutes had a shrinkage ratio of about 11.8%, while the relaxed ferroelectric material without the high energy ball milling had a shrinkage ratio of about 9.0%. That is, the relaxation type ferroelectric with high energy ball milling is small and uniform in grain size, and the plastic shrinkage ratio is improved by about 2.1% as compared with the relaxation type ferroelectric without high-energy ball milling. (See Experimental Example 1).

On the other hand, in the relaxed ferroelectric,

Bi ₂ O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ and TiO ₂ , La ₂ O ₅ and Fe ₂ O ₅ are respectively weighed and wet-mixed and pulverized; And

And calcining the ground mixture.

Specifically, the relaxed ferroelectric material is obtained by weighing and mixing Bi ₂ O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , TiO ₂ , La ₂ O ₅ and Fe ₂ O ₅ according to the composition of the formula (1) By calcining at about 750 to 950 캜 for 1 to 3 hours to perform a solid phase chemical reaction.

Since the Na ₂ CO ₃ and K ₂ CO ₃ have hygroscopicity, they may absorb moisture from the surrounding environment during storage and may increase the weight. If the drying is not sufficient before weighing, The piezoelectric characteristics may be changed accordingly. Therefore, when Na ₂ CO ₃ and K ₂ CO ₃ powder are sufficiently dried in a drying oven at 80 to 100 ° C for 20 to 28 hours, there is no further weight loss due to drying of the moisture already contained, that is, After checking the condition, weighing can be done.

In addition, the pulverization can be used without any particular limitation as long as it is a method or condition conventionally used in the art. For example, the pulverization may be performed by a ball milling method. When the pulverization is performed by a ball milling method, wet milling may be performed using an organic solvent such as anhydrous ethanol, ethanol, or acetone for 24 hours.

Furthermore, the method of manufacturing the relaxed ferroelectric may further include drying the mixture at 80 to 90 DEG C before the step of calcining the ground mixture.

Next, the step of mixing and molding the milled relaxation ferroelectric and the ferroelectric is a step of preparing a mixture in which the ferroelectric is dispersed in the relaxed ferroelectric, and adding a binder to the mixture to be molded.

Specifically, the above step is a step of mixing a ferroelectric material having a small particle size, a uniform relaxation type ferroelectric material and a ferroelectric material to produce a lead-free piezoelectric ceramic composition having a structure in which ferroelectric particles are dispersed in a relaxed ferroelectric material, a binder such as polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyethylene glycol (PEG), or the like can be mixed and molded.

In this case, the ferroelectric may be a compound represented by the following general formula (2), and the amount of the ferroelectric compound is 5 to 55 parts by weight based on 100 parts by weight of the relaxed ferroelectric, specifically 5 to 50 parts by weight; 5 to 40 parts by weight; 5 to 30 parts by weight; Or 5 to 20 parts by weight.

(2)

_{Bi 1/2 (Na (1} -z) K z) 1/2 TiO 3

In Formula 2,

z is 0.16-0.22.

The Pb free ceramic composition according to the present invention can maximize the field organic strain at a low driving electric field by including the ferroelectric within the above range.

In addition, the method of manufacturing a lead-free piezoelectric ceramic composition according to the present invention may further include a step of sintering the molded product after the step of mixing and molding the relaxed ferroelectric and the ferroelectric.

In this manufacturing method, a lead-free piezoelectric ceramics composition can be produced by sintering a molded product obtained by molding a mixture of a relaxed ferroelectric and a ferroelectric with a binder. At this time, the sintering temperature is preferably such that the ferroelectric is dispersed in a relaxed ferroelectric medium It is not particularly limited as long as it does not occur.

As one example, it can be carried out at a temperature range of 950 to 1150 캜 for 1 to 5 hours, specifically at 950 to 1100 캜; 950 to 1075 C; Or from 950 to 1050 < 0 > C for 1 to 3 hours.

By controlling the sintering temperature within the above range, the present invention can sufficiently perform sintering between mixed raw materials and prevent sintering of the sintered body from being melted.

Further, the present invention, in one embodiment,

A piezoelectric body manufactured using a lead-free piezoelectric ceramic composition; And

And at least a pair of electrodes supported in contact with the piezoelectric body.

Here, the piezoelectric application device refers to a piezoelectric ceramic product including the piezoelectric ceramic composition of the present invention so as to exhibit piezoelectric characteristics of the piezoelectric application device.

The piezoelectric application device according to the present invention includes a piezoelectric body and a pair of electrodes for supporting the piezoelectric body. In this case, the piezoelectric body is not particularly limited in shape and size, and may be formed in accordance with the purpose of pressure measurement, And can be appropriately selected depending on the application of the device. Specifically, for example, when used as a purpose of pressure measurement, the piezoelectric body may be formed into a plate shape having a rectangular plane structure, a circular plane structure, etc., a plate shape having a central through hole in the thickness direction, a prismatic shape, It can be used in various shapes. Further, the piezoelectric application element may have a shape in which two or more piezoelectric bodies are laminated.

Further, in the piezoelectric application device according to the present invention, the pair of electrodes refers to a conductive layer formed on the surface of the piezoelectric body and held in contact with the surface of the piezoelectric body. One of the pair of electrodes may be formed on one surface of the piezoelectric body and the other may be formed on the other surface thereof; Or a pair of electrodes may be formed together on one surface of the piezoelectric body.

At this time, the shape, size, and material of the electrode are not particularly limited, and may be appropriately selected depending on the application of the piezoelectric application device and the like. Specifically, for example, the electrode may have a flat shape. When an electrode is formed on the same surface of the piezoelectric body, the electrode may have a comb-like or semicircular shape.

Further, the electrode forming process may be performed by a method commonly used in the art. More specifically, each of the electrodes can be formed by applying a conductive paste to a desired piezoelectric surface and baking the conductive paste, but the present invention is not limited thereto.

The piezoelectric application device according to the present invention is environmentally friendly using the lead-free piezoelectric ceramic composition according to the present invention, and has advantages of excellent denseness and electric field organic performance, so that it can be applied to various fields. Applicable fields can be applied from mobile phones, automobiles, TV displays, and so on, which are closely related to our lives, to the parts of various medical devices as well as filters, piezoelectric resonators, vibrators, sensors, actuators, transformers, Energy harvesting devices, and the like.

Hereinafter, the present invention will be described in more detail with reference to Examples and Experimental Examples.

However, the following Examples and Experimental Examples are merely illustrative of the present invention, and the present invention is not limited to the following Examples and Experimental Examples.

Manufacturing example  One. Bi _{0 .5} ( Na _{0 .82} K _{0 .18} ) _0.5 TiO ₃  Preparation of powder

The ferroelectric Bi _{0 .5} (Na _{0 .82} K _{0 .18} ) _0.5 TiO ₃ according to the present invention was prepared by a solid-state process. First, Bi ₂ O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ and TiO ₂ powders of the purity commonly used for industrial purposes having the same composition as Bi _{0 .5} (Na _{0 .82} K _{0 .18} ) _0.5 TiO ₃ Were each weighed and wet-mixed by ball milling for 24 hours using ethanol. The mixture in the form of dough was then dried at 80 to 90 DEG C and the dried mixture was calcined at about 850 DEG C for 2 hours to induce a solid phase reaction to prepare a ferroelectric powder.

Manufacturing example  2 - 6. 0.98 [ Bi _{0 .5} ( Na _{0 .78} K _{0 .22} ) _0.5 TiO ₃ ] -0.02 LaFeO ₃  Preparation of powder

0.98 [Bi _{0 .5} (Na _{0 .78} K _{0 .22} ) _0.5 TiO ₃ ] -0.02 LaFeO _3, which is a ferroelectric substance according to the present invention, was prepared by a solid-state process. First, Bi ₂ O ₃ , Na ₂ CO ₃ , K _{2 (} which is a purity of industrial use commonly used to have the same composition as that of 0.98 [Bi _{0 .5} (Na _{0 .78} K _{0 .22} ) _0.5 TiO ₃ ] -0.02 LaFeO ₃ Powders of CO ₃ , TiO ₂ , La ₂ O ₅ and Fe ₂ O ₅ were respectively weighed, wet-mixed by ball milling method using ethanol for 24 hours, and then the kneaded mixture was dried at 80 to 90 ° C . To that induced following the solid phase chemistry, by calcination for 2 hours, the mixture was dried at about _{850 ℃ 0.98 [Bi 0 .5 (} Na 0 .78 K 0 .22) 0.5 TiO 3] relaxation of -0.02LaFeO ₃ Type ferroelectric powders.

Then, the high energy ball milling of the relaxation type ferroelectric powders produced by using the above-formed ball milling equipment (Planetary Micro Mill pulverisette 7 premium line of FRISCH Co., Ltd.) was performed. At this time, the high-energy ball milling was carried out at a rotational speed of 800 rpm by charging a 80-mL vessel in such a manner that the ratio of the relaxed ferroelectric powder, zirconia balls and solvent was 1: 3: 4 by weight, The zirconia (ZrO ₂ ) balls had a radius of 3 mm, and the execution time was as shown in Table 1 below.

Run time Production Example 2 0 minutes Production Example 3 15 minutes Production Example 4 30 minutes Production Example 5 45 minutes Production Example 6 60 minutes

Example  1 - 20.

Prepared in Preparation Example _{1 Bi 0 .5 (Na 0 .82} K 0 .18) 0.5 TiO 3 ferroelectric powder as in Preparation Example 3 manufactured by _{6 0.98 [Bi 0 .5 (Na} 0 .78 K 0 .22 ) _0.5 TiO ₃ ] -0.02 LaFeO ₃ relaxation type ferroelectric powders were weighed at a weight ratio of 9: 1, respectively, ethanol was added, wet mixed by ball milling for 24 hours, and then dried. Thereafter, polyvinyl alcohol (PVA) was added so as to be added in an amount of 3 parts by weight based on the dried powder to form a mixture into a plate-like shape, and the mixture was sintered at a firing temperature shown in Table 2 for 2 hours to prepare a lead- .

Relaxed ferroelectric Ball milling processing time Firing temperature Example 1 In Production Example 3
Relaxed ferroelectric 15 minutes 950 ℃ Example 2 1000 ℃ Example 3 1050 ° C Example 4 1100 ℃ Example 5 1150 DEG C Example 6 In Production Example 4
Relaxed ferroelectric 30 minutes 950 ℃ Example 7 1000 ℃ Example 8 1050 ° C Example 9 1100 ℃ Example 10 1150 DEG C Example 11 In Production Example 5
Relaxed ferroelectric 45 minutes 950 ℃ Example 12 1000 ℃ Example 13 1050 ° C Example 14 1100 ℃ Example 15 1150 DEG C Example 16 Production Example 6
Relaxed ferroelectric 60 minutes 950 ℃ Example 17 1000 ℃ Example 18 1050 ° C Example 19 1100 ℃ Example 20 1150 DEG C

Comparative Example  1 - 3.

Prepared in Preparation Example _{1 Bi 0 .5 (Na 0 .82} K 0 .18) 0.5 TiO 3 prepared in Preparation Example as the ferroelectric _{2 0.98 [Bi 0 .5 (Na} 0 .78 K 0 .22) 0.5 TiO ₃ ] -0.02 LaFeO ₃ relaxed ferroelectric was weighed at a weight ratio of 9: 1, and ethanol was added thereto, wet mixed by a milling method for 24 hours, and then dried. Thereafter, polyvinyl alcohol (PVA) was added so as to be added in an amount of 3 parts by weight to the dried powder to form a mixture into a plate-like shape, and then sintered at a firing temperature shown in Table 3 for 2 hours to prepare a lead- .

Relaxed ferroelectric Ball milling processing time Firing temperature Comparative Example 1 In Production Example 2
Relaxed ferroelectric 0 minutes 1100 ℃ Comparative Example 2 1150 DEG C Comparative Example 3 1200 ℃

Experimental Example  1. Evaluation of compactness of Pb-free piezoelectric ceramics

In order to evaluate the compactness of the lead-free piezoelectric ceramic composition according to the present invention, the particle size distribution and the plastic shrinkage ratio of the relaxed ferroelectric powder used as the medium of the composition were measured according to the high energy ball milling time.

First, the particle size distribution of the relaxed ferroelectric materials of Preparation Examples 2 and 4 - 6 was measured and the measurement results are shown in Fig. Further, the relaxed ferroelectric powders prepared in Production Example 2-6 were calcined at 950 ° C, 1000 ° C, 1050 ° C, 1100 ° C, 1150 ° C and 1200 ° C for 2 hours, respectively, to determine the plastic shrinkage ratio with respect to the diameter of each relaxed ferroelectric Respectively. At this time, the firing shrinkage ratio was measured by measuring the particle diameters of the relaxed ferroelectric powder before and after firing, and the measured results are shown in FIG.

As shown in FIGS. 1 and 2, the lead-free piezoelectric ceramics composition according to the present invention has improved sinterability of the relaxed ferroelectric medium, which is excellent in the compactness.

Specifically, referring to FIG. 1, the relaxed ferroelectric material prepared in Production Example 4-6 was found to have an average grain size of about 1 to 50 μm after high-energy ball milling after sintering. In addition, it was confirmed that the region where the frequency of the relaxed ferroelectric substance was 90% or more had a particle size range of about 1 to 60 μm, and the deviation (ΔDP) between the maximum particle size and the minimum particle size existing in the region was about 50 μm. More specifically, the relaxation type ferroelectric materials prepared in Production Examples 9, 14, and 19 exhibited the maximum particle size and the minimum particle size deviation (? DP) in the above regions of about 39 μm, 30 μm, and 7 μm, respectively. In addition, the particle size distributions of the relaxed ferroelectrics were found to have a unimodal distribution in the particle size range of 1 to 100 μm.

On the other hand, it was confirmed that the relaxation type ferroelectric material produced in Production Example 2 had a deviation (? DP) of the maximum particle size and the minimum particle size in the region where the frequency of the relaxation type ferroelectric substance was 90% or more was about 85 占 퐉, And a bimodal distribution in the range.

This means that the grain size of the relaxed ferroelectric substance is large and uneven after sintering and the grain size distribution is wide, but it means that the grain size becomes smaller and homogeneous by the high energy ball milling, and the distribution becomes narrower.

In addition, as shown in FIG. 2, the relaxation type ferroelectric has a higher plastic shrinkage as the time for performing high energy ball milling at the same firing temperature is longer. Specifically, in the case of the firing temperature of 1100 ° C, the relaxation type ferroelectric of Production Example 2, in which the time of high energy ball milling was 0 minutes, exhibited a firing shrinkage of about 9.0%. On the other hand, the relaxation type ferroelectric materials of Production Example 3 to 6 in which the time of high energy ball milling was 15, 30, 45 and 60 minutes, respectively, showed plastic shrinkage rates of about 9.7%, 11.1%, 11.8% and 13.0%, respectively. This means that as the execution time of the high energy ball milling becomes longer, the grain size of the relaxed ferroelectric becomes small and uniform and the sinterability is improved.

From these results, it can be seen that the lead-free piezoelectric ceramics composition according to the present invention has improved sinterability of the composition by including a small-sized, uniform relaxation type ferroelectric material produced by high energy ball milling as a medium, .

Experimental Example  2. Normalization Strain Rate Evaluation

In order to evaluate the electric field induced deformation characteristics of the lead-free piezoelectric ceramic composition according to the present invention, the following procedure was performed.

First, the specimens prepared in Examples 4, 9, 14, 19 and Comparative Example 1 were processed to have a thickness of about 1.0 mm, cut to a thickness of about 1 mm, and then electrodes were formed on both surfaces of the specimen Respectively. At this time, the electrode was coated with a silver (Ag) electrode by a printing coating method and heat-treated at 650 to 750 ° C for 20 to 40 minutes to prepare an electrode.

An electric field of 0 to 5 kV / mm was applied to both surfaces of the prepared electrode, and a field organic hysteresis curve of the electrode was measured according to a high energy ball milling time using a linear variable differential transducer (LVDT) . In addition, the normalized strain (S _max / E _max ) was derived from the measured hysteresis curve, and the results are shown in FIGS. 3 and 4.

As shown in Figs. 3 and 4, the lead-free piezoelectric ceramic composition according to the present invention has excellent electric field organic deformation characteristics.

Specifically, referring to FIG. 3, all the electrodes manufactured using the specimens of Examples 4, 9, 14, 19 and Comparative Example 1 showed typical deformation characteristics of the piezoelectric material, . In addition, the maximum strain at 5 kv / mm electric field condition was found to be about 0.2% or less when the test piece of Comparative Example 1 was used. However, when the test pieces of Examples 4, 9, 14 and 19 were used, Respectively. This means that the specimens of the embodiment using the relaxed ferroelectric material in which the high energy ball milling is performed as the medium are improved in the compactness and the maximum strain (S _max ) is increased.

Further, referring to FIG. 4, the electrodes using the specimens of Examples 4, 9, 14 and 19 have normalized strains of about 523 pm / V, 517 pm / V, 542 pm / V and 524 pm / The electrode using the specimen of Comparative Example 1 was found to have a normalized strain of about 422 pm / V.

From these results, it can be seen that the lead-free piezoelectric ceramic composition according to the present invention is excellent in electric field deformation characteristics such as normalized strain (S _max / E _max ) by including high-energy ball milling as a medium and having a small- .

Accordingly, the lead-free piezoelectric ceramics composition of the present invention is not only environmentally friendly but also contains lead, has a high compactness by using a relaxed ferroelectric having a uniform particle size and narrow particle size distribution as a medium and has ferroelectric particles It has a dispersed structure and is excellent in electric field organic characteristics. In addition, since it is manufactured through a high energy ball-milling treatment, it is advantageous that process time and process temperature are easily controlled, thereby improving process efficiency and process cost.

Claims (15)

delete delete delete delete delete delete (Bi) -based relaxation type ferroelectric material represented by the following formula (1) was obtained from the mixture obtained by performing ball milling of Bi ₂ O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , TiO ₂ , La ₂ O ₅ and Fe ₂ O ₅ Producing;
Performing high-energy ball milling of the produced bismuth (Bi) -based relaxed ferroelectric material to crush the relaxed ferroelectric material;
Mixing a milled bismuth (Bi) -based relaxation type ferroelectric and a bismuth (Bi) -based ferroelectric to form a mixture; And
And sintering the molded product to manufacture a lead-free piezoelectric ceramic composition,
The high energy ball milling is carried out at a speed of from 700 to 950 rpm for from 10 to 100 minutes using at least three milling balls,
The milling balls are used in an amount of 2 to 5 parts by weight based on 1 part by weight of the bismuth (Bi) based relaxation type ferroelectric,
The sintering is performed at 950 to 1150 캜 for 1 to 3 hours,
A milled bismuth relaxation type ferroelectric has an average particle size of 1 to 50 占 퐉 and satisfies the following condition (3):
[Chemical Formula 1]
(1-x) [Bi _1/2 (Na _(1-y) K _y ) _1/2 TiO ₃ ] -xLaFeO ₃
In Formula 1,
x is 0.018 to 0.035, and
y is from 0.16 to 0.25;
&Quot; (3) "
(SH _30m - SH _0m ) / SH _0m ? 0.15
In Equation (3)
The SH _{30 m} represents the firing shrinkage at 1100 ° C of the relaxed ferroelectric material subjected to the high energy ball milling for 30 minutes,
SH _0m represents the firing shrinkage at 1100 ° C of the relaxed ferroelectric material subjected to high energy ball milling for 0 minutes.
delete delete delete 8. The method of claim 7,
The step of producing the bismuth (Bi) -based relaxed ferroelectric material includes:
Weighing Bi ₂ O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , TiO ₂ , La ₂ O ₅ and Fe ₂ O ₅ , respectively, and performing wet milling by ball milling;
Drying the wet mixed mixture; And
And calcining the dried mixture. ≪ RTI ID = 0.0 > 11. < / RTI >
8. The method of claim 7,
The bismuth (Bi) based ferroelectric is a compound represented by the following formula (2)
Wherein the mixing amount of the Bi-based relaxed ferroelectric is 5 to 55 parts by weight based on 100 parts by weight of the Bi-based relaxed ferroelectric.
(2)
_{Bi 1/2 (Na (1} -z) K z) 1/2 TiO 3
In Formula 2,
z is 0.16-0.22.
delete delete A piezoelectric body manufactured using the lead-free piezoelectric ceramic composition produced according to claim 7; And
And at least a pair of electrodes supported in contact with the piezoelectric body.

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