WO2023113306A1 - Core-shell structured lead-free piezoelectric ceramic having excellent piezoelectric and dielectric properties, and method for manufacturing same - Google Patents

Abstract

The present invention pertains to a core-shell structured lead-free piezoelectric ceramic having excellent piezoelectric and dielectric properties. More specifically, the present invention pertains to a core-shell structured lead-free piezoelectric ceramic having excellent piezoelectric and dielectric properties, and a method for manufacturing same, wherein the core-shell structured lead-free piezoelectric ceramic is formed by synthesizing Bi₂O₃-doped LNKN powder and then coating the surface of the Bi₂O₃-doped LNKN powder with BNK (Bi₂O₃-0.78Na₂O-0.22K₂O) having Bi, Na, and K components, thus enabling low-temperature firing and making it possible to achieve excellent density and piezoelectric and dielectric properties, even at low sintering temperatures.

Description

Core-shell structure lead-free piezoelectric ceramic with excellent piezoelectric and dielectric properties and manufacturing method thereof

The present invention relates to a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties and a method for manufacturing the same, and more particularly, to a surface of LNKN powder doped with Bi ₂ O ₃ after synthesis of LNKN powder doped with Bi ₂ O ₃ BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O) having Bi, Na, and K components is coated on the surface to form a core-shell structure lead-free piezoelectric ceramic, enabling low-temperature firing and low sintering. It relates to a lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties capable of securing excellent density, piezoelectric and dielectric properties even at high temperature and a method for manufacturing the same.

Piezoelectric ceramics are used to output an electrical signal having a wavelength with respect to physical pressure so as to induce vibration by input power.

To this end, Pb(Zr,Ti)O ₃ -based ceramics having excellent piezoelectric properties are used as piezoelectric ceramics.

However, since PZT-based piezoelectric ceramics contain lead (Pb), not only are they harmful to the human body and cause environmental pollution, but also there is a tendency for restrictions on their use due to strengthened regulations.

In addition, PZT series piezoelectric ceramics cause loss of electric signals supplied to the piezoelectric ceramic body, and are designed in a structure in which power cables are simply connected to the piezoelectric ceramic body by soldering, so the binding of the power cables is not perfect. there was

As a related prior literature, there is Korean Patent Publication No. 10-2004-0054965 (published on June 26, 2004), which describes lead-free piezoelectric ceramics and a manufacturing method thereof.

An object of the present invention is to synthesize LNKN powder doped with Bi ₂ O ₃ , and then BNK (Bi _{2 O 3 -0.78Na 2} O-0.22K) having Bi, Na and K components on the surface of the LNKN powder doped with Bi ₂ O 3 . ₂ O) to form a lead-free piezoelectric ceramic with a core-shell structure, enabling low-temperature firing, and a core-shell structure with excellent piezoelectric and dielectric properties that can secure excellent density, piezoelectric and dielectric properties even at low sintering temperatures It is to provide a lead-free piezoelectric ceramic and a manufacturing method thereof.

In order to achieve the above object, a method for manufacturing a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention is (a) (Li _1-x Na _1-y K _1-z )NbO ₃ (where , x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8), Bi ₂ O ₃ is added to the LNKN piezoelectric material having a composition ratio to synthesize LNKN powder doped with Bi ₂ O ₃ step; (b) After weighing Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ to have a composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), an acidic solution was added and stirred to obtain a BNK coating solution forming a; (c) forming lead-free piezoelectric ceramic powder having a core-shell structure by mixing a BNK coating solution and a binder with the LNKN powder doped with Bi ₂ O ₃ , ball milling, drying, and grinding; (d) forming a core-shell structure lead-free piezoelectric ceramic molded body by calcining the lead-free piezoelectric ceramic powder having a core-shell structure, adding a binder, and press-molding; and (e) step of sintering the lead-free piezoelectric ceramic molded body of the core-shell structure in two steps, wherein in the step (e), the two-step sintering is performed at 650 to 800 ° C. It is characterized by secondary sintering at 1,150 ° C.

In the step (a), the Bi ₂ O ₃ is added in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of the LNKN piezoelectric material.

In the step (c), the BNK coating solution is added in an amount of 15 to 30 parts by weight based on 100 parts by weight of the LNKN powder doped with Bi ₂ O ₃ .

In the step (d), the pressure molding is performed at 100 to 180° C. under a pressure condition of 1 to 3 ton/cm 2 for 1 to 60 minutes.

In the step (e), the two-step sintering includes the steps of primary sintering at 650 to 800 ° C for 10 to 60 minutes and secondary sintering at 950 to 1,150 ° C for 30 to 240 minutes. do.

In order to achieve the above object, a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention includes a core layer made of LNKN doped with Bi ₂ O ₃ and disposed to cover the surface of the core layer. and a lead-free piezoelectric ceramic body including a BNK coating layer composed of Bi, Na and K components; and a skin current connection electrode disposed on at least one surface of the lead-free piezoelectric ceramic body, wherein the skin current connection electrode includes an inner hollow connection electrode disposed at an inner central portion and an outer side spaced apart from the inner hollow connection electrode. It has an outer hollow connection electrode arranged to have a cone shape surrounding the inner hollow connection electrode, and a plurality of air outlets formed to penetrate the lower side of the outer hollow connection electrode, and the inner hollow connection electrode has a bottom surface of the lead-free piezoelectric ceramic body. Is connected to, a hollow cooling hole is disposed in the center, a heat dissipation groove is provided on the inner wall of the hollow cooling hole, and the LNKN is (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is 0.8 ~ 0.99, y is 0.3 ~ 0.7, and z is 0.5 ~ 0.8).

The outer hollow connection electrode is provided with a cable insertion hole for inserting a power cable into a space between the inner hollow connection electrode, and a bottom surface thereof is connected to the lead-free piezoelectric ceramic body.

The external hollow connection electrode is formed to pass through a lower portion of the external hollow connection electrode and has a plurality of air outlets for discharging internal air to the outside so that solder filled into the cable insertion hole flows.

The plurality of air outlets are formed to pass through a lower portion of the external hollow connection electrode, and pass through a first air outlet disposed at a first position and a lower portion of the external hollow connection electrode, the first position It has a second air outlet spaced apart from the first air outlet at a higher second position in a zigzag pattern.

The skin current connection electrode is disposed to be spaced apart from the bottom surface of the external hollow connection electrode in contact with the lead-free piezoelectric ceramic body, and a vibration damping cutout disposed at a second position corresponding to the second air outlet. It further includes.

In the lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties and a method for manufacturing the same according to the present invention, Bi ₂ O ₃ -doped LNKN powder is synthesized, and then Bi, Na and K are formed on the surface of the Bi ₂ O ₃ -doped LNKN powder. As BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O) having a component is coated on the surface to form a core-shell structure lead-free piezoelectric ceramic, low-temperature firing is possible, and excellent density and piezoelectricity even at low sintering temperatures And dielectric properties can be secured.

In addition, the lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties and a method for manufacturing the same according to the present invention include a lead-free core-shell structure composed of a Bi ₂ O ₃ -doped LNKN-based core layer and a BNK-based coating layer. By being composed of a piezoelectric ceramic body and a skin current connection electrode provided on at least one surface of the lead-free piezoelectric ceramic body, environmental pollution is minimized because lead is not added, and electricity is transmitted to the lead-free piezoelectric ceramic body through the skin current connection electrode. Not only can the signal supply be stably transmitted without loss, but also the reliability of the binding of the power cable can be secured.

In addition, in the lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties and the manufacturing method according to the present invention, the external hollow connection electrode of the skin current connection electrode is formed in a cone shape, and the extension of the cone is bound to the lead-free piezoelectric ceramic body. And, the area becomes wider toward the lead-free piezoelectric ceramic body, so that the internal resistance can be minimized.

In addition, a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties and a manufacturing method thereof according to the present invention have a first air outlet disposed at a first position and a second air outlet disposed at a second position higher than the first position. By disposing them spaced apart from each other in a zigzag form, passages through which solder can be discharged can be further increased without interference between the first and second air outlets.

Accordingly, the lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties and a method for manufacturing the same according to the present invention solder a power cable to the lead-free piezoelectric ceramic body side for connection of an internal hollow connection electrode and an external hollow connection electrode. During the process, the inside air is discharged to the outside so that the inflowing solder flows more smoothly, and the air outlets are spaced apart in a zigzag pattern so that the solder is stably bound, so that the connection of the power cable is stable and signal loss is minimized. It has structural advantages.

1 is a process flow chart showing a method for manufacturing a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention.

2 is a perspective view illustrating a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention.

3 is a cross-sectional view showing a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention.

4 is an enlarged perspective view of the skin current connection electrode of FIG. 2;

5 is an enlarged perspective view of a skin current connection electrode according to a modified example of the present invention;

6 is a cross-sectional view taken along the line VI-VI' of FIG. 5;

7 is an enlarged cross-sectional view of part A of FIG. 6;

Advantages and features of the present invention, and methods of achieving them, will become clear with reference to the detailed description of the following embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but will be implemented in various different forms, and only these embodiments make the disclosure of the present invention complete, and common knowledge in the art to which the present invention belongs. It is provided to fully inform the holder of the scope of the invention, and the present invention is only defined by the scope of the claims. Like reference numbers designate like elements throughout the specification.

Hereinafter, a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to a preferred embodiment of the present invention and a manufacturing method thereof will be described in detail with reference to the accompanying drawings.

1 is a process flow chart illustrating a method for manufacturing a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention.

As shown in FIG. 1, the method for manufacturing a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention includes synthesizing LNKN powder doped with Bi ₂ O ₃ (S110), forming a BNK coating solution A step (S120), a step of forming lead-free piezoelectric ceramic powder having a core-shell structure (S130), a step of forming a lead-free piezoelectric ceramic molded body having a core-shell structure (S140), and a sintering step (S150).

Synthesis of LNKN powder doped with Bi ₂ O ₃

In the step of synthesizing LNKN powder doped with Bi ₂ O ₃ (S110), (Li _1-x Na _1-y K _1-z )NbO ₃ (hereinafter, abbreviated as LNKN) (where x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8), Bi ₂ O ₃ is added to the LNKN piezoelectric material having a composition ratio to synthesize LNKN powder doped with Bi ₂ O ₃ .

Here, Bi ₂ O ₃ is doped to improve density, piezoelectric and dielectric properties. To this end, Bi ₂ O ₃ is preferably added in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of the LNKN piezoelectric material. When Bi ₂ O ₃ is added in an amount of less than 0.1 part by weight based on 100 parts by weight of the LNKN piezoelectric material, the added amount is insignificant, making it difficult to properly exhibit the effect of improving density, piezoelectricity, and dielectric properties. Conversely, when a large amount of Bi ₂ O ₃ is added in excess of 0.5 parts by weight based on 100 parts by weight of the LNKN piezoelectric material, it is not economical because only a large amount of Bi ₂ O ₃ is required without further enhancing the effect.

BNK coating solution formation

In the BNK coating solution forming step (S120), Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ are weighed to have a composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), and then an acidic solution is added and stirred to form a BNK coating solution.

At this time, it is preferable to add each raw material of Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ sequentially after confirming that complete dissolution is made at intervals of 10 minutes. As the acidic solution, at least one selected from among nitric acid, hydrochloric acid and sulfuric acid may be used.

In this step, stirring is preferably performed for 1 to 12 hours at a speed of 300 to 700 rpm.

If the stirring speed is less than 300 rpm or the stirring time is less than 1 hour, there is a concern that uniform mixing between each raw material of Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ and the acidic solution may not be achieved. Conversely, when the stirring speed exceeds 700 rpm or the stirring time exceeds 12 hours, it is not economical because it may act as a factor that only increases manufacturing cost without further effect.

At the time of such stirring, it is more preferable to perform ultrasonic treatment together under conditions of 30 to 50 kHz and 150 to 250 W of output power. In this way, after weighing Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ to have a composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), in the process of adding an acidic solution and stirring, When ultrasonic treatment is performed together, when bubble collapse occurs after a certain period of time, a temperature of 5000K locally, a pressure of about 1000bar, and heating and cooling rates of 10 ¹⁰ K/s are extreme conditions. (extreme condition), it is possible to maximize the dispersion efficiency.

At this time, when the ultrasonic output power is less than 150 W, despite the ultrasonic treatment, there is a concern that uniform mixing between each raw material of Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ and the acidic solution may not be achieved, which is not preferable. . Conversely, when the ultrasonic output power exceeds 250 W, there is a risk of damaging each raw material of Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ due to excessive ultrasonic treatment, which is not preferable.

Core-shell structure lead-free piezoelectric ceramic powder formation

In the step of forming the lead-free piezoelectric ceramic powder having a core-shell structure (S130), the LNKN powder doped with Bi ₂ O ₃ is mixed with a BNK coating solution and a binder, ball-milled, dried and pulverized to obtain a lead-free piezoelectric ceramic powder having a core-shell structure. form

Here, the binder may use at least one selected from polyvinyl alcohol (PVA), polyvinyl butyral (PVB), and polyethylene glycol (PEG), among which polyvinyl alcohol It is more preferable to use When polyvinyl alcohol is used as a binder, when the negative charge of (-OH) in PVA is 1, the charges of Bi ³⁺ , Na ⁺ and K ⁺ are calculated and added in a ratio of 1: 1 it is desirable

Here, the ball milling method is preferably carried out for 10 to 30 hours after adding the LNKN powder doped with Bi ₂ O ₃ , the BNK coating solution, and the binder to the zirconia ball.

At this time, drying may be carried out for 5 to 20 hours at 100 ~ 150 ℃.

In this step, the BNK coating solution is preferably added in an amount of 15 to 30 parts by weight, based on 100 parts by weight of the LNKN powder doped with Bi ₂ O ₃ , and a more preferable range is 20 to 25 parts by weight. When the BNK coating solution is added in an amount of less than 15 parts by weight based on 100 parts by weight of the LNKN powder doped with Bi ₂ O ₃ , there is a concern that the LNKN powder doped with Bi ₂ O ₃ may not be perfectly coated with BNK due to an insignificant amount added. there is Conversely, when the BNK coating solution is added in an amount exceeding 30 parts by weight based on 100 parts by weight of the LNKN powder doped with Bi ₂ O ₃ , piezoelectric performance may be deteriorated, which is not preferable.

Formation of lead-free piezoelectric ceramic molded body with core-shell structure

In the step of forming the core-shell structure lead-free piezoelectric ceramic molded body (S140), the core-shell structure lead-free piezoelectric ceramic powder is calcined, and then a binder is added and pressure-molded to form a lead-free piezoelectric ceramic molded body with a core-shell structure.

At this time, the pressure molding is preferably performed for 1 to 60 minutes under a pressure condition of 1 to 3 ton/cm 2 at 100 to 180° C.

When the pressure molding temperature is less than 100° C. or the pressure molding time is less than 1 minute, there is a high risk that sufficient curing may not be achieved. Conversely, when the pressure molding temperature exceeds 180° C. or the pressure molding time exceeds 60 minutes, it is not economical because it may act as a factor that only increases manufacturing cost without a significant change in physical properties.

In addition, when the compression molding pressure is less than 1 ton/cm 2 , it may be difficult to secure strength. Conversely, when the compression molding pressure exceeds 3 ton/cm 2 , the shape of the lead-free piezoelectric ceramic molded body having a core-shell structure may be deformed due to the excessive pressure.

sintering

In the sintering step (S150), the core-shell structure of the lead-free piezoelectric ceramic molded body is sintered in two stages.

In this step, the two-stage sintering includes a first sintering process at 650 ~ 800 ° C. for 10 ~ 60 minutes, and a second sintering process at 950 ~ 1,150 ° C. for 30 ~ 240 minutes. In this way, when performing the first sintering at a low temperature of 650 ~ 800 ° C. and then performing the second sintering at a high temperature of 950 ~ 1,150 ° C., it is possible to carry out sintering while gradually raising the temperature. , it is possible to prevent cracks from occurring in the lead-free piezoelectric ceramic molded body due to rapid temperature changes. As a result, it is possible to manufacture a lead-free piezoelectric ceramic having excellent piezoelectric and dielectric properties and high strength.

At this time, when the secondary sintering temperature is less than 950° C. or the secondary sintering time is less than 30 minutes, it may be difficult to secure target strength, density, piezoelectric and dielectric properties. Conversely, when the secondary sintering temperature exceeds 1,150° C. or the secondary sintering time exceeds 240 minutes, the strength may increase, but piezoelectric and dielectric properties are poor.

As described above, the method for manufacturing a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention may be completed.

In the above-described method for manufacturing lead-free piezoelectric ceramics having a core-shell structure according to an embodiment of the present invention, after synthesizing LNKN powder doped with Bi ₂ O ₃ , Bi ₂ O ₃ has Bi, Na, and K components on the surface of the LNKN powder doped. BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O) is coated on the surface to form a core-shell structure lead-free piezoelectric ceramic, enabling low-temperature firing and excellent density, piezoelectric and dielectric properties even at low sintering temperatures can be obtained.

In addition, the method for manufacturing a lead-free piezoelectric ceramic having a core-shell structure according to an embodiment of the present invention includes a lead-free piezoelectric ceramic body having a core-shell structure composed of a core layer composed of LNKN-based doped with Bi ₂ O ₃ and a coating layer composed of BNK-based; By being composed of skin current connection electrodes provided on at least one surface of the lead-free piezoelectric ceramic body, environmental pollution is minimized because lead is not added, and electrical signals are supplied to the lead-free piezoelectric ceramic body through the skin current connection electrode without loss. Not only can it be stably transmitted, but also it is possible to secure the reliability of the binding of the power cable.

Hereinafter, a lead-free piezoelectric ceramic having a core-shell structure having excellent piezoelectric and dielectric properties according to embodiments of the present invention will be described in more detail with reference to the accompanying drawings.

2 is a perspective view showing a lead-free piezoelectric ceramic having a core-shell structure excellent in piezoelectric and dielectric properties according to an embodiment of the present invention, and FIG. 3 is a lead-free piezoelectric ceramic having a core-shell structure excellent in piezoelectric and dielectric properties according to an embodiment of the present invention. A cross-sectional view showing a ceramic, and FIG. 4 is an enlarged perspective view of the skin current connection electrode of FIG. 2 .

2 to 4, the lead-free piezoelectric ceramic 200 having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention includes a lead-free piezoelectric ceramic body 220 and a skin current connection electrode 240. do.

The lead-free piezoelectric ceramic body 220 includes a core layer made of LNKN doped with Bi ₂ O ₃ , and a BNK coating layer made of Bi, Na, and K components disposed to cover the surface of the core layer. Here, LNKN has a composition ratio of (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8).

The skin current connecting electrode 240 is disposed on at least one surface of the lead-free piezoelectric ceramic body 220 .

The skin current connection electrode 240 has an inner hollow connection electrode 241, an outer hollow connection electrode 242, and an air outlet 244.

The internal hollow connection electrode 241 is disposed in the inner central portion and may have a hollow pipe shape with an empty central portion. The bottom surface of this internal hollow connection electrode 241 is connected to the lead-free piezoelectric ceramic body 220, and a hollow cooling hole 245 is disposed in the center.

Here, the hollow cooling hole 245 is disposed in an empty hollow structure in the inner center of the inner hollow connection electrode 241 . In the natural cooling method through the hollow cooling hole 245, heat can be smoothly dissipated by smooth air flow inside the internal hollow connection electrode 241.

The outer hollow connection electrode 242 is disposed to have a cone shape surrounding the inner hollow connection electrode 241 from the outside spaced apart from the inner hollow connection electrode 241 . The outer hollow connection electrode 242 is provided with a cable insertion hole 243 for inserting a power cable into a space between the inner hollow connection electrode 241, and the bottom surface is connected to the lead-free piezoelectric ceramic body 220.

Here, the external hollow connection electrode 242 is formed to penetrate the lower portion of the external hollow connection electrode 242, and a plurality of air outlets for discharging internal air to the outside so that the solder filled in the cable insertion hole flows smoothly ( 244).

The plurality of air outlets 244 are formed to pass through the lower portion of the external hollow connection electrode 242, and the first air outlet 244a disposed in the first position and the lower portion of the external hollow connection electrode 242 It is more preferable to have a second air outlet 244b spaced apart from the first air outlet 244a in a zigzag shape at a second position higher than the first position.

In this way, the plurality of air outlets 244 are spaced apart from each other in a zigzag pattern with the first air outlet 244a disposed at the first position and the second air outlet 244b disposed at the second position higher than the first position. If so, it is possible to have a structural advantage of further increasing the passage through which solder can be discharged without mutual interference, compared to arranging them at the same location. As a result, since the air inside the external hollow connection electrode 242 can be smoothly discharged to the outside through the air outlet 244 having a zigzag arrangement structure, it is possible to more smoothly flow the solder filled into the cable insertion hole. be able to

As described above, the lead-free piezoelectric ceramic 200 having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention has a core layer composed of a Bi ₂ O ₃ -doped LNKN-based core layer and a BNK-based coating layer composed of a core shell. By being composed of the lead-free piezoelectric ceramic body 220 of the structure and the skin current connection electrode 240 provided on at least one surface of the lead-free piezoelectric ceramic body 220, lead is not added and environmental pollution is minimized, and the skin Electrical signals supplied to the lead-free piezoelectric ceramic body 220 through the current connection electrode 240 can be stably transmitted without loss, and reliability of the binding of the power cable can be secured.

In addition, in the lead-free piezoelectric ceramic 200 having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention, the external hollow connection electrode 242 of the skin current connection electrode 240 is formed in a cone shape, and the cone The expansion unit is bound to the lead-free piezoelectric ceramic body 220, and its area increases toward the lead-free piezoelectric ceramic body 220, so that internal resistance can be minimized.

In addition, the lead-free piezoelectric ceramic 200 having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention is disposed at a first air outlet 244a disposed at a first position and at a second position higher than the first position. By arranging the second air outlets 244b spaced apart from each other in a zigzag pattern, it is possible to further increase the passage through which the solder can be discharged without interference between the first and second air outlets 244a and 244b. .

Accordingly, the lead-free piezoelectric ceramic 200 having a core-shell structure having excellent piezoelectric and dielectric properties according to an embodiment of the present invention is a lead-free piezoelectric ceramic for connection of the inner hollow connection electrode 241 and the outer hollow connection electrode 242. During the process of soldering the power cable on the main body 220 side, the air outlet 244 is spaced apart in a zigzag pattern so that the incoming solder flows more smoothly, discharges internal air to the outside, and stabilizes the solder. It has a structural advantage that the connection of the power cable can be made stably and signal loss can be minimized.

Meanwhile, FIG. 5 is an enlarged perspective view of a skin current connection electrode according to a modified example of the present invention, FIG. 6 is a cross-sectional view taken along line VI-VI' in FIG. 5, and FIG. 7 is FIG. 6 It is a cross-sectional view showing an enlarged portion of A of .

First, as shown in FIG. 5, the skin current connection electrode 200 according to the modified example of the present invention is according to the embodiment described with reference to FIG. 4, except for further having a vibration damping cutout 246. Since it is substantially the same as the skin current connection electrode, redundant explanation will be omitted and the difference will be mainly explained.

That is, the skin current connection electrode 240 according to the modified example of the present invention has a vibration damping cutout 246 disposed on the bottom surface of the external hollow connection electrode 242 in contact with the lead-free piezoelectric ceramic body (220 in FIG. 2). contains more

At this time, when the vibration damping cutout 246 is formed at a portion corresponding to the first position where the first air outlet 244a is disposed, the space may be narrower at a position closer to the lead-free piezoelectric ceramic body than at the second position. There is a risk of damaging the first and second air outlets 244a and 244b. Accordingly, it is preferable that the vibration damping cutout 246 be spaced apart at regular intervals at the second position corresponding to the second air outlet 244b. The vibration damping cutout 246 may have a triangular shape when viewed in cross section, but this is exemplary and the shape may be variously changed.

As described above, in the skin current connection electrode 240 according to the modified example of the present invention, since the vibration damping cutout 246 is spaced apart at regular intervals at the second position corresponding to the second air outlet 244b, the lead-free piezoelectric Attenuation due to the internal and external hollow connection electrodes 241 and 242 can be minimized during vibration caused by the supply of electrical signals to the ceramic body 220 .

In addition, as shown in FIGS. 6 and 7, the skin current connection electrode 240 according to the modified example of the present invention has only a difference in the detailed configuration of the inner hollow connection electrode 241, as described with reference to FIG. Since it is substantially the same as the skin current connection electrode according to the embodiment, redundant description will be omitted and the difference will be mainly described.

The inner hollow connection electrode 241 according to the modified example of the present invention has a bottom surface connected to a lead-free piezoelectric ceramic body (200 in FIG. 2), a hollow cooling hole 245 is disposed in the center, and a hollow cooling hole 245 A heat dissipation groove (T) is provided on the inner wall of the.

In addition, the internal hollow connection electrode 241 according to the modified example of the present invention further includes a heat dissipation protrusion 247 disposed in the heat dissipation groove T.

It is preferable that the heat dissipation protrusion 247 is formed in an integral structure with the internal hollow connection electrode 241 to secure durability. At this time, a plurality of heat dissipation protrusions 247 protrude in a hemispherical shape within the heat dissipation groove T, and it is preferable to arrange them so that they are spaced apart from each other at regular intervals. As such, the internal hollow connection electrode 241 according to the modified example of the present invention has a plurality of heat dissipation protrusions 247 protruding in a hemispherical shape in the heat dissipation groove T, so that the surface area can be increased and the hollow cooling By increasing the contact area with the air introduced through the sphere 245, the heat dissipation effect can be further maximized.

Example

Hereinafter, the configuration and operation of the present invention will be described in more detail through preferred embodiments of the present invention. However, this is presented as a preferred example of the present invention and cannot be construed as limiting the present invention by this in any sense.

Contents not described herein can be technically inferred by those skilled in the art, so descriptions thereof will be omitted.

1. Manufacture of lead-free piezoelectric ceramics

Example 1

LNKN powder doped with Bi 2 O ₃ was synthesized by adding _0.3 parts by weight of Bi ₂ O 3 to 100 parts by weight of the LNKN piezoelectric material having _a composition ratio of (Li _0.05 Na _0.57 K _0.38 ) NbO ₃ .

Next, Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ were weighed to have a composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), and then added to 1M HNO ₃ at a rate of 500 rpm. A BNK coating solution was prepared by stirring for 6 hours.

Next, the LNKN powder doped with Bi ₂ O ₃ was mixed with a BNK coating solution and a binder, ball milled for 20 hours, dried at 110 ° C. for 24 hours, and then pulverized to prepare lead-free piezoelectric ceramic powder having a core-shell structure. did At this time, 20 parts by weight of the BNK coating solution was added based on 100 parts by weight of the LNKN powder doped with Bi ₂ O ₃ .

Next, the lead-free piezoelectric ceramic powder having a core-shell structure was calcined at 650° C. for 3 hours, and then a binder, PVA aqueous solution (5 wt%) was added, and pressure molding was performed at 150° C. for 30 minutes under a pressure condition of 2 ton/cm 2 . A lead-free piezoelectric ceramic molded body having a core-shell structure was prepared.

Next, the lead-free piezoelectric ceramic molded body having a core-shell structure was firstly sintered at 700° C. for 30 minutes and then secondarily sintered at 1,100° C. for 120 minutes to prepare lead-free piezoelectric ceramics.

Example 2

When preparing the BNK coating solution, a lead-free piezoelectric ceramic was prepared in the same manner as in Example 1, except that ultrasonic treatment was performed at 40 kHz and 200 W of output power.

Example 3

A lead-free piezoelectric ceramic was manufactured in the same manner as in Example 1, except for primary sintering at 650° C. for 50 minutes and then secondary sintering at 1,000° C. for 200 minutes.

Example 4

A lead-free piezoelectric ceramic was manufactured in the same manner as in Example 1, except for primary sintering at 750° C. for 20 minutes and then secondary sintering at 1,050° C. for 180 minutes.

Comparative Example 1

LNKN powder doped with Bi 2 O ₃ was synthesized by adding _0.3 parts by weight of Bi ₂ O 3 to 100 parts by weight of the LNKN piezoelectric material having _a composition ratio of (Li _0.05 Na _0.57 K _0.38 ) NbO ₃ .

Next, the LNKN powder doped with Bi ₂ O ₃ was calcined at 600° C. for 2 hours, and then a PVA aqueous solution (5 wt%) as a binder was added and pressure-molded at 150° C. for 30 minutes under a pressure condition of 2 ton/cm 2 . Thus, a lead-free piezoelectric ceramic molded body was manufactured.

Next, the lead-free piezoelectric ceramic molded body was sintered at 1,100° C. for 3 hours to prepare a lead-free piezoelectric ceramic.

2. Property evaluation

Table 1 shows the evaluation results of physical properties of the lead-free piezoelectric ceramics prepared according to Examples 1 to 4 and Comparative Example 1. At this time, in order to measure the electrical properties, the lead-free piezoelectric ceramics prepared according to Examples 1 to 4 and Comparative Example 1 were polished to a thickness of 1 mm, Ag electrodes were applied, and after heat treatment, 30 kV / cm in insulating oil at 120 ° C. Polarization treatment was performed by applying a DC electric field of 30 minutes, and electrical characteristics were measured after 24 hours. In addition, dielectric properties were measured using an LCR meter (AN DO AG-4304).

[Table 1]

As shown in Table 1, the lead-free piezoelectric ceramics prepared according to Examples 1 to 4 had higher sintered densities than the lead-free piezoelectric ceramics prepared according to Comparative Example 1, as well as piezoelectric and dielectric properties. It can be seen that the physical properties are significantly improved.

As can be seen based on the above experimental results, the lead-free piezoelectric ceramics according to Examples 1 to 4 subjected to two-step sintering exhibit superior piezoelectric and dielectric properties compared to the lead-free piezoelectric ceramics according to Comparative Example 1 subjected to one-step sintering. Confirmed.

The present invention is a material parts technology development project supervised by the Korea Evaluation Institute of Industrial Technology of the Ministry of Trade, Industry and Energy in 2021, "Development of bismuth-based coe-shell lead-free piezoelectric material for biomedical piezoelectric sensor (Task identification number: 1415175377, R&D task number: 20016729).

Although the above has been described based on the embodiments of the present invention, various changes or modifications may be made at the level of a technician having ordinary knowledge in the technical field to which the present invention belongs. Such changes and modifications can be said to belong to the present invention as long as they do not deviate from the scope of the technical idea provided by the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

[Description of code]

S110: Synthesis of LNKN powder doped with Bi ₂ O ₃

S120: BNK coating solution formation step

S130: Core-shell structure lead-free piezoelectric ceramic powder forming step

S140: Step of forming a lead-free piezoelectric ceramic molded body with a core-shell structure

S150: sintering step

200: Lead-free piezoelectric ceramic with core-shell structure 220: Lead-free piezoelectric ceramic body

240: skin current connection electrode 241: inner hollow connection electrode

242: external hollow connection electrode 243: cable insertion hole

244: air outlet 244a: first air outlet

244b: second air outlet 245: hollow cooling port

246: Vibration damping cutout 247: Heat radiation protrusion

T: heat dissipation groove

Claims (10)

1. (a) LNKN piezoelectric having a composition ratio of (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8) synthesizing LNKN powder doped with Bi ₂ O ₃ by adding Bi ₂ O ₃ to the material;

   (b) After weighing Bi(NO ₃ ) ₃ , NaNO ₃ and KNO ₃ to have a composition of BNK (Bi ₂ O ₃ -0.78Na ₂ O-0.22K ₂ O), an acidic solution was added and stirred to obtain a BNK coating solution forming a;

   (c) forming lead-free piezoelectric ceramic powder having a core-shell structure by mixing a BNK coating solution and a binder with the LNKN powder doped with Bi ₂ O ₃ , ball milling, drying, and grinding;

   (d) forming a core-shell structure lead-free piezoelectric ceramic molded body by calcining the lead-free piezoelectric ceramic powder having a core-shell structure, adding a binder, and press-molding; and

   (e) sintering the lead-free piezoelectric ceramic molded body of the core-shell structure in two steps;

   In the step (e), the two-stage sintering is a lead-free piezoelectric ceramic of a core-shell structure with excellent piezoelectric and dielectric properties, characterized in that the primary sintering at 650 ~ 800 ° C, followed by the secondary sintering at 950 ~ 1,150 ° C. manufacturing method.
2. According to claim 1,

   In step (a),

   The Bi ₂ O ₃ is

   A lead-free piezoelectric ceramic manufacturing method of a core-shell structure with excellent piezoelectric and dielectric properties, characterized in that it is added in an amount of 0.1 to 0.5 parts by weight based on 100 parts by weight of the LNKN piezoelectric material.
3. According to claim 1,

   In step (c),

   The BNK coating solution is

   15 to 30 parts by weight based on 100 parts by weight of the Bi ₂ O ₃ doped LNKN powder.
4. According to claim 1,

   In step (d),

   The pressure molding

   A lead-free piezoelectric ceramic manufacturing method of a core-shell structure with excellent piezoelectric and dielectric properties, characterized in that carried out for 1 to 60 minutes under a pressure condition of 1 to 3 ton / cm 2 at 100 to 180 ° C.
5. According to claim 1,

   In step (e),

   The two-stage sintering

   Primary sintering at 650 to 800 ° C. for 10 to 60 minutes;

   A lead-free piezoelectric ceramic manufacturing method of a core-shell structure with excellent piezoelectric and dielectric properties, comprising the step of secondary sintering at 950 to 1,150 ° C. for 30 to 240 minutes.
6. a lead-free piezoelectric ceramic body including a core layer made of LNKN doped with Bi ₂ O ₃ , and a BNK coating layer disposed to cover a surface of the core layer and made of Bi, Na, and K components; and

   A skin current connection electrode disposed on at least one surface of the lead-free piezoelectric ceramic body; includes,

   The skin current connection electrode includes an inner hollow connection electrode disposed at an inner central portion, an outer hollow connection electrode disposed to have a cone shape surrounding the inner hollow connection electrode at an outer space spaced from the inner hollow connection electrode, and the outer hollow connection electrode. It has a plurality of air outlets formed to pass through the lower side of the connection electrode,

   The inner hollow connection electrode has a bottom surface connected to the lead-free piezoelectric ceramic body, a hollow cooling hole is disposed in the center, and a heat dissipation groove is provided on an inner wall of the hollow cooling hole,

   The LNKN has a composition ratio of (Li _1-x Na _1-y K _1-z )NbO ₃ (where x is 0.8 to 0.99, y is 0.3 to 0.7, and z is 0.5 to 0.8). A lead-free piezoelectric ceramic with a core-shell structure with excellent piezoelectric and dielectric properties.
7. According to claim 6,

   The external hollow connection electrode is

   A lead-free piezoelectric ceramic having a core-shell structure with excellent piezoelectric and dielectric properties, characterized in that a cable insertion hole for inserting a power cable is provided in the space between the inner hollow connection electrode and the bottom surface is connected to the lead-free piezoelectric ceramic body. .
8. According to claim 6,

   The external hollow connection electrode is

   A core having excellent piezoelectric and dielectric properties, characterized in that it is formed to penetrate the lower part of the external hollow connection electrode and has a plurality of air outlets for discharging internal air to the outside so that the solder filled into the cable insertion hole flows. Lead-free piezoelectric ceramic with shell structure.
9. According to claim 8,

   The plurality of air outlets

   a first air outlet formed to pass through a lower portion of the external hollow connection electrode and disposed in a first position;

   It is formed to penetrate the lower part of the external hollow connection electrode and has a second air outlet spaced apart from the first air outlet in a zigzag form at a second position higher than the first position, characterized in that the piezoelectric and dielectric properties are Lead-free piezoelectric ceramic with excellent core-shell structure.
10. According to claim 9,

    The skin current connection electrode is

    a vibration damping cutout disposed on a bottom surface of the external hollow connection electrode in contact with the lead-free piezoelectric ceramic body and disposed at a second position corresponding to the second air outlet;

    Lead-free piezoelectric ceramic of a core-shell structure having excellent piezoelectric and dielectric properties, characterized in that it further comprises.

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