KR20210114671A - BiFeO3-BaTiO3 BASED ENVIRONMENT FRIENDLY LEAD-FREE PIEZOCERAMICS WITH PHYSICAL PROPERTIES AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

The present invention relates to eco-friendly lead-free piezoelectric ceramics expressed by (1-x)Bi_(1.03)FeO_3-x(Ba_(1-2y)Li_yAl_y)TiO_3 and a manufacturing method thereof, wherein 0.225 <= x <= 0.300 and 0.005<= y <= 0.020. Since the eco-friendly lead-free piezoelectric ceramics has excellent mechanical quality factor (Q_m), electromechanical coupling factor (k_P), and static piezoelectric constant (d_(33)) value while simultaneously having the high phase transition temperature of 300℃ or higher, the present invention can be usefully used as a core material for various ultrasonic elements or devices such as ultrasonic sensors, ultrasonic cleaners, and ultrasonic humidifiers.

Description

BiFeO3-BaTiO3 BASED ENVIRONMENT FRIENDLY LEAD-FREE PIEZOCERAMICS WITH PHYSICAL PROPERTIES AND MANUFACTURING METHOD THEREOF

The present invention relates to lead-free piezoelectric ceramics and a method for manufacturing the same, and more particularly, to an environmentally friendly lead-free piezoelectric ceramics that can replace commercial PZT piezoelectric ceramics with excellent physical properties and a method for manufacturing the same.

Currently, a piezoelectric material containing lead (Pb) centered on Pb(Zr,Ti)O ₃ (PZT) is widely used throughout industries such as fuel injectors, precision sensors, and actuators. However, lead, a heavy metal that accounts for more than 60% of its weight, has a low melting point, and a significant amount of fumes are generated between 500 and 600 ° C and act on the nervous system through the human respiratory system. .

In particular, the 'Restriction of Hazardous Substance (RoHS)' was promulgated in February 2003, mainly in the European Union, and in July 2006, lead (Pb), cadnium (Cd), mercury (Hg) ), hexavalent chromium (Cr), and bromine (Br)-based flame retardants are prohibited from being used. In addition, in August 2005, the Waste Electrical and Electronic Equipment (WEEE) was promulgated, which severely restricts the use of hazardous substances throughout the industry from production to disposal.

In response to global environmental regulations, the development of lead-free (lead-free) piezoelectric materials that do not contain heavy metals in the piezoelectric industry has been actively researched in recent years. In addition to the high piezoelectric properties of PZT-based ceramics, which are mainly used in industries, it has a very high phase transition temperature of 400 °C or higher. However, due to thermal depolarization and leakage current generated at high temperatures, the operating temperature for practical applications is limited to half the phase transition temperature. Therefore, in order for the lead-free piezoelectric material to substantially replace the PZT-based material, a high piezoelectric constant and a high phase transition temperature are required.

In order to replace PZT ceramics, there are studies on a bismuth layer structure, tungsten-bronze, etc., but currently, studies are being actively made on a material having the _{same perovskite (ABO 3 ) crystal structure as PZT.} Typically, bismuth (Bi)-based (Bi _0.5 Na _0.5 )TiO ₃ (BNT), (Bi _0.5 K _0.5 )TiO ₃ (BKT) and alkali metal-based NaNbO ₃ (NN) and KNbO ₃ ( Centering on KNN, which is a solid solution of KN), the results have been shown to have excellent piezoelectric constants that can compete with PZT. However, _{due to the high hygroscopicity of alkali metal raw materials such as Na 2} CO ₃ , K ₂ CO ₃ and the volatility during sintering, the composition region showing excellent piezoelectric properties is near room temperature or the phase transition temperature is below ^{~200 o C.} There are limitations in practical application due to problems formed in

_{However, recently, an eco-friendly lead-free piezoceramics BiFeO 3} -BaTiO ₃ (BF-BT) solid solution with properties completely different from those of BNT, BKT, and KNN has ^{a high phase transition temperature of 300 o} C or higher, which is comparable to that of commercial PZT, and electrical power of 0.3 or higher. Because it has a mechanical coupling coefficient ( k _P ) and a high static piezoelectric piezoelectric ( d ₃₃ ) characteristic of more than 300 pC/N, many studies are being conducted.

In order to use piezoelectric ceramics for applications such as ultrasonic vibrators, sensors, and oscillators, it is desirable that the electromechanical quality factor ( k _P ), the mechanical quality factor ( Q _m ), or the piezoelectric coefficient ( d ₃₃ ) have high values at the same time. However, as the reflow temperature rises due to the use of lead-free solder such as indium (In), a high phase transition temperature is more and more required. However, the currently developed eco-friendly lead-free piezoelectric body BF-BT system has excellent piezoelectric properties and a high phase transition temperature, but the Q _m value is less than 50, which is insufficient for practical application.

Therefore, in order for the actual material to be used as an application, it is required to develop a composition and technology that maintains the high phase transition temperature of the _{eco-friendly lead-free piezoelectric ceramics BiFeO 3} -BaTiO _{3 (BF-BT) system and has an excellent mechanical quality factor.} .

Korean Patent Publication No. 10-2010-0046634 (published on: 2010.05.07.) Korean Patent Laid-Open Publication No. 10-2015-0090853 (published on: August 6, 2015)

The technical problem to be solved by the present invention is to solve the low phase transition temperature ( T _c ) or thermal deterioration temperature ( T _d ), which is a problem with the existing lead-free piezoelectric ceramics, so that it can be directly applied to industrial fields such as ultrasonic sensors, resonators, humidifiers, etc. It is to provide a novel lead-free piezoelectric ceramics having an excellent mechanical quality factor ( Q _m ) and a high phase transition temperature and a method for manufacturing the same.

In order to solve the above technical problem, the present invention provides a lead-free piezoelectric ceramic represented by the following chemical formula:

[Formula]

(1-x)Bi _1.03 FeO ₃ -x(Ba _1-2y Li _y Al _y )TiO ₃

(In the above formula, 0.225 ≤ x ≤ 0.300, and 0.005 ≤ y ≤ 0.020).

Further, the present invention provides a lead-free piezoelectric ceramics, characterized in that it is represented by _{0.775Bi 1.03} FeO ₃ -0.225 (Ba _0.99 Li _0.005 Al _0.005 ) TiO _{3 .}

In addition, in the present invention, the mechanical quality factor ( Q _m ) is 253, the static voltage constant ( d ₃₃ ) is 58 pC/N, the electromechanical coupling coefficient ( K _p ) is 0.20, and the phase transition temperature ( T _C ) is 308 ° C. It provides a lead-free piezoelectric ceramics, characterized in that.

Furthermore, the present invention provides a method for manufacturing the lead-free piezoelectric ceramics, including (a) Bi ₂ O ₃ powder, Fe ₂ O ₃ powder, BaCO ₃ powder, TiO ₂ powder, Li ₂ CO ₃ powder, and Al ₂ O ₃ powder pulverizing and calcining the mixed powder to prepare a raw material powder; (b) sintering at 970 to 1000° C. after preparing a compact using the raw powder prepared in step (a); and (c) rapidly cooling the sintered body obtained in step (b); of ceramics A manufacturing method is provided.

In addition, the present invention is a lead-free piezoelectric, characterized in that the step (a) for producing the raw material powder is performed twice or more of ceramics A manufacturing method is provided.

In addition, the present invention provides a powder selected from _{Ga 2} O ₃ and Mn ₂ O ₃ in the mixed powder in step (a) to introduce gallium (Ga) and/or manganese (Mn) ions into the finally obtained lead-free piezoelectric ceramics. Lead-free piezoelectric, characterized in that it further comprises more than one type of metal oxide powder of ceramics A manufacturing method is provided.

In addition, the present invention is a lead-free piezoelectric, characterized in that further adding at least one metal oxide powder selected from CuO and MnO as a sintering aid to the mixed powder in step (a) of ceramics A manufacturing method is provided.

In addition, the present invention is a lead-free piezoelectric, characterized in that the air-cooling (air-cooling) the sintered body from the sintering temperature to room temperature in the step (c) of ceramics A manufacturing method is provided.

In addition, the present invention comprises the steps of forming an electrode on the surface of the rapidly cooled lead-free piezoelectric ceramics sintered body obtained by performing the above steps (a) to (c), and then calcining at a low temperature at 200 ° C., which is a temperature below the phase transition temperature, to prepare a capacitor structure. Lead-free piezoelectric, characterized in that it further comprises of ceramics A manufacturing method is provided.

And, in another aspect of the present invention, the eco-friendly lead-free piezoelectric Provided are ultrasonic devices including ceramics, ultrasonic sensors, ultrasonic cleaners, ultrasonic humidifiers, and the like.

The lead-free piezoelectric ceramics represented by (1-x)Bi _1.03 FeO ₃ -x(Ba _1-2y Li _y Al _y )TiO ₃ (0.225 ≤ x ≤ 0.300, 0.005 ≤ y ≤ 0.020) according to the present invention has excellent mechanical properties. It has a quality factor ( Q _m ), an electromechanical coupling factor ( k _P ), and a static piezoelectric constant ( d ₃₃ ), and at the same time has a high phase transition temperature of 300°C or higher, and various ultrasonic elements or devices such as ultrasonic sensors, ultrasonic cleaners, and ultrasonic humidifiers. It can be usefully used as a material for

In addition, in the method for manufacturing lead-free piezoelectric ceramics according to the present invention, the piezoelectric ceramics are manufactured by performing a quenching process after low-temperature sintering of the mixed raw material powder at a temperature of 970 to 1000 ℃, thereby reducing defect generation and the process It has the advantage of being able to shorten the time by more than 2 times compared to the conventional ceramic firing process, and also, because sintering is performed at low temperature, expensive electrode materials such as Pt (platinum) and Pd (palladium) are relatively inexpensive Ag (Silver), Ni (nickel), Cu (copper), etc. by mixing and using a metal has the advantage of co-firing (co-firing) the electrode and the ceramic.

1 is a disk-shaped (1-x)Bi _1.03 FeO ₃ -x (Ba _1-2y Li _y Al _y )TiO ₃ (x= 0.225, 0.250, 0.275, 0.300, y=0.005) A schematic diagram of a ceramic specimen.
2 is a composition of (1-x)Bi _1.03 FeO ₃ -x (Ba _1-2y Li _y Al _y )TiO ₃ (x=0.225, 0.250, 0.275, 0.300, y=0.005) prepared in Example 1 of the present application. It is a graph showing the results of X-ray diffraction pattern (XRD) analysis of piezoelectric ceramics.
3 is a graph showing a ferroelectric hysteresis curve and residual polarization measurement results of lead-free piezoelectric ceramics having a capacitor structure prepared in Example 2 of the present application.
4 is a graph showing the measurement result of the static piezoelectric constant (d ₃₃ ) of the lead-free piezoelectric ceramics of the capacitor structure prepared in Example 2 of the present application.
5 is a graph showing the electromechanical coupling coefficient (K _p ) and the mechanical quality factor ( Q _m ) of the lead-free piezoelectric ceramics of the capacitor structure prepared in Example 2 of the present application.
6 is a graph showing the measurement result of the dielectric constant according to the temperature of the lead-free piezoelectric ceramics of the capacitor structure prepared in Example 2 of the present application.

In describing the present invention, if it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the gist of the present invention, the detailed description thereof will be omitted.

Since the embodiment according to the concept of the present invention may have various changes and may have various forms, specific embodiments will be illustrated in the drawings and described in detail in the present specification or application. However, this is not intended to limit the embodiment according to the concept of the present invention with respect to a specific disclosed form, and should be understood to include all changes, equivalents or substitutes included in the spirit and scope of the present invention.

The terms used herein are used only to describe specific embodiments, and are not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises" or "have" are intended to designate that the described features, numbers, steps, operations, components, parts, or combinations thereof exist, and include one or more other features or numbers. , it is to be understood that it does not preclude the possibility of the presence or addition of steps, operations, components, parts, or combinations thereof.

Hereinafter, the present invention will be described in detail.

The present invention does not use lead, which is harmful to the environment and human body, of PZT-based piezoelectric ceramics, and maintains a high phase transition temperature, which is an advantage of _{BiFeO 3} -BaTiO _{3 (BF-BT)-based piezoelectric ceramics, and has an excellent mechanical quality factor.} As a new eco-friendly lead-free piezoelectric ceramics, a bismuth ferrite-barium titanate-based eco-friendly lead-free piezoelectric ceramics represented by the following chemical formula is provided.

[Formula]

(1-x)Bi _1.03 FeO ₃ -x(Ba _1-2y Li _y Al _y )TiO ₃

(In the above formula, 0.225 ≤ x ≤ 0.300, and 0.005 ≤ y ≤ 0.020).

An example of the lead-free piezoelectric ceramics is 0.775Bi _1.03 FeO ₃ -0.225 (Ba _0.99 Li _0.005 Al _0.005 ) TiO _{3 There} may be mentioned lead-free piezoelectric ceramics, characterized in that the lead-free piezoelectric ceramics have a mechanical quality factor ( Q _m ) is 253, the static voltage constant ( d ₃₃ ) is 58 pC / N, the electromechanical coupling coefficient ( K _p ) is 0.20, and the phase transition temperature ( T _C ) is 308 ° C. indicates physical properties.

On the other hand, the lead-free piezoelectric ceramics according to the present invention, (a) Bi ₂ O ₃ powder, Fe ₂ O ₃ powder, BaCO ₃ powder, TiO ₂ powder, Li ₂ CO ₃ powder and Al ₂ O ₃ A mixture comprising a powder pulverizing the powder and calcining to prepare a raw powder; (b) sintering at 970 to 1000° C. after preparing a compact using the raw powder prepared in step (a); and (c) rapidly cooling the sintered body obtained in step (b);

In this case, in step (a), a mixed raw material powder for manufacturing lead-free piezoelectric ceramics having the composition represented by the above formula is prepared.

First, according to the composition to be finally obtained, Bi ₂ O ₃ powder, Fe ₂ O ₃ powder, BaCO ₃ powder, TiO ₂ powder, Li ₂ CO ₃ powder, and Al ₂ O ₃ powder are weighed and mixed to prepare a mixed powder and pulverize the mixed powder.

At this time, as a method of pulverizing the mixed powder, zirconia (ZrO ₂ ) balls and ethanol are mixed together in a ball barrel made of Nalgene material, and a ball mill is performed using a milling machine to pulverize. A typical example is the ball milling method.

Then, the pulverized mixed powder is dried and calcined to remove organic matter, impurities or volatile gas contained in the mixed powder.

The calcination process of the mixed powder is preferably performed at 650 to 750° C. for 1 hour or more, and more preferably at 700° C. for 2 hours.

On the other hand, in order to improve the uniformity of the particle size distribution of the raw powder particles, this step (a) may be repeated two or more times as needed.

In addition, in this step (a), if necessary, one or more metal oxide powder selected from _{Ga 2} O ₃ and Mn ₂ O _{3 may be further added to the mixed powder.}

As described above, when Ga ₂ O ₃ and/or Mn ₂ O ₃ powder is added to the raw material powder, gallium (Ga) and/or manganese (Mn) ions are additionally doped into the lead-free piezoelectric ceramics to form the piezoelectricity of the lead-free piezoelectric ceramics. Further enhancement and/or control of properties may be sought.

In this case, Ga ₂ O ₃ and/or Al ₂ O ₃ powder is preferably added to the mixed powder in an amount of 0.5 to 3.0 mol% based on the total content of the mixed powder.

In addition, in this step (a), if necessary, as a sintering aid, one or more metal oxide powders selected from CuO and MnO may be further added to the mixed powder in an amount of 0.1 to 0.3 wt% based on the total content of the mixed powder.

Next, in step (b), the raw material powder is pressed to prepare a compact, and the produced compact is sintered.

The molded body may have various shapes and sizes, such as a disk shape, depending on the use and characteristics of the finally obtained lead-free piezoelectric ceramics.

The sintering process of the compact is preferably performed at 970 to 1000 °C for 1 to 5 hours.

Finally, in step (c), the lead-free piezoelectric ceramics sintered body obtained in step (b) is rapidly quenched, and mechanical properties of the lead-free piezoelectric ceramics can be improved through this step.

In this step, the sintered body may be rapidly cooled in various ways, for example, an air cooling process in which the sintered body, on which the sintering process is completed, is taken out from the electric furnace and rapidly cooled from the sintering temperature to room temperature in the atmosphere. In this case, the air cooling process may be performed within a short time of 5 to 30 minutes for the high-temperature sintered body to reach room temperature to maximize the rapid cooling effect of the sintered body.

_{The lead-free piezoelectric ceramics represented by (1-x)Bi 1.03} FeO ₃ -x(Ba _1-2y Li _y Al _y )TiO ₃ (0.225 ≤ x ≤ 0.300, 0.005 ≤ y ≤ 0.020) according to the present invention described in detail above is , excellent mechanical quality factor ( Q _m ), electromechanical coupling factor ( k _P ), and static piezoelectric constant ( d ₃₃ ) values, and at the same time has a high phase transition temperature of 300 ° C or higher, It can be usefully used as a material for an element or device.

Hereinafter, the present invention will be described in more detail by way of examples.

Embodiments according to the present specification may be modified in various other forms, and the scope of the present specification is not to be construed as being limited to the embodiments described below. The embodiments of the present specification are provided to more completely explain the present specification to those of ordinary skill in the art.

<Example 1>

1) Starting material

_{The present inventors prepared} a ceramic composition having a composition of (1-x)Bi _1.03 FeO ₃ -x(Ba 1-2y Li _y Al _y )TiO _{3 , Bi 2} O ₃ as a starting material according to the composition shown in Table 1 below. (99.9%), Fe ₂ O ₃ (99.9%), Li ₂ CO ₃ (99.99%) _, Al ₂ O ₃ (99.99%), TiO ₂ (99.9%), CaCO ₃ (99.9%) was prepared through a general solid-phase reaction method using a powder.

2) Composition of the sample

In _{(1-x) Bi 1.03 FeO} 3 -xBaTiO 3 The composition of the ceramic composition, x is selected, and the composition ratio of the raw material powder to be in a range of _{0.225 ~ 0.30, Bi 1.03 FeO 3} -BaTiO (Ba 1- solid solution of _{3 2y} Li _y Al _y ) In the TiO ₃ composition, y has a composition ratio of the raw material powders to be in the range of 0.005.

Detailed composition of the sample (unit: mole fraction) Example x y 1-1 0.225 0.005 1-2 0.250 0.005 1-3 0.275 0.005 1-4 0.300 0.005

3) Ceramic manufacturing

After mixing the starting material with ethanol, weighing a stabilized zirconia (YSZ) ball with a diameter of 10 mm and excellent mechanical strength at a weight ratio of 1:6, put it in a Nalgene bottle, and then ball milling for 12 hours to obtain a powder. Mix and grind. After ball milling, the balls were removed using a sieve, and the raw material powder mixed with ethanol was dried in an oven at 90° C., and the dried powder was calcined at 700° C. in an air atmosphere for 2 hours. Preferably, in order to increase the homogeneity of the final powder particles, the ball milling, drying, and calcining processes were repeated twice each to obtain a final powder.

4) molding

Poly Vinyl Alcohol (PVA) was added and mixed to the final powder as a binder for molding and sieved through a 150 μm sieve. The sieved powder was produced in the form of a disk having a diameter of 10 mm and a thickness of 1 mm by applying a pressure of 250 MPa using a single screw press molding machine.

5) sintering process

The prepared specimen was placed on an alumina plate and charged into a powder with the same composition to prevent the volatilization of Bi ions and direct reaction between the alumina plate and the specimen. A disk-shaped bulk ceramic is placed in a box-type electric furnace, and in consideration of sufficient volatilization of PVA, which is known to have a melting point of 228 ℃, the binder is maintained at 300 ℃ for 1 hour, and then each composition is adjusted to 970 ~ 1000 ℃ at a temperature increase rate of 10 ℃/min. It was sintered at temperature for 3 hours.

6) Rapid cooling process

According to the thermodynamic study of BiFeO ₃ (BF)-based piezoelectric ceramics, in the temperature range of ^{447 o} C to 767 ^o _{C, Bi 25} FeO ₃₉ and Bi ₂ Fe ₄ O ₉ were Since it is known to have a fairly unstable phase such as a lack of Bi or a lack of Fe, in order to avoid such an unstable phase, the ceramic was cooled to room temperature by using a rapid cooling process rather than a natural cooling method immediately after the sintering temperature was finished. .

7) Surface polishing and removal of impurities

After finishing the final sintering process, the ceramic specimen obtained through the rapid cooling process was polished to a thickness of 0.4 mm using SiC abrasive paper on both sides of the surface, and finally surface residual stress was reduced as much as possible using #4000 abrasive paper. The polished ceramic was dried for 30 minutes in a dryer at a temperature of ^{90 o} C after removing residual impurities through an ultrasonic cleaner.

<Example 2>

In order to measure the electrical properties, the ceramics prepared in Example 1 were first coated with a platinum ion stuffer (Pt Ion-Sputter). After the secondary coating using Silver (silver)-Palladium (palladium)-paste, it was dried for 60 minutes in a dryer at ^{200 o C.} In order to obtain a uniform electrode surface, the surface was polished using abrasive paper having a surface roughness of 1 micrometer, and finally, a ceramic having a capacitor structure as shown in FIG. 1 was manufactured.

<Experimental example>

1) X-ray diffraction measurement

In order to analyze the structure of the polished bulk ceramic, it was measured using an XRD measuring device (Rigaku, MiniFlex II) having a CuKα (λK _a1 =1.540562 Å, λK _{a2 =1.544398 Å) wavelength and is shown in FIG. 2 .}

As a result, the perovskite structure of a single structure without an impurity phase is well represented in all compositions, and the (111) and (1 1 ^{1) picks observed around 39 o} move to a lower angle as the amount of x increases. And, it can be seen that the x = 0.300 sample in which a relatively large amount of BaTiO _{3 is dissolved has the lowest 2θ value.} In addition, it can be seen that the x=0.300 sample is not clearly distinguished from the two picks (111) and (1 1 1) compared to other samples. This is because BaTiO ₃ has relatively soft ferroelectricity compared to BiFeO ₃ and has a large lattice constant.

2) Measurement of ferroelectric hysteresis curve

3 is a ferroelectric hysteresis curve measuring device (RT6000 HVS, Radiant) to measure the polarization-electric field ( P - E ) hysteresis curve of the ceramic sample, and then connecting the + and - poles to both ends of the ceramic electrode This is the result of measuring the P - E hysteresis curve using a 10 Hz triangular wave in an electric field of 80 kV/cm at room temperature after putting it in a silicone oil container.

As a result, it was confirmed that the coercive electric field ( E _{c ) decreased as the solid solution amount of BaTiO 3} , which had relatively soft ferroelectricity, _{increased compared to that of the imitation BiFeO 3} , while the value of the residual polarization ( P _r ) increased. became

These results show that in most BNT, BKT, and KNN-based lead-free piezoelectric ceramics, hard doping or acceptor doping was performed on the lead-free piezoelectric material based on defect chemistry to improve the mechanical quality factor, and the ferroelectric hysteresis curve was obtained. It was confirmed to have a ferroelectric hysteresis curve close to an ideal shape, which is different from having artificially asymmetry, double hysteresis loop, or antiferroelectrics hysteresis curves.

3) Polarization treatment and static piezoelectric constant measurement

FIG. 4 shows the + and - poles connected to both ends of the ceramic electrode using a DC high voltage device (248, Keithley) to align the ferroelectric regions of the ceramic sample having the electrode-treated capacitor structure, and then placed in a silicone oil container. After that, the polarization treatment was performed by maintaining it in an electric field of 80 kV/cm at room temperature for 30 minutes. Then, using a static piezoelectric measuring device (piezo- d ₃₃ -meter, ZJ-6B, IACAS) was measured using a force of 0.25 N and a frequency of 110 Hz. As a result, as the solid solution _{amount of BaTiO 3} increased, the static piezoelectric constant increased [x=0.225 ( d ₃₃ = 62 pC/N), x=0.25 ( d ₃₃ = 112 pC/N)], and the highest at x=0.275 It _{has a value of d 33} = 212 pC/N, and it was confirmed that it was lowered again from x = 0.300 to d _{33 = 195 pC/N.}

4) Mechanical quality factor and electromechanical coupling factor

Using an impedance analyzer (HP4194A, Agilent) for a ceramic specimen with sufficiently aligned polarization, the electromechanical coupling coefficient ( k _p ) and the mechanical quality factor ( Q _m ) are calculated using the following Equations 1 and 2 shown in

Equation 1)

Equation 2)

(Where, f _r is the resonant frequency (Hz), f _a is the antiresonant frequency (Hz), Z _r is the resonant impedance (Resonant resistance, Ω), C is the static capacitance (F) )

As a result, it was confirmed that it had the highest machine quality factor, Q _{m = 253, at x = 0.225.} It can be seen that this has a significantly improved value than the value of Q _m = 33 known in the eco-friendly lead-free BiFeO ₃ -BaTiO _{3 piezoelectric ceramics.} In addition, it was found that the electromechanical coupling coefficient k _p = 0.20 had a fairly good value.

5) Measurement of dielectric properties and phase transition temperature according to temperature

_{The dielectric constant (ε r)} in the frequency range of 10 kHz while heating and cooling the ^{electrode-treated bulk ceramic at a rate of 1 o} C/min from 30 ℃ to 400 ℃ using an impedance measuring device (HP4194, Agilent). ) was measured, and based on this , the ferroelectric phase transition temperature ( T _c ) or thermal degradation temperature ( T _d ) for the x=0.225 composition having the highest Q _m value and the x=0.275 composition having the highest static piezoelectric constant in FIG. 6 . was shown.

As a result, x= 0.225 and 0.275, which are the compositions with the best piezoelectric properties and mechanical quality factor, both have a phase transition temperature ( T _c ) or thermal deterioration temperature ( T _d ) of 300 ° C or higher, which is a typical lead-free piezoelectric material known in the past. It has high temperature stability compared to the room temperature or the temperature below ~200 ℃ in the composition of BNT, BKT, and KNN.

The present invention is not limited to the above embodiments, but can be manufactured in various different forms, and those of ordinary skill in the art to which the present invention pertains can take other specific forms without changing the technical spirit or essential features of the present invention. It will be understood that it can be implemented as Therefore, it should be understood that the embodiments described above are illustrative in all respects and not restrictive.

100: lead-free piezoelectric ceramics specimen having a capacitor structure
200: disk-shaped lead-free piezoelectric ceramics specimen
300: silver: palladium mixed electrode

Claims (11)

Lead-free piezoelectric ceramics represented by the formula:
[Formula]
(1-x)Bi _1.03 FeO ₃ -x(Ba _1-2y Li _y Al _y )TiO ₃
(In the above formula, 0.225 ≤ x ≤ 0.300, and 0.005 ≤ y ≤ 0.020). According to claim 1,
0.775Bi _1.03 FeO ₃ -0.225 (Ba _0.99 Li _0.005 Al _0.005 ) TiO ₃ Lead-free piezoelectric ceramics, characterized in that it is represented. 3. The method of claim 2,
The mechanical quality factor ( Q _m ) is 253, the static piezoelectric constant ( d ₃₃ ) is 58 pC/N, the electromechanical coupling coefficient ( K _p ) is 0.20, and the phase transition temperature ( T _C ) is 308 ° C. Lead-free piezoelectric ceramics. (a) Bi ₂ O ₃ powder, Fe ₂ O ₃ powder, BaCO ₃ powder, TiO ₂ powder, Li ₂ CO ₃ powder and Al ₂ O ₃ powder mixed powder containing the powder is pulverized and calcined (calcination) to obtain a raw material powder manufacturing;
(b) sintering at 970 to 1000° C. after preparing a compact using the raw powder prepared in step (a); and
(c) rapidly cooling the sintered body obtained in step (b); of ceramics manufacturing method. 5. The method of claim 4,
Lead-free piezoelectric, characterized in that the process of manufacturing the raw material powder in step (a) is performed twice or more of ceramics manufacturing method. 5. The method of claim 4,
In the step (a), the mixed powder is lead-free piezoelectric, characterized in that it further comprises one or more metal oxide powder selected _{from Ga 2} O ₃ and Mn ₂ O ₃ of ceramics manufacturing method. 5. The method of claim 4,
In the step (a), the mixed powder further comprises at least one metal oxide powder selected from CuO and MnO as a sintering aid. of ceramics manufacturing method. 5. The method of claim 4,
Lead-free piezoelectric, characterized in that air-cooling the sintered body from the sintering temperature to room temperature in step (c) of ceramics manufacturing method. 5. The method of claim 4,
After forming an electrode on the surface of the rapidly cooled lead-free piezoelectric ceramics sintered body, the method further comprises the step of manufacturing a capacitor structure by sintering at a temperature below the phase transition temperature of 200° C. of ceramics manufacturing method. The lead-free piezoelectric of any one of claims 1 to 3 An ultrasonic device comprising ceramics. 11. The method of claim 10,
The ultrasonic device, characterized in that the ultrasonic sensor, ultrasonic cleaner or ultrasonic humidifier.

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