KR101685097B1 - Composite bismuth-based lead-free piezoelectric ceramics and actuator using the same - Google Patents

Abstract

The present invention relates to composite bismuth-based lead-free piezoelectric ceramics, an actuator including the same, and a method for manufacturing the composite bismuth-based lead-free piezoelectric ceramics, and more specifically, to composite bismuth-based lead-free piezoelectric ceramics which has excellent electric field induced strain (EFIS) in a low electric field, an actuator including the same, and a method for manufacturing the composite bismuth-based lead-free piezoelectric ceramics. According to one embodiment of the present invention, the composite bismuth-based lead-free piezoelectric ceramics are a (Bi, Na)TiO_3-SrTiO_3-based solid solution where SrTiO_3 is added to a (Bi, Na)TiO_3-based matrix while a part of (Bi, Na)TiO_3 in the (Bi, Na)TiO_3-SrTiO_3-based solid solution is substituted with KNbO_3 having a pseudo-cubic structure, and have a perovskite crystal structure.

Description

TECHNICAL FIELD [0001] The present invention relates to a composite bismuth-based lead-free piezoelectric ceramics and an actuator including the same,

The present invention relates to a composite bismuth-based lead-free piezoelectric ceramics, an actuator including the same, and a method for manufacturing a composite bismuth lead-free piezoelectric ceramic. More particularly, the present invention relates to a composite bismuth alloy having excellent electric field induced strain (EFIS) The present invention relates to a lead-free piezoelectric ceramics, an actuator including the same, and a method for manufacturing a composite bismuth-based lead-free piezoelectric ceramics.

Piezoelectric ceramics is a device in which mechanical deformation occurs when a voltage is applied and an external electric field is applied. It converts mechanical energy into electrical energy and electrical energy into mechanical vibration energy. It is a possible material. It is applied to the acceleration sensor by using the principle that can convert vibration into electric energy. It is applied to pickup of record disc, microphone, speaker, buzzer etc. by using the principle of converting the sound of the audible area to electric energy. And is used as a device. In addition, since ultrasonic waves can be transmitted and received, it is used as a probe tip and a sonar of an ultrasonic sensor. If a force or pressure is applied from the outside, a high-voltage spark can be generated. It is applied to transformer. Other applications include ceramic filters, ultrasonic cleaners, ultrasonic machines, ultrasonic welding machines, ultrasonic humidifiers, etc. Piezoelectric materials, which are components used in smart information communication devices, Electro-mechanical system) and an actuator module mounted on a camera / microscope.

Pb (Zr, Ti) O ₃ (hereinafter referred to as PZT) is generally used because it has excellent performance required in the industry, such as high electrical properties including high piezoelectric coefficient (d ₃₃ ) There is a problem that it is harmful to the human body and causes environmental problems. Therefore, in recent years, lead-free piezoelectric ceramics which do not use lead have been studied.

Substituents for the PZT system all have a perovskite structure, the perovskite structure can be denoted as ABO ₃ . In order to have a stable perovskite structure, the sum of the atomic valences of the A site ion and the B site ion should be 6 ⁺ , and the size and mass of the ions are also important factors for determining the crystal structure and physical properties.

As a substitute for the PZT system, a bismuth system containing heavy bismuth (Bi) elements such as Pb in A site is being studied. Among them, Ti ⁺ 4 ⁺ element is located in B site and Bi ⁺ the (Bi, Na) TiO ₃ (hereinafter BNT) a high remanent polarization as a ferroelectric material at room temperature (P _r = 38μC / ㎠) characteristic and a high [Na ⁺ for periods according Add 2 ⁺ the element and a site contains at the same rate Phase transition temperature (T _c = 320 ° C), it is receiving the spotlight as a next generation lead-free piezoelectric material that can be used as a component material for mobile smart information appliances and the like. However, BNT has a disadvantage that it has an electric field induced strain (EFIS), a piezoelectric property (d ₃₃ ) and a high coercive electric field value which are too low as compared with a piezoelectric material based on PZT.

Therefore, a major issue of the bismuth lead-free piezoelectric ceramics is that the practical use of the discovered large strain is that the intensity of the electric field required to induce the large strain and consequently the hysteresis involved is too large, Although it is not a problem if only the on / off type actuator application is considered, the fact that the applied voltage is high is ultimately problematic regardless of the application.

The conventional bismuth lead-free piezoelectric ceramics has a problem that the electric field organic strain is gradually improved, but the electric field required for inducing the large strain is 5 kV / mm or more and the applied voltage is high.

Korean Patent Registration No. 10-1306472

The present invention provides a composite bismuth lead-free piezoelectric ceramics having properties such as a low electric field value and a high electric field organic strain in a low electric field and being harmless to a human body and applying this to an actuator, An actuator including a bismuth-based lead-free piezoelectric ceramics is provided.

A complex of bismuth-based lead-free piezoelectric ceramic according to an embodiment of the present invention (Bi, Na) TiO ₃ based matrix is added to the SrTiO _{3 (Bi, Na) TiO 3 -SrTiO} 3 based on the solid solution (Bi, Na) TiO ₃ is replaced with KNbO ₃ having a pseudo-cubic structure, and may have a perovskite crystal structure.

The composite bismuth lead-free piezoelectric ceramics may have a composition of (1-x) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -KNbO ₃ wherein x is 0.22? X? 0.25.

The composite bismuth-based lead-free piezoelectric ceramics may have a composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ wherein y is 0.0075 ≤ y ≤ 0.0125.

The composite bismuth lead-free piezoelectric ceramics may have a maximum strain of 0.15 to 0.35% in an electric field of 3 to 4 kV / mm.

The composite bismuth lead-free piezoelectric ceramics may have a normalization strain (S _Max / E _Max ) of 500 to 800 pm / V at an electric field of 3 to 4 kV / mm.

The composite bismuth lead-free piezoelectric ceramics may have an absolute value of negative maximum strain of 0 to 0.05% at an electric field of 3 to 4 kV / mm.

In the composite bismuth lead-free piezoelectric ceramics, a ferroelectric phase and a nonpolar phase can coexist.

The actuator according to another embodiment of the present invention is a composite bismuth lead-free piezoelectric ceramics according to an embodiment of the present invention; And an electrode for providing an electrical signal to the composite bismuth-based lead-free piezoelectric ceramics.

In the composite bismuth lead-free piezoelectric ceramics, a ferroelectric phase and a non-polar phase coexist, and when an electric field is applied through the electrode, a phase transition from a nonpolar phase to a ferroelectric phase may occur.

Another embodiment compound of bismuth-based lead-free piezoelectric ceramic manufacturing method according to the present invention _{(Bi, Na) TiO 3 -SrTiO} 3 forming composition Bi, Na, Sr, an oxide of Ti powder and the (Bi, Na) TiO ₃ is Mixing the oxide powder of K, Nb constituting the substituted KNbO ₃ ; Calcining the mixed powder; Pressing the calcined powder to form a formed body; And sintering the formed body to form a sintered body having a perovskite crystal structure.

The sintered body is (1-xy) [(Bi , Na) TiO 3] -xSrTiO 3 -yKNbO 3 may have a composition of (here, wherein x is 0.22 ≤ x ≤ 0.25, said y is 0.0075 ≤ y ≤ 0.0125) .

The ferroelectric phase and the nonpolar phase may coexist in the sintered body.

Complex of bismuth-based lead-free piezoelectric ceramic according to the present invention (Bi, Na) TiO ₃ type of matrix is added to the SrTiO _{3 (Bi, Na) TiO 3 -SrTiO} 3 solid solution based on (Bi, Na) TiO ₃ the pseudo cubic crystal ( by some substituted with KNbO ₃ having a pseudo-cubic) structure, can lead to local distortions of the lattice caused the tragedy aqueous phase (Non-polar phase). Accordingly, the composite bismuth-based lead-free piezoelectric ceramics of the present invention can have a high electric field induced strain (EFIS) even at a low electric field, and can have a low anti-electric field value.

And, due to the phase transition behavior according to the nonpolar electric field, it is possible to achieve a large strain in a low electric field, and thus a high S _max / E _max (normalized strain, d ₃₃ ^* ) value in a low electric field generally required in an actuator The piezoelectric actuator module can be expected to have a higher electrical characteristic than a low applied voltage.

Further, unlike the conventional Pb (Zr, Ti) O ₃ (hereinafter referred to as PZT) which is harmful to the human body and causes environmental pollution, the present invention provides a piezoelectric ceramics material of Bi- Lead-free piezoelectric ceramics can be obtained.

The composite bismuth-based piezoelectric ceramics according to the present invention can be used in a solid-phase reaction method. The production process is simple and easy to produce. Mass production is possible, thereby reducing production costs.

1 is a hysteresis curve graph showing unipolar electric field organic strain of conventional bismuth piezoelectric ceramics.
2 is a graph _{showing the} relationship between the bipolar electric field of piezoelectric ceramics for each composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ (y = 0, 0.01, 0.02) Hysteresis curve graph showing organic strain.
3 is a graph showing the polarization characteristics of piezoelectric ceramics for each composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ (y = 0, 0.01, 0.02) according to an embodiment of the present invention. Hysteresis curve graph.
4 is a graph _{showing the} relationship between the composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -yKNbO ₃ (y = 0.01) according to an embodiment of the present invention, Hysteresis curve graph showing strain.
5 is a flowchart showing a method of manufacturing a composite bismuth-based lead-free piezoelectric ceramics according to another embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. It will be apparent to those skilled in the art that the present invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, It is provided to let you know. In the description, the same components are denoted by the same reference numerals, and the drawings are partially exaggerated in size to accurately describe the embodiments of the present invention, and the same reference numerals denote the same elements in the drawings.

A complex of bismuth-based lead-free piezoelectric ceramic according to an embodiment of the present invention (Bi, Na) TiO ₃ based matrix is added to the SrTiO _{3 (Bi, Na) TiO 3 -SrTiO} 3 based on the solid solution (Bi, Na) TiO ₃ is replaced with KNbO ₃ having a pseudo-cubic structure, and may have a perovskite crystal structure.

(Bi, Na) TiO ₃ (hereinafter BNT) based lead-free (Pb-free) piezoelectric ceramic is _{Pb (Zr, Ti) O 3} ( hereinafter PZT) based on lead-based piezoelectric ceramic and similarly ABO ₃ type perovskite ( Perovskite structure, Ti ^{4 +} is located in B-site, and Bi ^{3 +} element and Na ^{1 +} element are mixed in A-site, resulting in a bivalent element Material. These materials cause electrical polarization in the Z-axis direction of the crystal structure due to the external electric field and Ti ^{4 +} ions located at the B-site cause mechanical deformation as a result of the polarization. However, BNT materials have a high Curie temperature (T _c ), while the antioxidant system is too high.

In order to solve these problems, attempts have been made to change the properties of the extreme nano-domains using various dopants.

FIG. 1 is a hysteresis curve graph showing unipolar electric field organic strain of conventional bismuth piezoelectric ceramics, and is a hysteresis curve graph showing unipolar electric field organic strain of BNKT-LA, BNKT-BF and BNT-ST piezoelectric ceramics.

Referring to Figure 1, [Bi (Na, K )] TiO 3 -LaAlO 3 ( hereinafter BNKT-LA), [Bi ( Na, K)] TiO 3 -BiFeO 3 ( hereinafter BNKT-BF) and [(Bi, Na) TiO ₃ ] -SrTiO ₃ (hereinafter referred to as BNT-ST) piezoelectric ceramics exhibits a high electric field induced strain (EFIS).

As described above, the bismuth-based piezoelectric ceramics based on BNT is characterized by exhibiting high electric field organic strain. The high electric field organic strain is caused by the phase transition due to the electric field. The compositions such as BNKT-LA and BNKT-BF exhibit a high electric field organic strain, but the electric field required for inducing a high strain is high. To overcome this problem, a BNT-ST system was developed by adding SrTiO ₃ (ST) with a cubic structure as a dopant to the BNT-based matrix.

1, the hysteresis phenomenon of BNKT-LA and BNKT-BF is large and shows a low strain in a low electric field. However, BNT-ST saturates at about 2.5 kV / mm, It can be confirmed that the strain exhibits a high strain in a low electric field. The BNT-ST system can be represented by a composition of (1-x) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ (hereinafter referred to as (1-x) BNT-x ST) And the electric field organic strain can be improved.

Since the ratio of ferroelectric phase to non-polar phase can be controlled to show a high electric field organic strain in a low electric field, it is difficult to control the ratio of ferroelectric phase to non-polar phase only by the ratio of ST, The non-polar phase takes a higher proportion of the ferroelectric phase than the non-polar phase, so that a high electric field is required for the phase transition to the ferroelectric phase, thereby reducing the strain induced by the electric field, Can not be represented.

Accordingly, in the present invention, in order to further improve the electric field organic strain and ensure higher electric field organic strain characteristics in a low electric field, a part of BNT is replaced with KNbO ₃ (hereinafter referred to as KN) in the BNT- , Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ composition. Here, (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ may form a solid solution and may have a perovskite crystal structure. That is, by replacing pseudo-cubic KNbO ₃ (KN), which is known to exhibit a high electric field organic strain, with some BNT sites by forming a BNT and a morphotropic phase boundary (MPB) in the BNT-ST system, A high electric field organic strain can be ensured in a low electric field.

The composite bismuth lead-free piezoelectric ceramics according to the present invention may have a composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ wherein x is 0.22? X? 0.25. The complex of bismuth-based lead-free piezoelectric ceramic is (1-xy) [(Bi , Na) TiO 3] may have a composition of -xSrTiO ₃ -yKNbO _3, it becomes x is greater than 0.25, the non-polar phase is too greater than the ferroelectric non-polar phase ferroelectric Phase shifts to the phase of paraelectric phase. When x is smaller than 0.22, the ferroelectric phase becomes larger than the nonpolar phase, so that the phase transition field can be lowered. However, when the ferroelectric phase is too much larger than the trapezoidal phase Therefore, the maximum strain (S _Max ) also becomes low.

In detail, the BNT has a perovskite-type surface roughness (R3c) structure at room temperature and ST is also a perovskite type and has a perovskite type cubic structure at room temperature. When the ferroelectric BNT having a uniform planar structure is replaced with 23 to 27 mol% of the cubic structure ST, a high electric field organic strain is exhibited.

Among these BNT-ST systems, 0.74 (Bi, Na) TiO ₃ -0.26SrTiO ₃ (hereinafter referred to as 74BNT-26ST) system with x of 0.26 is the relaxation type ferroelectric and has the highest maximum strain (S _max ) , Which shows a high electric field organic strain at an electric field higher than 4 ㎸ / ㎜, but it can not saturate at an electric field of 4 ㎸ / ㎜ or less. Therefore, the field organic strain is not good at a field of 4 ㎸ / ㎜ or less. These 74BNT-26ST piezoelectric ceramics show electric field organic strain similar to that of commercial PZT at an electric field higher than 4 ㎸ / ㎜, but it does not reach the field organic strain of commercial PZT at an electric field of 4 ㎸ / ㎜ or less.

More precisely, in the case of 74BNT-26ST with x = 0.26, the lattice distortion is large due to ST, and the non-polar phase occupies a larger proportion than the ferroelectric phase, so a non-polar phase requires a high electric field to phase- Further, even if a part of BNT is replaced with KN, the distortion of the lattice is further increased, and the strain is transferred to the upper phase, and the field organic strain value saturated in the low electric field can not be obtained. That is, in the 74BNT-26ST system, due to the substitution of KN, the proper ratio of ferroelectric phase and nonpolar phase can not be derived, so that the field organic strain value saturating in a low electric field can not be obtained.

When x is larger than 0.26, the distortion of the lattice is further increased by ST, and the strain induced by the electric field is also decreased. That is, when x is larger than 0.26, the maximum strain (S _max ) becomes lower than 74BNT-26ST, and the field organic strain in the low electric field becomes lower, so that the field organic strain value saturated in the low electric field can not be obtained.

Further, since the nonpolar phase occupies a relatively larger proportion than the ferroelectric phase when x is between 0.25 and 0.26, the electric field necessary for the phase transition from the nonpolar phase to the ferroelectric phase becomes higher as the portion of the BNT is substituted with the KN, The organic strain value can not be obtained.

Therefore, if x is larger than 0.25, the appropriate ratio of ferroelectric phase and nonpolar phase can not be derived through the substitution of KN in the (1-x) BNT-xST system, so that the field organic strain value saturating in the low electric field can not be obtained.

And x is when smaller than 0.22 but is turned ferroelectric phase more than tragedy aqueous lower phase transfer field, since the ferroelectric phase is too large for tragedy constellation lower maximum strain the maximum strain (S _Max) (S _Max) of commercial PZT It will not reach the maximum strain.

Meanwhile, in one embodiment of the present invention, the composition of 0.77 (Bi, Na) TiO ₃ -0.23 SrTiO ₃ (hereinafter referred to as 77BNT-23ST) having x of 0.23, which is characterized by rapid saturation at a low electric field, have. And, by substituting the pseudocubic KN, which is known to exhibit high field organic strain, to some BNT sites, BNT and morphotropic phase system are formed to further improve the field organic strain and high field organic strain can be secured in the low electric field.

2 is a graph _{showing the} relationship between the bipolar electric field of piezoelectric ceramics for each composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ (y = 0, 0.01, 0.02) Fig. 2 (a) is a hysteresis curve showing the bipolar electric field organic strain when y = 0, and Fig. 2 (b) is a hysteresis curve graph showing the bipolar electric field organic strain And FIG. 2 (c) is a hysteresis curve graph showing bipolar electric field organic strain when y = 0.02.

Table 1 (1-xy) according to one embodiment of the present invention _{[(Bi, Na) TiO 3} ] -xSrTiO 3 -yKNbO 3 (y = 0, 0.0025, 0.005, 0.0075, 0.01, 0.0125, 0.015, 0.02) (S _max ) of each composition for each composition.

Field y = 0 y = 0.0025 y = 0.005 y = 0.0075 y = 0.01 y = 0.0125 y = 0.015 y = 0.02 3 kV / mm 0.10% 0.11% 0.14% 0.17% 0.23% 0.15% 0.09% 0.03% 4 kV / mm 0.13% 0.16% 0.23% 0.27% 0.31% 0.21% 0.14% 0.07% 5 kV / mm 0.16% 0.18% 0.27% 0.29% 0.34% 0.23% 0.16% 0.11%

Referring to FIG. 2 and Table 1, the (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -yKNbO ₃ system where x is 0.22 ≤ x ≤ 0.26 indicates that even though a part of BNT is not substituted with KN That is, even when y = 0, it can be confirmed that saturation occurs at a low electric field of 3 kV / mm. However, the maximum strain (S _max ) is low when a part of the BNT is substituted with KN and y = 0 (FIG. 2a), and a negative strain is exhibited in the electric field organic strain (SE) graph.

When a piezoelectric ceramics is applied to an actuator, only a positive strain is used. In addition, negative strain may be removed to increase positive strain.

In this case, saturation does not occur at an electric field of 3 kV / mm when y = 0.01 (FIG. 2B). However, since a part of BNT is substituted with KN, negative strain is removed and positive strain is increased, The maximum strain (S _Max ) in the electric field of the magnetic field can be expressed. Accordingly, the conventional bismuth piezoelectric ceramics exhibited a maximum strain (S _Max ) lower than 0.1% at a low electric field of 3 kV / mm. However, the composite bismuth piezoelectric ceramics of the present invention exhibited a low electric field of 3 kV / And a maximum strain (S _Max ) of 0.2% or more, which is more than two times higher than that of the sample.

In addition, y = 0.01 (Fig. 2b) and the saturation in the 4 ㎸ / ㎜ when the number of up and exhibit a high maximum strain (S _Max), thus high up byeonryul in the low electric field of 3 to 4 ㎸ / ㎜ (S _Max ) Can be obtained.

On the other hand, in an electric field of less than 3 kV / mm (for example, an electric field of 1 to 2 kV / mm), the electric field is not sufficient and it is difficult to secure the maximum strain (S _max ) It is difficult.

3 is a graph showing the polarization characteristics of piezoelectric ceramics for each composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ (y = 0, 0.01, 0.02) according to an embodiment of the present invention. FIG. 3 (a) is a hysteresis curve showing the polarization characteristic when y = 0, and FIG. 3 (b) is a hysteresis curve graph showing polarization characteristics when y = 0.01, 3 (c) is a hysteresis curve graph showing the polarization characteristic in the case of y = 0.02.

3, when y = 0 (FIG. 3A) in which a part of BNT is not substituted with KN in the (1-x) BNT-xST system, the remanent polarization and antiferromagnetism in the electric field polarization characteristic (1-x) BNT-xST (see FIG. 3A). In the PE graph of FIG. 3A, the residual polarization and the high-coercive shape appear in the SE graph of FIG. 2A, For example, x = 0.23), the ferroelectricity is high. This ferroelectricity can lower the phase transition field, but the negative strain is caused and the maximum strain (S _max ) is also lowered.

A high amount of electric field organic strain appears when a ferroelectric phase and a nonpolar phase coexist. The ferroelectric phase exhibits a negative strain and a low positive strain. However, when a ferroelectric phase and a nonpolar phase coexist, , So that the positive strain can be increased as the negative strain is removed. That is, in the S-E graph, the S-E hysteresis curve is raised as a whole, and the minimum value of the field organic strain is increased. When a piezoelectric ceramics is applied to an actuator, negative strain may be eliminated because only a positive strain is used. Accordingly, the composite bismuth lead-free piezoelectric ceramics according to the present invention may have an absolute value of negative maximum strain of 0 to 0.05%. The composite bismuth lead-free piezoelectric ceramics may have an absolute value of a negative maximum strain of 0 to 0.05% at an electric field (or a low electric field) of 3 to 4 kV / mm.

In order to make the ferroelectric phase and the nonpolar phase coexist, if the position of the BNT in the ferroelectric phase (1-x) BNT-xST is partially replaced with the perovskite structure and the pseudo cubic KN, the localized lattice distortion The nonpolar phase is induced.

Therefore, the position of the BNT having the perovskite crystal structure of ABO _{3 in} the ferroelectric phase (1-x) BNT-xST (for example, x = 0.23) is partially replaced with the perovskite structure and the pseudocubic KN It is possible to induce distortion of the lattice locally to induce the nonpolar image. Accordingly, the ferroelectric phase and the non-polar phase can coexist in the composite bismuth lead-free piezoelectric ceramics according to the present invention.

As shown in FIG. 2 and Table 1, the negative strain is decreased and the maximum strain (S _max ) is increased as the ratio of the portion of the BNT to the KN is increased (that is, y is 0.01 or 0.02) Of the total number of employees. In the PE graphs of FIGS. 3B and 3C, it can be seen that as the ratio of the portion of BNT to KN is increased, the residual polarization and the antiferromagnetic field are decreased. That is, as the KN is partially substituted in the BNT site, the local lattice distortion occurs, and the ferroelectric phase and the nonpolar phase coexist. As the ratio of the nonpolar phase increases, the residual polarization and the electrostatic field decrease, and the positive strain increases. However, at y = 0.02, the ratio of the nonpolar phase is excessively increased, and the strain induced by the electric field decreases due to the excessive lattice distortion. Here, the generation (or ratio) of the nonpolar phase can be deduced from the reduced remanent polarization (P _Rem ) value in the PE hysteresis curve graph. If the nonpolar phase is transformed into ferroelectric phase by applying an electric field, There is a characteristic that the phase transition occurs again. Due to the phase transition behavior depending on the electric field of the nonpolar phase, high electric field organic strain characteristics can be exhibited. As the ratio of the nonpolar phase increases, the electric field required to cause the phase transition increases.

Table 2 summarizes (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ (y = 0, 0.0025, 0.005, 0.0075, 0.01, 0.0125, 0.015, 0.02) according to one embodiment of the present invention. Lt; 2 > / mm < 2 >

at 3 kV / mm y = 0 y = 0.0025 y = 0.005 y = 0.0075 y = 0.01 y = 0.0125 y = 0.015 y = 0.02 E _c (kV / mm) 1.45 1.37 1.21 1.12 0.91 0.79 0.68 0.45 P _Max (μC / cm 2) 32.91 32.99 22.64 27.85 26.08 25.62 22.74 12.91 P _Rem (μC / cm 2) 26.85 22.21 9.65 10.03 5.37 5.86 5.04 2.32 (P _Rem / P _Max )
* 100 (%) 81.57 67.31 42.62 36.01 20.59 22.87 22.16 17.97 S _Max (%) 0.10 0.11 0.14 0.17 0.23 0.15 0.09 0.03 S _Max / E _Max 333 366 466 566 766 500 300 100

Table 3 shows the results of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ (y = 0, 0.0025, 0.005, 0.0075, 0.01, 0.0125, 0.015, 0.02) according to an embodiment of the present invention. In the electric field of 4 kV / mm.

at 4 kV / mm y = 0 y = 0.0025 y = 0.005 y = 0.0075 y = 0.01 y = 0.0125 y = 0.015 y = 0.02 E _c (kV / mm) 1.43 1.34 1.21 1.12 0.93 0.79 0.68 0.55 P _Max (μC / cm 2) 35.09 34.14 31.98 30.34 35.67 30.35 25.23 18.31 P _Rem (μC / cm 2) 28.45 22.69 12.98 10.64 8.61 6.78 5.43 2.97 (P _Rem / P _Max )
* 100 (%) 81.07 66.47 40.59 35.07 24.13 22.34 21.52 16.22 S _Max (%) 0.13 0.16 0.23 0.27 0.31 0.21 0.14 0.07 S _Max / E _Max 325 400 575 675 775 525 350 175

Referring to Tables 2 and 3, the maximum strain (S _Max ) increases as y increases to 0.0025, 0.005, 0.0075, and 0.01. However, when y exceeds 0.01, the maximum strain (S _max ) decreases gradually. That is, the non-polar phase occupies more than the ferroelectric phase due to too much substitution of KN in the (1-x) BNT-xST phase of ferroelectric phase (for example, x = 0.23) If y is larger than 0.0125, distortion of the lattice becomes more intense due to the substitution of KN, and the strain induced by the electric field is reduced by shifting to the superficial phase.

The composite bismuth lead-free piezoelectric ceramics according to the present invention may have a composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ wherein y is 0.0075 ≤ y ≤ 0.0125. y = 0.0075 and y = 0.0125 show the maximum strain (S _max ) and the normalized strain (d ₃₃ ^* = S _Max / E _Max ) relatively lower than y = 0.01, high maximum strain (S _max) and normalized strain _{(S max / E max) 3} ㎸ / or more in 0.15% low field high maximum strain of ㎜ (S _max) and normalized strain (S _max / E _max) as well as indicate in The range of y may be set to 0.0075 to 0.0125.

In general, a piezoelectric material having a large strain is important for a piezoelectric actuator. Especially, an S _max / E _max (normalized strain, d ₃₃ ^* ) is used as an index to identify a giant strain that is most important in an actuator characteristic. The S _max / E _Max value of 500 pm / V or more is generally required. When the range of y is in the range of 0.0075 to 0.0125, the S _max / E _max value is preferably 500 pm / V at a low electric field of 4 kV / Especially, S _max / E _max value of 600 ㎸ / V or more is very high at 4 ㎸ / ㎜ electric field, so it is very useful when it is applied as an actuator module used in industry, .

4 is a graph _{showing the} relationship between the composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -yKNbO ₃ (y = 0.01) according to an embodiment of the present invention, Fig. 4 (a) is a hysteresis curve showing a unipolar electric field organic strain at an electric field of 3 kV / mm, and Fig. 4 (b) is a hysteresis curve graph showing a unipolar electric field organic strain at an electric field of 4 kV / And FIG. 4 (c) is a hysteresis curve graph showing a unipolar electric field organic strain at an electric field of 5 kV / mm.

Table 4 shows the maximum strain (S _Max ) for each electric field with respect to the composition of (1-xy) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ -y KNbO ₃ (y = 0.01) according to an embodiment of the present invention and Normalization strain (S _Max / E _Max ).

y = 0.01 S _Max S _Max / E _Max 3 kV / mm 0.23 766 4 kV / mm 0.31 775 5 kV / mm 0.34 680

4 and Table 4, the composite bismuth lead-free piezoelectric ceramics according to the present invention can have a maximum strain (S _Max ) of 0.15 to 0.35% in an electric field of 3 to 4 kV / mm. Table 2 shows that the maximum strain (S _Max ) was 0.15% or more when y was 0.0075 ≤ y ≤ 0.0125 in an electric field of 3 kV / mm. Table 3 shows that y (S _max ) of 0.15% or more when 0.0075 ≤ y ≤ 0.0125, and it can be seen from FIG. 4 and Table 4 that as the electric field increases from 3 ㎸ / ㎜ to 4 ㎸ / ㎜ and 5 ㎸ / ㎜ It can be seen that the maximum strain (S _Max ) increases. Therefore, it can be seen that the composite bismuth lead-free piezoelectric ceramics according to the present invention has a maximum strain (S _Max ) of 0.15 to 0.35% in an electric field of 3 to 4 kV / have.

Conventional bismuth piezoelectric ceramics are difficult to apply to actuator modules applied in the industry due to a maximum strain (S _max ) lower than 0.1% at a low electric field of 3 kV / mm. However, in the composite bismuth-based lead-free piezoelectric ceramics Has a maximum strain (S _Max ) of 0.15% or more even in a low electric field of 3 kV / mm, so that it can be applied without difficulty to an actuator module used in the whole industry.

The composite bismuth lead-free piezoelectric ceramics according to the present invention may have a normalization strain (S _Max / E _Max ) of 500 to 800 pm / V at an electric field of 3 to 4 kV / mm. As can be seen from Tables 2 to 4, when the range of y is 0.0075 to 0.0125, it can be confirmed that the normalized strain (S _Max / E _Max ) is more than 500 pm / V at 3 to 4 kV / mm. It can be confirmed that the normalized strain (S _Max / E _Max ) of 700 pm / V or higher at a low electric field of 3 to 4 kV / mm when y is 0.01.

As shown in Table 4, the maximum strain (S _Max ) decreases as the electric field decreases, and the maximum strain (S _Max ) is the lowest at an electric field of 3 kV / mm. However, at a low electric field of 3 to 4 kV / (S _Max / E _Max ) value is higher than that of the high electric field of ㎜ or more. This is because the decrease rate of the maximum strain (S _Max ) is smaller than the decrease rate of the electric field.

Accordingly, the composite bismuth lead-free piezoelectric ceramics according to the present invention may have a normalization strain (S _Max / E _Max ) of 500 to 800 pm / V in an electric field of 3 to 4 kV / mm. In the actuator, a S _max / E _max value of 500 pm / V or more is generally required. The composite bismuth lead-free piezoelectric ceramics of the present invention satisfies this requirement and is very useful when applied to an industrial actuator module In addition, smart actuators with superior performance can be manufactured.

On the other hand, in order to apply it to a smart actuator, it is required to have a high maximum strain (S _Max ) and a normalization strain (S _Max / E _Max ) at a low electric field of 4 kV / / Mm, the complex bismuth lead-free piezoelectric ceramics of the present invention can solve this problem.

In the field of 1 ~ 2 ㎸ / ㎜, the electric field is insufficient and the maximum strain (S _Max ) and the normalization strain (S _Max / E _Max ) sufficient for the smart actuator can not be obtained.

The actuator according to another embodiment of the present invention is a composite bismuth lead-free piezoelectric ceramics according to an embodiment of the present invention; And an electrode for providing an electrical signal to the composite bismuth-based lead-free piezoelectric ceramics.

The composite bismuth-based lead-free piezoelectric ceramics according to one embodiment of the present invention is a composite bismuth lead-free piezoelectric ceramics according to an embodiment of the present invention, which will be described in an embodiment of the present invention, and a detailed description thereof will be omitted.

The material of the electrode is not particularly limited, and a material generally used for a piezoelectric element is sufficient. Examples of the electrode material may include metals of Ti, Pt, Ta, Ir, Sr, In, Sn, Au, Al, Fe, Cr and Ni and oxides of these metals, May be stacked.

The actuator may be a smart actuator, and may be mounted on a micro-electro-mechanical system (MEMS), a camera, a microscope, or the like. Further, excellent performance can be obtained by using the composite bismuth lead-free piezoelectric ceramics of the present invention exhibiting a high strain rate under low-field driving conditions.

In the composite bismuth lead-free piezoelectric ceramics, a ferroelectric phase and a non-polar phase coexist, and when an electric field is applied through the electrode, a phase transition from a nonpolar phase to a ferroelectric phase may occur. The characteristic of the non-polar phase is that when an electric field is applied, a phase transition occurs to a ferroelectric phase, and when the electric field is removed, a phase transition occurs again to a nonpolar phase. The composite bismuth- If a nonpolar phase coexists and an electric field is applied to the composite bismuth-based lead-free piezoelectric ceramics through the electrode, a phase transition occurs in a ferroelectric phase, and if the electric field is removed, a phase transition may occur again in a nonpolar state.

5 is a flowchart illustrating a method of manufacturing a composite bismuth-based lead-free piezoelectric ceramics according to another embodiment of the present invention.

Referring to FIG. 5, a method of manufacturing a composite bismuth-based lead-free piezoelectric ceramic according to still another embodiment of the present invention will be described in detail, and duplicated elements related to the composite bismuth-based leadless piezoelectric ceramic will be omitted.

Another embodiment compound of bismuth-based lead-free piezoelectric ceramic manufacturing method according to the present invention _{(Bi, Na) TiO 3 -SrTiO} 3 forming composition Bi, Na, Sr, an oxide of Ti powder and the (Bi, Na) TiO ₃ is Mixing the oxide powder of K, Nb constituting the substituted KNbO ₃ (S100); Calcining the mixed powder (S200); Forming a formed body by pressing the calcined powder (S300); And sintering the formed body to form a sintered body having a perovskite crystal structure (S400).

First, an oxide powder of Bi, Na, Sr, Ti constituting the (Bi, Na) TiO ₃ -SrTiO ₃ composition is mixed with an oxide powder of K, Nb constituting KNbO ₃ in which (Bi, Na) TiO ₃ is substituted S100). KNbO ₃ (hereinafter referred to as KN) in which the ferroelectric substance (Bi, Na) TiO ₃ (hereinafter referred to as BNT) is substituted has a pseudo-cubic structure of Perovskite type, , Causing a local lattice distortion, leading to a non-polar phase. By replacing KN with some BNT sites, it is possible to derive the proper ratio of ferroelectric phase and nonpolar phase, and obtain the field organic strain value saturating at low electric field.

Next, in order to grow particles of mixed powders, the mixed powder is put into a high-temperature sintering furnace and calcined (S200). At this time, the calcination can be performed at a temperature of 750 to 850 캜 for 1 hour to 3 hours, and the acceleration / deceleration rate can be 3 to 7 캜 / min. If the calcination is carried out at a temperature of 750 ° C or lower, the reaction between the raw powders becomes insufficient. If the calcination proceeds at a temperature higher than 850 ° C, difficulty of pulverization may occur. In addition, if the rate of increase and decrease is too fast, the temperature distribution of the raw material powders becomes uneven, and if it is too slow, the process time becomes long. On the other hand, in order to increase the homogeneity of the mixed powder, it is possible to perform calcination again at a temperature higher than the calcined temperature after repeating the milling and drying. The calcined powder may then be ball milled and pulverized with a dispersion solvent. On the other hand, they may be calcined each time there is added composition.

Then, the calcined powder is placed in a cylindrical mold having a diameter of 10 Ø and molded at a pressure of 1 ton / cm 2 to form a compact (S300). At this time, a small amount (for example, 1 wt%) of a binder (for example, PVA (Polyvinyl Alcohol)) may be added to the calcined powder to facilitate the formation of the powder. The heat treatment may then be carried out in a high-temperature sintering furnace at 600 to 700 ° C for 2 to 4 hours to evaporate the binder and some moisture (for example, adsorbed water [H ₂ O] and adhesion water [OH]) . Here, the rate of acceleration / deceleration can be 3 to 7 占 폚 / min and can be increased or decreased for about 2 hours.

Then, the compact is placed in a high-temperature sintering furnace and sintered to form a sintered body (S400). The sintered body may have a perovskite crystal structure and may be sintered at a temperature of 1,100 to 1,200 ° C for 1 hour to 3 hours. In the sintering, the sintering is not sufficient at a temperature of 1,100 ° C or lower, and the perovskite crystallinity is insufficient. At a temperature of 1,200 ° C or higher, the particle size becomes too large and defects in the structure may occur due to the volatilization of bismuth have. The composite bismuth lead-free piezoelectric ceramics of the present invention is advantageous in that it can be sintered at a relatively lower temperature than conventional PZT piezoelectric materials. Here, the rate of acceleration / deceleration can be 3 to 7 占 폚 / min and can be increased or decreased for about 2 hours.

Next, after the sintered body is polished and cleaned, electrodes are printed on both sides with silver paste, dried in a drying oven at 100 ° C, and then heat-treated at 700 ° C for 10 minutes to form an electrode . The material of the electrode is not limited to this, and a material generally used for a piezoelectric element is sufficient. Examples of the electrode material may include metals of Ti, Pt, Ta, Ir, Sr, In, Sn, Au, Al, Fe, Cr and Ni and oxides of these metals, May be stacked. After the electrode is formed, a piezoelectric element can be manufactured by performing polarization treatment by forming an electric field in the silicone oil. It is preferable that the silicone oil is maintained at a room temperature (25 캜) to 120 캜, and the electric field is preferably 1 to 7 kV / mm.

The sintered body is (1-xy) [(Bi , Na) TiO 3] -xSrTiO 3 -yKNbO 3 may have a composition of (here, wherein x is 0.22 ≤ x ≤ 0.25, said y is 0.0075 ≤ y ≤ 0.0125) . (BNT) and a morphotropic phase boundary (MPB) in the (1-x) [(Bi, Na) TiO ₃ ] -xSrTiO ₃ composition and partially substituted with KN It is possible to induce distortion of the lattice locally to induce the nonpolar image. In this way, it is possible to derive an appropriate ratio of the ferroelectric phase and the nonpolar phase through the substitution of KN, and the field organic strain value saturating in a low electric field can be obtained. Therefore, (1-xy) [( Bi, Na) TiO 3] -xSrTiO 3 -yKNbO 3 ( wherein, wherein x is 0.22 ≤ x ≤ 0.25, said y is 0.0075 ≤ y ≤ 0.0125) is the sintered body having a composition of (S _max ) of not less than 0.15% and a normalized strain (S _Max / E _Max ) of not less than 500 pm / V even in a low electric field of 4 kV / mm or less.

The ferroelectric phase and the nonpolar phase may coexist in the sintered body. The high positive field organic strain occurs when the ferroelectric phase and the nonpolar phase coexist. In the ferroelectric phase (1-x) BNT-xST, the BNT site is partially replaced with a perovskite structure and a pseudo cubic KN The localized lattice distortion occurs due to the substituted KN, and the non-polar phase is induced. Therefore, the position of the BNT having the perovskite crystal structure of ABO _{3 in} the ferroelectric phase (1-x) BNT-xST (for example, x = 0.23) is partially replaced with the perovskite structure and the pseudocubic KN , It is possible to locally induce distortion of the lattice to induce the non-polar image, whereby the ferroelectric phase and the non-polar phase can coexist.

The method for producing a composite bismuth lead-free piezoelectric ceramics of the present invention is a simple production method of a solid-phase reaction method, and its production cost is low and mass production is easy.

Thus, the present invention is a doctor neungmyeon political structure of the (Bi, Na) TiO ₃ based matrix is a cubic structure of SrTiO ₃ was added to the (Bi, Na) TiO ₃ -SrTiO to ₃ solid solution system (Bi, Na) TiO ₃ By partially substituting KNbO ₃ having a cubic crystal structure, it is possible to locally cause distortion of the lattice to induce a nonpolar state. Due to the phase transition behavior depending on the electric field of the non-polar phase, the composite bismuth-based lead-free piezoelectric ceramics of the present invention can have a high electric field organic strain at a low electric field and a low electric field value. The large phase change in the low electric field can be achieved by the phase transition according to the electric field of the nonpolar phase. Therefore, the S _max / E _max (500 kV / V) d ₃₃ ^* ) value. Therefore, when the piezoelectric actuator module is applied, a high electric characteristic can be expected as compared with a low applied voltage. Further, unlike the conventional Pb (Zr, Ti) O ₃ (hereinafter referred to as PZT) which is harmful to the human body and causes environmental pollution, the present invention provides a piezoelectric ceramics material of Bi- Lead-free piezoelectric ceramics can be obtained. The composite bismuth-based piezoelectric ceramics manufacturing method according to the present invention can be manufactured by a simple manufacturing method of a solid-phase reaction method, so that the production cost is low and mass production is easy, and a bismuth (Bi) Friendly.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be construed as limited to the embodiments set forth herein. Those skilled in the art will appreciate that various modifications and equivalent embodiments may be possible. Accordingly, the technical scope of the present invention should be defined by the following claims.

S100: mixed oxide powder S200: calcined
S300: Formation of formed body S400: Formation of sintered body

Claims (12)

(Bi, Na) TiO ₃ based on which the matrix SrTiO ₃ was added (Bi, Na) TiO ₃ -SrTiO ₃ based on the solid solution (Bi, Na) TiO ₃ has a portion of KNbO pseudo cubic crystal (pseudo-cubic) structure ₃ ,
It has a perovskite crystal structure,
(1-xy) [(Bi , Na) TiO 3] -xSrTiO 3 -yKNbO 3 ( wherein x is 0.22 ≤ x ≤ 0.25, said y is 0.0075 ≤ y ≤ 0.0125) having a composition of,
Forming a morphotropic phase boundary (MPB) with a surface roughness and a pseudo cubic phase,
And a normalized strain (S _Max / E _Max ) of 500 to 800 pm / V in an electric field of 3 to 4 kV / mm.
delete delete The method according to claim 1,
The composite bismuth lead-free piezoelectric ceramics have a maximum strain of 0.15 to 0.35% at an electric field of 3 to 4 kV / mm.
delete The method according to claim 1,
Wherein the composite bismuth lead-free piezoelectric ceramics has an absolute value of negative maximum strain of 0 to 0.05% at an electric field of 3 to 4 kV / mm.
The method according to claim 1,
The composite bismuth lead-free piezoelectric ceramics is a composite bismuth lead-free piezoelectric ceramics in which a ferroelectric phase and a nonpolar phase coexist.
The composite bismuth lead-free piezoelectric ceramics of any one of claims 1, 4, and 6 to 7; And
And an electrode for providing an electrical signal to the composite bismuth-based lead-free piezoelectric ceramics.
The method of claim 8,
In the composite bismuth lead-free piezoelectric ceramics, a ferroelectric phase and a nonpolar phase coexist, and a phase transition occurs from a nonpolar phase to a ferroelectric phase when an electric field is applied through the electrode.
(Bi, Na) TiO ₃ -SrTiO _{3 with} an oxide powder of K, Nb constituting KNbO ₃ in which (Bi, Na) TiO ₃ is substituted;
Calcining the mixed powder;
Pressing the calcined powder to form a formed body; And
And sintering the formed body to form a sintered body having a perovskite crystal structure,
The sintered body may be,
Having a composition of (1-xy) [(Bi , Na) TiO 3] -xSrTiO 3 -yKNbO 3 ( where the x is 0.22 ≤ x ≤ 0.25, it said y is 0.0075 ≤ y ≤ 0.0125),
A morphotropic Phase Boundary (MPB) with a surface roughness and a pseudo cubic phase is formed,
And a normalized strain (S _Max / E _Max ) of 500 to 800 pm / V in an electric field of 3 to 4 kV / mm.
delete The method of claim 10,
Wherein the sintered body has a ferroelectric phase and a nonpolar phase coexist.

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