KR101261445B1 - Bismuth-based Lead-free Piezoelectric Ceramics and Manufacturing Method therefor - Google Patents

Abstract

The present invention relates to bismuth (Bi) lead-free piezoelectric ceramics having improved dielectric loss characteristics and a method of manufacturing the same. Bismuth (Bi) based lead-free piezoelectric ceramic according to the present invention has a perovskite (perovskite) crystal structure, as a main component containing Bi, Na, Ti, O (Bi _{0 .5 0 .5} Na) TiO ₃ Is parented and contains NaF as an additive.

Description

Bismuth-based lead-free piezoelectric ceramics and a method of manufacturing the same {Bismuth-based Lead-free Piezoelectric Ceramics and Manufacturing Method therefor}

The present invention includes a bismuth for a bismuth (Bi) based lead-free piezoelectric ceramic, and relates to a method of manufacturing the same, and more particularly, (Bi _{0 .5 0 .5} Na) as NaF, and a TiO ₃ additive in the matrix (Bi) It relates to a system of lead-free piezoelectric ceramics and a method of manufacturing the same.

In general, piezoelectric ceramics are used in filters, piezoelectric transformers, and the like in medical devices, sensor devices, home electronics, and precision measurement devices because of their excellent piezoelectric and dielectric properties.

Piezoelectric ceramics, which are mainly used at present, are generally manufactured using PZT-based powders having a Pb (Zr, Ti) O ₃ (hereinafter referred to as “PZT”)-based composition. , ZrO ₂ and TiO ₂ are mixed using a solid phase synthesis method obtained by mixing raw materials such as MgO and Nb ₂ O ₅ , which are impurities, and baking at high temperature.

However, since the piezoelectric properties of the PZT-based powders vary greatly depending on their composition, very precise control is required for the capacity control of MgO, Nb ₂ O _5, etc., added as impurities.

The PZT-based powder should be sintered at a relatively high temperature between 1200 ° C and 1350 ° C. In the sintering process, a large amount of PbO is volatilized, making it difficult to control the microstructure and physical properties. It causes the cause. In addition, when manufacturing a multilayer piezoelectric element using PZT piezoelectric ceramics, there is a problem that a high melting point metal such as platinum (Pt) or lead (Pd) must be used as an internal electrode due to a high sintering temperature. When manufacturing piezoceramic / metal composites using ceramics, piezoelectric ceramics / metal composites are first sintered after piezoceramic / metal composites are sintered to prevent metals from being oxidized. There exists a problem that interface characteristics, such as these, fall.

In order to solve this problem it had been proposed a variety of non-associated piezoelectric ceramic, in which Bi-based lead-free piezoelectric ceramic materials as _{(Bi 0 .5 Na 0 .5)} TiO 3 (BNT) , and (Bi _{0 .5 0 .5} K TiO ₃ (BKT). Compositionally expressed as ABO ₃ , in the case of BNT, Bi ^{3 +} and Na ^{1 +} coexist at A site, and in the case of BKT, Bi ^{3 +} and K ^{1 +} coexist at the perovskite complex ( provskite) structure. BNT is a ferroelectric piezoelectric element having a rhombohedral structure at room temperature, and BKT is a ferroelectric piezoelectric element having a positive discharge structure at room temperature.

On the other hand, the stoichiometric composition in the ABO ₃ perovskite structure is Bi ^{3 +} = 0.5 at A site, Na ^{1 +} = 0.5 or K ^{1 +} = 0.5, and Ti at B site as described above. ^{4 +} = 1.0, the number of cation valence electrons is + 6 to maintain electrical neutrality with -6 of the three oxygen ions. In the case of deviation from the stoichiometric composition due to cation deficiency, charge compensation occurs within a certain range. In order to maintain electrical neutrality, cations or anions are formed, and oxygen vacancies, which are anions, are frequently generated. These oxygen vacancies have fluidity in the piezoelectric body in a charged state, and cause difficulty in reproducibility by causing changes in piezoelectric or dielectric properties of the piezoelectric body, such as forming an internal bias field by forming dipoles with other defects. In particular, when an alternating current is applied to a dielectric, it is pointed out as a problem that reduces the dielectric loss characteristic, which is an energy loss lost by heat in the dielectric, thereby preventing the practical use of Bi-based lead-free piezoelectric ceramics.

The present invention is to solve the above-mentioned problems, the main component is (Bi _0.5 Na _0.5 ) TiO ₃ containing Bi, Na, Ti, O as a parent, and added NaF as an additive to perovskite Bismuth (Bi) lead-free piezoelectric ceramics having improved dielectric and piezoelectric properties including dielectric loss characteristics by controlling oxygen vacancies easily expressed in (perovskite) crystal structure piezoelectric ceramics and a method of manufacturing the same.

Bismuth (Bi) based lead-free piezoelectric ceramic according to an embodiment to the present invention has a Fe lobe Sky agent (perovskite) crystal structure, as a main component containing Bi, Na, Ti, O (Bi _{0 .5 0 .5} Na ) TiO ₃ as a parent and contains NaF as an additive.

At this time, the bismuth (Bi) -based lead-free piezoelectric ceramics satisfy the following formula (1).

A _x F _x, wherein x is 0.001 <x <0.01 _- <Formula _{1> (Bi 0 .5 Na 0} .5) TiO 3.

The bismuth (Bi) -based lead-free piezoelectric ceramics have a dielectric loss (tanδ) measured at 100 kHz of more than 0% and less than 10%.

The bismuth (Bi) -based lead-free piezoelectric ceramics form a solid solution.

Bismuth (Bi) -based lead-free piezoelectric ceramics manufacturing method according to another embodiment of the present invention is mixed with Bi ₂ O ₃ , Na ₂ CO ₃ , TiO ₂ powder constituting the mother and NaF powder additives, followed by calcination and grinding Forming an intermediate compound powder; Pressing the intermediate compound powder to form a shaped body; And sintering the formed body to form a sintered body having a perovskite crystal structure.

The bismuth (Bi) -based lead-free piezoelectric ceramics satisfy the following formula (1).

A _x F _x, wherein x is 0.001 <x <0.01 _- <Formula _{1> (Bi 0 .5 Na 0} .5) TiO 3.

The bismuth (Bi) -based lead-free piezoelectric ceramics have a dielectric loss (tanδ) measured at 100 kHz of more than 0% and less than 10%.

The bismuth (Bi) -based lead-free piezoelectric ceramics form a solid solution.

The calcination is carried out for 1 hour to 2 hours at a temperature of 900 ℃ to 1000 ℃, the sintering is carried out for 1 hour to 2 hours at a temperature of 1100 ℃ to 1200 ℃.

According to the bismuth (Bi) -based lead-free piezoelectric ceramics and the manufacturing method thereof according to the present invention, it is possible to improve the stability and reproducibility of the piezoelectric ceramics containing no lead (Pb), which is subject to environmental regulation, and to prevent environmental pollution. Can be. In addition, it is possible to manufacture a piezoelectric element having excellent dielectric and piezoelectric characteristics including dielectric loss characteristics, improved reliability, and environment-friendly.

1 is a flow chart showing a method for producing bismuth (Bi) -based lead-free piezoelectric ceramics according to the present invention.
Figure 2 is (Bi _{0 .5 0 .5} Na) TiO ₃ in accordance with the present _invention a graph showing the X-ray diffraction properties of the composition of _x F _x.
Figure 3 (Bi _{0 .5 0 .5} Na) TiO ₃ in accordance with the present _invention a graph showing the dielectric loss (tanδ) in accordance with the temperature and frequency of the _x F _x.

The following detailed description of specific embodiments provides several descriptions of specific embodiments of the present invention. However, the present invention can be implemented in many different ways, which are defined and covered by the claims. The detailed description is described with reference to the drawings, wherein like reference numerals refer to the same or functionally similar elements.

Hereinafter, a bismuth (Bi) -based lead-free piezoelectric ceramic according to a preferred embodiment of the present invention and a manufacturing method thereof will be described with reference to the accompanying drawings.

1 is a flowchart illustrating a method of manufacturing bismuth (Bi) -based lead-free piezoelectric ceramics according to the present invention.

First, perovskite (perovskite) constituent elements for the production of bismuth (Bi) based lead-free piezoelectric ceramic having a crystal structure of the ABO ₃ Bi, Na, Ti, the matrix containing the O (Bi _{0 .5} Na _{0. 5} ) Bi ₂ O ₃ , Na ₂ CO ₃ , TiO ₂ powder constituting TiO ₃ and NaF powder as an additive are weighed according to the molar ratio and mixed (S100). In this case, the bismuth (Bi) based lead-free piezoelectric ceramics (Bi _{0 .5 0 .5} Na) TiO _{3 - x} to satisfy the composition formula of F _x, the variable x to determine the composition herein was selected from 0 ≤ x ≤ 0.03. Powders weighed according to molar ratio were mixed by ball milling with ethyl alcohol or methyl alcohol as dispersion solvent. The ratio of the dispersion solvent and the ball is 1: 1, and the used ball is wet mixed with zirconia ball for 24 hours.

Next, the mixed powder is placed in an alumina crucible, calcined by heat treatment at a temperature of 800 ° C. to 1000 ° C. for 1 to 3 hours, and then crushed by ball milling using a dispersion solvent and zirconia balls again. To form an intermediate compound powder (S200). At this time, TG (differential thermal analysis) was measured for the powder mixed with each starting material, and the preferred calcining temperature was determined in parallel with the XRD analysis for the calcined powder. Decided. The calcination was carried out for 1 hour to 3 hours at a temperature of 800 ℃ to 1000 ℃, the reaction between the raw powders at a temperature below that was not enough, there is a disadvantage that the subsequent procedure is difficult to grind above the temperature.

After calcination, a small amount of binder was added to the pulverized intermediate compound powder to homogenize the particle diameter to 10 μm or less, and then a molding pressure of 1 ton / cm 2 was applied to form a compact by pressing into a disk-shaped specimen having a diameter of 10 mm (S300). At this time, the binder is preferably added 5wt% 10% PVA aqueous solution as a binder.

The compact was heated at a rate of 1 ° C./min for 2 hours, and maintained at 250 ° C. for 2 hours to evaporate adsorbed water (H ₂ O) and adhered water (OH), and bound water contained in the crystal at 600 ° C. Binders such as (OH) and a binder were volatilized. Thereafter, by using a platinum plate heat treatment at a temperature of 1050 ℃ to 1250 ℃ for 1 hour to 3 hours to form a sintered body having a perovskite crystal structure (S400). If the sintering temperature is 1050 ° C. or lower, the sintering is not sufficient, so the perovskite crystallinity is not sufficient. If the sintering temperature is higher than 1250 ° C., the particle size is too large and defects in the structure may occur due to volatilization of bismuth. At this time, in order to prevent volatilization of bismuth, the calcined BNT powder may be put into the atmosphere powder in the crucible. Bismuth (Bi) -based lead-free piezoelectric ceramic of the present invention has the advantage that can be sintered at a relatively lower temperature than the conventional PZT.

After polishing and washing the sintered body, a silver paste was screen printed on both sides, dried in a 100 ° C. dry oven, and then baked at 600 ° C. for 10 minutes to form an electrode. Subsequently, a piezoelectric element is manufactured by applying a voltage from silicon oil in order to polarize (S500). It is preferable that the temperature of the said silicone oil is the temperature of normal temperature-120 degreeC, and it is preferable that a voltage applies 1-5KV / mm.

The manufacturing process of the piezoelectric ceramic or piezoelectric element according to the present invention is not limited to the above, and various modifications and changes are possible depending on the characteristics of the desired element and the convenience of the process.

Thus, according to the present invention, by synthesizing into a solid solution containing (Bi _0.5 Na _0.5 ) TiO ₃ matrix containing Bi, Na, Ti, O as the main component and NaF additive, it does not contain Pb and perovskite (perovskite Bismuth (Bi) -based lead-free piezoelectric ceramics having a crystal structure can be prepared. Accordingly, in the case of the conventional PZT ceramics, the piezoelectric ceramics of the present invention can obtain sintered water stable characteristics, in particular, an environmentally friendly advantage, while the dispersion of properties is large and it is difficult to secure reproducibility due to volatilization of PbO during sintering.

In addition, according to the present invention, the piezoelectric ceramics manufactured as described above may have excellent electrical characteristics, improved reliability, and environmentally friendly piezoelectric elements.

Figure 2 is (Bi _{0 .5 0 .5} Na) TiO ₃ in accordance with the invention _{- x} F _x X-ray diffraction in accordance with the composition of: a graph showing the (X-ray Diffraction XRD) characteristics. This is to determine the crystal structure by injecting a specific X-ray beam while varying the angle on the surface of the piezoelectric ceramic to be analyzed and reading the intensity of the diffracted X-ray beam according to the characteristics of the crystal plane. Perovskite As shown in Figure 2 is only observed major XRD peaks (peak) is found in the tree structure determination (Bi _{0 .5 0 .5} Na) TiO ₃ It was confirmed that the secondary phase did not occur in all the specimens to which NaF was added in the base material and various molar ratios, and the single phase perovskite compound was well synthesized in the solid solution state. These compounds remain stable until their melting point.

After calculating the theoretical density using the lattice constant obtained through XRD analysis of the sintered specimens, the relative density was determined by comparing with the sintered density obtained by the Archimedes method. _{(Bi 0 .5 Na 0 .5)} TiO 3 - x F _x is the relative density showed over 95% for all NaF addition amount, the relative density did not show the tendency that change in accordance with the particular NaF was added.

Table 1 (Bi _{0 .5 0 .5} Na) TiO ₃ prepared according to the present invention and a bismuth-based (Bi) of the lead-free piezoelectric ceramic composition of (Bi _{0 .5 0 .5} Na) TiO _{x 3- x} F of the following composition Bismuth (Bi) is a comparison of the characteristics of lead-free piezoelectric ceramics, and shows measured values of dielectric constant, electromechanical coupling coefficient (Kt) and dielectric loss (tanδ) in the thickness direction. All comparative bismuth-based (Bi) lead-free piezoelectric ceramics were sintered at 1100 ° C. for 2 hours.

permittivity Kt (%) tanδ (%) (Bi _0.5 Na _0.5 ) TiO ₃ 306.3 30.5 16.0 (Bi _0.5 Na _0.5 ) TiO _2.999 F _0.001 309.7 31.6 3.0 (Bi _0.5 Na _0.5 ) TiO _2.997 F _0.003 307.6 32.1 3.0 (Bi _0.5 Na _0.5 ) TiO _2.995 F _0.005 309.5 33.7 4.9 (Bi _0.5 Na _0.5 ) TiO _2.99 F _0.01 310.6 32.3 5.0 _{(Bi 0 .5 Na 0 .5)} TiO 2 .97 F 0.03 307.1 31.2 11.0

If the dielectric constant and the electromechanical coupling factor (Kt) in the thickness direction as shown in the Table 1 which does not include the participation NaF water _{(Bi 0 .5 Na 0 .5)} (Bi 0 containing TiO ₃ and NaF _{additives. 5 Na 0 .5) TiO 3 -} x F x on the other hand, larger values indicating a similar characteristic difference between no audio, the NaF does not include participation water in the case of the dielectric loss (tanδ) measured at a measurement frequency of 100kHz and at room temperature ( Bi _0.5 Na _0.5 ) TiO ₃ represents a dielectric loss value of 16%, and the composition range of (Bi _0.5 Na _0.5 ) TiO _3-x F _x is in the range of 0.001 ≦ x ≦ 0.01 with the addition of NaF additives from 3.0% to It can be seen that the dielectric loss is lowered to 5.0%. Oxygen vacancy, which is a common defect in oxide piezoelectric ceramics with a perovskite crystal structure, is charged in the piezoelectric body in a charged state, and forms an internal bias field by forming dipoles with other defects. It is known that a problem occurs in terms of reproducibility by generating a change in electrical characteristics, and in particular, causes a problem of lowering dielectric loss characteristics, which are energy losses lost by heat in the piezoelectric body, particularly when an AC electric field is applied to the piezoelectric body. In the present invention, when NaF is added to (Bi _0.5 Na _0.5 ) TiO ₃ , fluorine (F) is substituted into the oxygen site in the perovskite crystal structure to have an effective charge of +1, The fluorine (F) occupying the oxygen site reduces the oxygen vacancy with an effective charge of +2. However, when NaF is added (Bi _0.5 Na _0.5 ) TiO _2.97 F _0.03 , fluorine (F) acts as a defect and adversely affect the dielectric loss characteristics. Therefore, the composition ratio of NaF is preferably selected between 0.001 and 0.01 ((Bi _0.5 Na _0.5 ) TiO _3-x F _x , where x is 0.001 <x <0.01).

Figure 3 is according to the present invention (Bi _{0 .5 0 .5} Na) TiO _{3 -} a graph showing the dielectric loss (tanδ) of the composition of _x F _x, 3 (a) is the (Bi ₀ measured at 10kHz _.5 Na _{0 .5)} TiO ₃ and _{(Bi 0.5 Na 0.5) TiO 2.995} F 0.005 , and a graph showing the dielectric loss along with the value of the piezoelectric ceramic in the temperature, FIG. 3 (b) _{(Bi 0.5 Na 0.5) TiO 2.995} F 0.005 It is a graph showing the dielectric loss value of piezoelectric ceramics according to temperature and measurement frequency. In Figure 3 (a) the entire temperature range of practical use temperatures below the 150 ^o C of the piezoelectric element as shown in (Bi _0.5 Na _0.5) TiO ₃ than _{(Bi 0.5 Na 0.5) TiO 2.995} F 0.005 a low dielectric loss characteristic The value is shown stably. On the other hand, the decrease in the dielectric loss value with the addition of NaF was more pronounced at high frequencies. As shown in FIG. 3 (b), the bismuth-based (Bi) piezoelectric ceramics to which NaF was added exhibited low dielectric loss values of less than 10% even at a measurement frequency of 1 MHz and a high temperature region, while the piezoelectric ceramics to which NaF was not added. Has a dielectric loss of more than tens of percent. Low dielectric loss characteristics in the high frequency region of 1 MHz or more are stable in the composition (x) range of 0.004 to 0.006 (0.004 <x <0.006).

, The main component according to the present invention as described above, Bi, Na, Ti, containing O (Bi _0.5 Na _0.5) by the addition of the NaF TiO ₃ in the matrix (Bi _{0 .5 0 .5} Na) TiO Compared to ₃ , it is possible to obtain bismuth (Bi) lead-free piezoelectric ceramics having excellent dielectric and piezoelectric properties while significantly reducing the dielectric loss value. In addition, since the piezoelectric ceramics of the present invention do not contain Pb, it is possible to prevent the reliability deterioration of characteristics due to volatilization of PbO during sintering, thereby ensuring stability and reproducibility of the synthesized piezoelectric ceramics, and causing Pb to cause environmental problems. There is an environmentally friendly advantage because it does not include.

Although the present invention has been described with reference to one embodiment shown in the drawings, this is merely exemplary, and those skilled in the art will understand that various modifications and equivalent other embodiments are possible therefrom. .

Claims (10)

Has a perovskite crystal structure,
It is based on (Bi _0.5 Na _0.5 ) TiO ₃ containing Bi, Na, Ti, O as its main component, and contains NaF as an additive,
Bismuth (Bi) -based lead-free piezoelectric ceramics, characterized by satisfying the formula (1).
<Formula 1>
(Bi _0.5 Na _0.5 ) TiO _3-x F _x , where x is 0.001 <x <0.01.
delete The bismuth (Bi) lead-free piezoelectric ceramics according to claim 1, wherein the dielectric loss tanδ measured at 100 kHz is greater than 0% and less than or equal to 10%.
The bismuth (Bi) -based lead-free piezoelectric ceramics according to claim 1, wherein a solid solution is formed.
Mixing the Bi ₂ O ₃ , Na ₂ CO ₃ , TiO ₂ powder constituting the mother powder with NaF powder as an additive, and then calcining and grinding to form an intermediate compound powder;
Pressing the intermediate compound powder to form a shaped body; And
Sintering the molded body to form a sintered body having a perovskite crystal structure,
Method for producing a bismuth (Bi) -based lead-free piezoelectric ceramics, characterized by satisfying the formula (1).
<Formula 1>
(Bi _0.5 Na _0.5 ) TiO _3-x F _x , where x is 0.001 <x <0.01.
delete The method of claim 5, wherein the bismuth (Bi) lead-free piezoelectric ceramics have a dielectric loss (tanδ) measured at 100 kHz of more than 0% and 10% or less.
The method for manufacturing bismuth (Bi) lead-free piezoelectric ceramics according to claim 5, wherein the bismuth (Bi) lead-free piezoelectric ceramics form a solid solution.
The bismuth (Bi) lead-free piezoelectric ceramics according to any one of claims 5, 7, or 8, wherein the calcination is performed at a temperature of 800 ° C to 1000 ° C for 1 hour to 3 hours. Method of preparation.
9. The bismuth (Bi) lead-free piezoelectric ceramics according to claim 5, 7 or 8, wherein the sintering is performed at a temperature of 1050 ° C. to 1250 ° C. for 1 hour to 3 hours. Manufacturing method.

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