KR100966595B1 - Perovskite Lead-free piezoelectric ceramics and preparation method - Google Patents

Abstract

The present invention has a perovskite (Perovskite) crystal _{structure, {Li x (K 0 .5} Na 0 .5) 1-x} NbO 3 Weighing and preparing a raw material powder to obtain a lead-free piezoelectric ceramic having a composition of (0.01 ≦ x <0.03); Mixing the primary powder, pulverizing and calcining to prepare a primary powder; On the primary powder Preparing a secondary powder by adding 0.2 to 1.0 wt% of at least one of Fe ₂ O ₃ , Bi ₂ O ₃ , V ₂ O ₅ , MnO _2, or ZnO, mixing, and grinding; Preparing a specimen by adding a binder to the secondary powder and molding under pressure; And heating the specimen to volatilize and sinter the binder; Provided is a method of manufacturing a lead-free piezoelectric ceramic.

Lead-free Piezoelectric Ceramics, Oxide Additives

Description

Lead-free piezoelectric ceramics having a perovskite structure and a method of manufacturing the same {Perovskite Lead-free piezoelectric ceramics and preparation method}

The present invention relates to a perovskite-free connection and a method of manufacturing the piezoelectric ceramic has a structure, more specifically, page lobe having a tree structure Sky _{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO _{The present} invention relates to a lead-free piezoelectric ceramics and a method of manufacturing the same, which are obtained by adding oxide additives to the oxide mixture to obtain lead-free piezoelectric ceramics having improved physical properties including temperature stability.

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 will act as a cause.

In addition, when manufacturing a multilayer piezoelectric element using PZT-based 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 piezoelectric ceramics / metal composites using PZT-based piezoelectric ceramics, the piezoelectric ceramics / metal composites are sintered first and then piezoelectric ceramics / metal composites are sintered to prevent the metal from being oxidized. There is a problem in that interfacial properties such as metal bonding strength are lowered.

To solve this problem, lead-free piezoelectric ceramics have been proposed, but a phase transition from the Orthorhombic phase to the tetragonal phase (hereinafter referred to as the T _{o -t} phase transition) occurs in a temperature range that is commonly used, resulting in variations in the resonance frequency and the anti-resonant frequency. Piezoelectric properties and temperature stability, such as the reduction of the electromechanical coupling coefficient and the thermal shock durability is reduced, and thus the problem of poor practicality remains a problem. In particular, when used as an automotive electronic component, it is required to maintain stable characteristics at a high temperature range (-40 ° C. to 150 ° C.) compared to general home appliances, but lead-free piezoelectric ceramics have not shown these characteristics. . Also noted as existing _{(K 0 .5 Na 0 .5)} 1} NbO 3 based ceramics are great problems in a low density by the abnormal grain growth and ovarian formed in the drawback that the leakage current is large, to obtain the desired properties in practical use It was.

In order to solve this problem, methods such as reactive template grain growth (RTGG), hot pressing, hot forging (HF), spark plasma sintering (SPS), etc. Have been tried, these methods are also difficult to fabricate and have poor reproducibility.

The present invention been made to solve the above problems, perovskite (Perovskite) has a crystal structure, a composition formula _{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO 3 as Li, K Elemental elements of Na, Nb, and O are main components, and oxide additives are added thereto and heat-treated to change the phase transition temperature to provide lead-free piezoelectric ceramics having improved temperature stability and piezoelectric properties, and a method of manufacturing the same. will be.

The present invention for achieving the above object has a perovskite (Perovskite) crystal structure, Fe ₂ in a lead-free piezoelectric ceramics composed of the composition of {Li _x (K _0.5 Na _0.5 ) _1-x } NbO ₃ A lead-free piezoelectric ceramic is provided, wherein any one or more of O ₃ , Bi ₂ O ₃ , V ₂ O ₅ , MnO _2, or ZnO is added.

Wherein the _{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO 3 is a non-associated piezoelectric ceramic having a composition range of (0.01≤x <0.03), the _{Fe 2 O 3, Bi 2 O} 3 , V ₂ O ₅ , MnO ₂ Or it is characterized by providing a lead-free piezoelectric ceramics, characterized in that any one or more of ZnO is added 0.2 ~ 1.0wt%.

In addition, another object of the present invention have a perovskite (Perovskite) crystal _{structure, {Li x (K 0 .5} Na 0 .5) 1-x} NbO 3 Weighing and preparing the raw material powder to obtain a lead-free piezoelectric ceramic having a composition of (0.01 ≦ x <0.03); Preparing a primary powder by mixing and pulverizing the raw powder, and then calcining (? 燒, calcine) for 4 to 6 hours at a temperature range of 750 ° C. to 950 ° C .; On the primary powder Preparing a secondary powder by adding 0.2 to 1.0 wt% of Fe ₂ O ₃ , Bi ₂ O ₃ , V ₂ O ₅ , MnO _2, or ZnO, mixing, and grinding; Adding a binder to the secondary powder and forming a specimen by pressure molding; Heating the specimen to volatilize the binder and sintering at 900 ° C. to 1100 ° C .; After polarizing the sintered specimen, it is achieved by providing a method for producing lead-free piezoelectric ceramics, which comprises the step of heat treatment at 100 ° C to 200 ° C.

The present invention provides the following effects by providing a lead-free piezoelectric ceramics and a manufacturing method thereof.

First perovskite has a crystal structure of _{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO 3 Such as Fe ₂ O ₃ , Bi ₂ O ₃ , V ₂ O ₅ , MnO ₂ or ZnO By adding oxide additives, the mechanical properties such as electromechanical coupling coefficient, dielectric constant and piezoelectric constant are excellent. Especially, the piezoelectric properties required within the commercial temperature range of automotive electronic parts (-40 ℃ ~ 150 ℃) can be kept constant. It is possible to manufacture lead-free piezoelectric ceramics having excellent temperature stability.

In addition, compared to conventional PZT-based piezoelectric ceramics, the use of lead-based compounds does not solve the problem of physical property control and environmental problems caused by volatilization of PbO. In other words, it does not use lead or lead compounds, so it can cope with environmental regulations such as Restriction of Hazardous Substances (RoHS) Directive and Waste Electrical and Electronic Equipment (WEEE) Directive.

Finally, it is simpler than conventional reactive template grain growth (RTGG), hot pressing, hot forging (HF), spark plasma sintering (SPS), etc. Since the process is carried out by the oxide mixing method has good reproducibility, there is an advantage that the manufacturing cost is reduced.

First, a method of manufacturing piezoelectric ceramics according to the present invention will be described with reference to specific examples.

_{{Li x (K 0 .5 Na} 0 .5) 1-x} of the perovskite (Perovskite) having the structure of ABO ₃ component element for the production of NbO ₃ based piezoelectric three remix Li, K, Na, Nb And O is weighed according to the molar ratio and mixed to prepare a raw material powder.

And it depends on the composition formula of this time mol (mole) ratios of the elements _{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO 3, the composition range is to be (0.01≤x <0.03). The composition range corresponds to a range in which the temperature stability and piezoelectric properties of the piezoelectric ceramics are greatly improved, and when it is out of the range of (0.01≤x <0.03), the overall piezoelectric properties are deteriorated due to a decrease in sintering properties. The problem arises in temperature stability.

After the dispersion by adding the dispersion solvent to the raw material powder to the first ball milling, and then pulverized (calcinations) for 4 to 6 hours at 750 ℃ ~ 950 ℃ to prepare a primary powder.

Oxide additives to the primary powders were Fe ₂ O ₃ , Bi ₂ O ₃ , V ₂ O ₅ , MnO ₂ Alternatively, at least one of ZnO is added to 0.2 wt% to 1.0 wt%, followed by secondary ball milling, followed by drying and sieving to prepare a secondary powder.

A small amount of binder was added to the prepared secondary powder to uniformize the particle size to 10 μm or less, and then a molding pressure of 1 ton / cm 2 was applied to the secondary powder to prepare a disk type specimen having a diameter of 1 cm. At this time, the binder is preferably PVA (polyvinylalcohol).

The specimen is heated at a rate of 1 ° C./min for 2 hours, and the binder such as adsorbed water and adhering water is evaporated at 250 ° C., and the binder such as binder water and binder is evaporated at 600 ° C. FIG.

Next, sinter the specimen by heat treatment at 900 ℃ ~ 1100 ℃ for 2 hours using a platinum (Pt) plate, and then polish and wash the sintered specimen, and then screen-print silver paste on both sides for 10 minutes at 700 ℃. After preheating, a silver (Ag) electrode is coated and polarized by applying a voltage of 3 to 5 kV / mm for 30 minutes in silicon oil.

Finally, the polarized specimens are heat treated. At this time, it is preferable that the temperature at which the piezoelectric ceramics are heated to be heat-treated at a temperature at which the crystal system is stable or higher is in the range of 100 ° C to 200 ° C. The heat treatment process corresponds to a heat aging process for stabilizing piezoelectric properties.

Figure 1 _{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO 3 (However, when the oxide additive is added to the piezoelectric ceramics corresponding to the composition formula of 0.01≤x <0.03), it is a graph showing the results of X-ray diffraction (XRD) experiment. The experiment involves determining the crystal structure by injecting a specific X-ray beam with varying angles on the surface of the piezoelectric ceramic to be analyzed and reading the intensity of the diffracted X-ray beam depending on the characteristics of the crystal plane.

(a) is a profile when oxide additives are not added to piezoelectric ceramics, (b) is MnO ₂ , (c) is V ₂ O ₅ , (d) is Bi ₂ O ₃ , (e) is a profile of the insert when the oxide additives for the Fe ₂ O _3, respectively. As a result of the analysis, since peak waveforms are observed at the same diffraction angle, it can be confirmed that (a) to (e) all show the same phase structure. As a result, it can be seen that the presence or absence of the oxide additive does not affect the phase structure of the piezoelectric ceramics.

2 is a graph showing the thermal shock test results of the piezoelectric ceramics according to the present invention.

This experiment was to determine the temperature stability of the amount of lithium (Li) piezoelectric ceramic _{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO 3.

_{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO 3 The (a) sample and the lithium (Li) content were adjusted to 3 mol% (x = 0.03) by adjusting the lithium (Li) content of the piezoelectric ceramics composed of the formula to 1 mol% or more and less than 3 mol% (0.01≤x <0.03) ( b) The experiment was divided into samples. The experiment was performed by increasing the temperature of the two samples from 30 ° C. to 150 ° C. and then again decreasing the temperature from 150 ° C. to 30 ° C. and measuring the electromechanical coupling coefficient (Kp).

As shown, the (b) sample having a lithium content of 3 mol% shows a large drop in the electromechanical coefficient when the temperature is lowered from 150 ° C to 30 ° C, but the lithium content is less than that. (a) In the case of sample, the change of electromechanical coefficient was only 8.1% during the temperature change of rising and falling between 30 ℃ and 150 ℃.

As a result, in the case of the (a) sample in which the content of lithium (Li) is 1 mol% or more and less than 3 mol%, since the T _{o -t} phase transition temperature at which the crystal structure is changed by thermal shock becomes 150 ° C. or more, the experiment section (30 ° C.≤T ≦ 150 ° C.), the electromechanical coefficient remains constant.

However, if the amount of lithium (Li) with low sintering property is lowered deteriorate the piezoelectric characteristics, but a problem with this problem oxide additive _{(Fe 2 O 3, Bi 2} O 3, V 2 O 5, MnO 2 Or ZnO). Therefore, the _{{Li x (K 0 .5 Na} 0 .5) 1-x} NbO 3 (0.01≤x <0.03) that corresponds to the one embodiment of the present invention, _{Fe 2 O 3, Bi 2 O} 3, V 2 O ₅ , such as MnO ₂ or ZnO Piezoelectric ceramics added with oxide additives maintain both temperature stability and piezoelectric properties.

3 is a graph showing the temperature change of the T _{o -t} phase transition of piezoelectric ceramics by an oxide additive.

This experiment is based on Fe ₂ O ₃ ,, MnO _{2 ,} V ₂ O ₅ Alternatively, ZnO was added to the piezoelectric ceramics to measure the dielectric constants with temperature.

As shown, Fe ₂ O ₃ , MnO ₂ , V ₂ O ₅ , which is a kind of oxide additive Or when ZnO is added, it can be seen that the temperature of the phase transition from the Orthorhombic phase to the tetragonal phase is higher than 150 ° C. From this, it can be seen that the lead-free piezoelectric ceramics prepared according to the present invention are excellent in temperature stability in which T _{o -t} phase transition does not occur in the temperature range (-40 ° C. to 150 ° C.) that we usually use.

4 is a perspective view and a cross-sectional view showing an example of a piezoelectric ceramic vibrator according to the present invention.

The piezoelectric ceramic vibrator shown is made of the piezoelectric composition according to the present invention described above, and lead-free silver electrodes are coated on the upper and lower portions thereof, and are polarized in the thickness direction as indicated by the arrows.

Table 1 below shows the piezoelectric properties of the piezoelectric ceramic elements according to the oxide additives based on the planar vibration mode of the disk-shaped vibrator made of piezoelectric ceramics. The piezoelectric characteristics adopt optimal values while controlling process conditions such as firing temperature, polarization temperature, and polarization voltage.

TABLE 1

Piezoelectric properties
( piezoelectric properties ) Without additives Fe ₂ O ₃ Bi ₂ O ₃ V ₂ O ₅ MnO ₂ ZnO Electromechanical Coupling Factor
( Electromechanical coupling factor , Kp (%)) 26 27 42 21 31 39 Piezoelectric charge coefficient
( piezoelectric charge sensor constant , d ₃₃ ( pC / N)) 141 91 139 125 109 127 Piezoelectric Voltage Factor
( piezoelectric voltage constant , g ₃₃ ) 20.61 23 35 25 37 43 Dielectric constant ( dielectric constant ) 315 447 440 555 335 335 Mechanical quality factor
( mechanical quality factor , Qm ) 59.25 96 103 73 123 200

First, the piezoelectric coupling factor (Kp (%)) is a coefficient representing the rate of change between electrical energy and mechanical energy. It is a criterion for evaluating the piezoelectric properties of a material. It is large. As can be seen from the table, when the oxide additive is added, it can be seen that the electromechanical coupling coefficient is generally larger than that when it is not added.

Next, the experimental results of the piezoelectric charge coefficient and the piezoelectric voltage coefficient, which are a kind of electromechanical piezoelectric constant, are a parameter representing the relationship between the electrical signal and the mechanical response. The piezoelectric charge sensor constant (d ₃₃ (pC / N)) is a measure of the amount of charge that occurs when a constant stress is applied, or a measure of the strain that occurs when a constant electric field is applied. see.

The piezoelectric voltage constant (g ₃₃ ) is a measure of how much an electric field is generated when stress is applied to the piezoelectric body. In general, when the value of the piezoelectric voltage coefficient is large, high voltage occurs at the same stress, so the piezoelectric property is good. As can be seen from the table, when the oxide additive is added, it can be seen that the value of the piezoelectric voltage coefficient is significantly higher than that without the oxide additive.

In addition, in the case of dielectric constant, when the oxide additive is added, it can be observed that the dielectric constant is higher than when it is not added.

The mechanical quality factor (Qm) refers to the ratio of energy accumulated during the exchange of electrical energy and mechanical energy. If the value is low, degradation occurs quickly. In this case, deterioration may lead to deterioration of the material and deterioration of the quality. As a result of the experiment, the mechanical quality factor of the oxide additive is shown to be relatively higher than that of the additive, and the piezoelectric properties are significantly improved due to the oxide additive. Can be.

The piezoelectric characteristics are not limited to the planar vibration mode of a disk-shaped piezoelectric ceramic vibrator, and oxides are the same as in the case of the planar vibration mode in other vibration modes used for longitudinal longitudinal vibration, thickness sliding vibration, and oscillator. The additive has excellent piezoelectric properties.

1 is a graph showing the results of the X-ray diffraction experiment according to the oxide additive of the lead-free piezoelectric ceramics of the present invention.

2 is a graph showing the thermal shock test results of the lead-free piezoelectric ceramics of the present invention.

FIG. 3 is a graph showing the change in temperature of the T _{o -t} phase transition for each type of oxide additive for a lead-free piezoelectric ceramic according to an embodiment of the present invention.

4 is a perspective view and a cross-sectional view of a piezoelectric ceramic vibrator manufactured by the present invention.

Claims (6)

delete delete delete Having a perovskite (Perovskite) crystal _{structure, {Li x (K 0 .5} Na 0 .5) 1-x} NbO 3 A first step of weighing and preparing a raw material powder to obtain a lead-free piezoelectric ceramic having a composition of (0.01 ≦ x ≦ 0.03); A second step of preparing a primary powder by mixing, pulverizing and then calcining the raw powder; On the primary powder A third step of preparing a secondary powder by adding 0.2 to 1.0 wt% of at least one of Fe ₂ O ₃ , Bi ₂ O ₃ , V ₂ O ₅ , MnO _2, or ZnO, mixing, and grinding; Adding a binder to the secondary powder and pressing to form a specimen; A fifth step of heating the specimen to volatilize and sinter the binder; And After polarizing the sintered specimen, a method of producing a lead-free piezoelectric ceramics is carried out in a sixth step of heat treatment at 100 ℃ ~ 200 ℃. The method of claim 4, wherein The second step is Preparing a primary powder by mixing and pulverizing the raw powder and then calcining at a temperature range of 750 ° C. to 950 ° C. for 4 hours to 6 hours; Method for producing a lead-free piezoelectric ceramics, characterized in that. The method according to claim 4 or 5, The fifth step is Heating the specimen to volatilize the binder and sintering at a temperature ranging from 900 ° C. to 1100 ° C .; Method for producing a lead-free piezoelectric ceramics, characterized in that.

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