KR910007119B1 - Oxide piezo-electric materials and its manufacturing method - Google Patents

Abstract

An oxide piezoelectric material composed of (Pb1-xCax) [(Li1/4 Fe1/4 W1/2) 0.02Ti0.98 O3 + Y mol% MnO [= 0.15-0.25; y= 1-2 is produced by (a) mixing a raw oxide powder of PbO, TiO2, CaCO3, WO3, LiCO3 and Fe2O3 by the ball-mill, (b) firing the mixt. at 850 deg.C and 950 deg.C for 4hr, (c) pressure-molding the fired powder and a binder at 1 ton/cm2, (d) calcining the molded material at 1060-1100 deg.C for 1hr, (e) forming an electrode on the both sides of the calcined material, and (f) polarizing it. The piezoelectric material is useful as a material for piezoelectric devices in the high frequency region.

Description

Oxide piezoelectric material and its manufacturing method

1 is a graph showing changes in the coupling coefficient (Kt) of the thickness vibration and the coupling coefficient (Kp) of the radial vibration according to the calcium content of the present invention.

2 is a graph showing a change in permittivity (ε) phase transition temperature (Tc) according to the calcium content of the present invention.

3 is a graph showing a change in the coupling coefficient (Kt) according to the polarization field of the present invention.

4 is a graph showing a change in the temperature coefficient (TCF) of the resonant frequency according to the calcium content of the present invention.

The present invention relates to an oxide piezoelectric material suitable for a piezoelectric element material in a high frequency region mainly composed of lead titanate (PbTiO ₃ ), and a manufacturing method thereof.

As a conventional oxide piezoelectric material, the binary system of PbZrO ₃ -PbTiO ₃ of U.S. Patent No. 2,708.244 is well known, which employs lead zirconate titanate [Pb (Zr, Ti) O ₃ ] in which PbTiO ₃ and PbZrO ₃ have almost the same composition. Compared to BaTiO ₃ piezoelectric material, the piezoelectric material exhibits excellent piezoelectric properties in a relatively wide temperature range, and in particular, piezoelectric properties are known to be improved by addition of various additives including NbO, WO ₃ , and the like.

의 기본조성으로 이루어진 3성분계 고용체중에 있어서 Pb일부를 Ba나Sr 등으로 치환시킴과 아울러 In₂O₃등의 첨가물을 미량 첨가한 산화물 압전재료가 개시되어 있다.Recently, a three-component oxide piezoelectric material (hereinafter referred to as PZT system) in which a composite perovskite compound is dissolved in Pb (Zr, Ti) O ₃ has been developed, and thus, an ultrasonic vibrator, a ceramic filter element, and a pressure sensor element. , Ignition devices, surface wave devices, and the like, and for example, JP-A-57-208183 discloses PbTiO ₃ and PbZrO ₃ and composite perovskite compounds.

An oxide piezoelectric material is disclosed in which a portion of Pb is replaced with Ba or Sr in a three-component solid solution composed of a basic composition, and a small amount of an additive such as In ₂ O _{3 is} added.

두께진동을 고주파에서 사용하는 경우 경방향 진동의 결합계수의 오버톤(overtone)에 의한 의사진동(擬似振動)의 발생을 초래하는 문제점이 있다.However, such a conventional PZT oxide piezoelectric material exhibits a high dielectric constant of 1000 or more, so that the impedance of the piezoelectric element itself is lowered when used at high frequency, which makes it difficult to match impedance with an external circuit. As the material has almost the same coupling coefficient (Kt) of thickness vibration and coupling coefficient (Kp) of radial vibration, as a result, the anisotropy of vibration between thickness direction and radial direction is small.

When the thickness vibration is used at a high frequency, there is a problem of causing pseudo-movement due to overtone of the coupling coefficient of the radial vibration.

Therefore, piezoelectric elements used at high frequencies preferably have a low dielectric constant and a large ratio of the coupling coefficient (Kt) of the thickness vibration to the coupling coefficient (Kp) of the radial vibration. In view of the above, PbTiO ₃ has a high dielectric constant. It has a small value of about 200, and the coupling coefficient (Kp) of the radial vibration is very small compared to the coupling coefficient (Kt) of the thickness vibration, so that the impedance matching at high frequency is easy and the anisotropy of the vibration is high. However, the PbTiO ₃ has a very high anisotropy (c / a) of 1.063 in the lattice constant, resulting in cracks and spontaneous collapse due to the internal stress generated during phase transition. It is impossible to manufacture a sintered compact having

In addition, the sintered body of PbTiO ₃ must be polarized by applying an electric field of 100 kV / cm or more at a temperature of 200 ° C. or higher, so there is a risk of disintegration. Therefore, the polarization condition is very difficult, and as time passes after sintering, cracks and spontaneous collapse of the sintered body are sintered. Due to deterioration such as the occurrence of sintered body, it is difficult to manufacture a stable sintered body, which makes it difficult to put to practical use.

Degradation such as cracking and decay in the PbTiO _3- based sintered body is closely related to the ratio of PbO / TiO in view of the grain size and the interparticle bonding relationship in the grain broundary. Turned out.

That is, when PbO / TiO ₂ > 1 is excessively present, precipitated phases of PbO are generated at grain boundaries, which weakens the bond strength between particles and falls short of the bond strength between grain boundaries that can resist internal deformation, and PbO / TiO ₂ <0.98. When the abnormal growth of the particles occurs, the grain boundary area is reduced, resulting in a decrease in the bond strength between the particles. Therefore, in order to obtain a high-density stable sintered compact with little change over time and excellent piezoelectric properties, the composition of the sintered compact must be accurately maintained at 0.98 ≦ PbOTiO ₂ ≦ 1.00.

At this time, in order to maintain the ratio of PbO and TiO within the above range, above all, the sintering temperature should be kept low.

Because, when the sintering temperature is high, there is a problem that the volatilization of PbO is increased, making it difficult to control PbO / TiO. Also, the growth rate of the particles is sensitive to the sintering temperature, so that the abnormal growth of the particles rapidly growing at a certain temperature or more is difficult. There is a problem that occurs.

The present invention has been made in view of the above-mentioned problems of the conventional PbTiO ₃ piezoelectric material, and has a low sintering motion at high frequency, which is suitable for piezoelectric element materials in the high frequency region, and has a compact structure due to low sintering temperature. It is an object of the present invention to provide an oxide piezoelectric material having an easy polarization operation and having an improved surface wave temperature coefficient and a method of manufacturing the same.

Such oxide piezoelectric material of the present invention contains lead titanate (PbTiO ₃ ) as a main component and contains a small amount of calcium (Ca), lithium (Li), iron (Fe), tungsten (W), etc., and a small amount of MnO is added as a minor component. Lead titanate (PbTiO ₃ ) -based piezoelectric material, in which part of Pb is replaced with calcium (Ca) having a large ion radius, and Ti is replaced with lithium (Li), iron (Fe), and tungsten (W). At this time, the valence of the element to be substituted is calcium divalent, lithium monovalent, iron trivalent, and tungsten hexavalent.

The composition of the oxide piezoelectric material of the present invention,

Where x is 0.15 ≦ x ≦ 0.25 and y is 1 ≦ y ≦ 2.

에서 x의 값을 0.15≤x≤0.25의 범위로 한정한 이유는, X＜0.25인 경우에는 재료의 유전율(ε)이 증대됨과 아울러 150ppm/℃이상의 높은 온도계수를 나타내게 되어 표면파 소자용 재료로서의 응용에 부적할 뿐만 아니라 고주파에서의 임피던스 정합에 어려움이 있기 때문이며, 또한 x＜0.15인 경우에는 상기한 문제점이 발생된다.Basic composition of the present invention

The reason for limiting the value of x to 0.15≤x≤0.25 is that in the case of X <0.25, the dielectric constant (ε) of the material is increased and high temperature coefficient of 150ppm / ° C or higher is used. This is because not only is unsuitable but also difficulty in impedance matching at high frequencies, and when x &lt; 0.15, the above problem occurs.

In addition, the content of MnO added as a minor component is limited to 1-2 mol%. When the content of MnO is less than 1 mol%, the original purpose of adding a minor component, that is, the effect of improving the sinterability and polarization condition of PbTiO ₃ ceramic It is hardly expected, and if the addition amount is 2 mol% or more, the polarization condition of the ceramic becomes difficult due to the remarkable increase in conductivity.

The oxide piezoelectric material of the present invention is produced by a general powder metallurgy method.

That is, first, raw material powder oxides such as PbO, TiO ₂ , CaCO ₃ , WO ₃ , LiCO ₃ , Fe ₂ O ₃ , are precisely weighed at an appropriate ratio and mixed by a ball mill or the like.

Next, the mixture was calcined at 850 ° C. and then calcined again at 950 ° C. for 4 hours, and then pulverized by a ball mill or the like. Then, the pulverized calcined powder was press-molded at a pressure of 1 ton / cm 2 under the addition of a binder and then 1060-1100. It bakes for 1 hour at the temperature of ° C.

In the sintered body thus produced, electrodes are formed on both sides through a general method, and polarization is performed by applying a 60 mA / cm DC electric field to the electrodes at 120 ° C.

In the manufacturing process of the oxide piezoelectric material of the present invention, the initial stage, that is, the mixing and calcining process of the raw material powder has an important influence on obtaining a stable sintered compact, so it should be particularly careful.

This is because abnormal growth of particles easily occurs when the composition of the mixed raw powder is uneven or incomplete decomposition of carbonate during the calcination process, and it is difficult to manufacture a sintered compact having a stable single-phase perovskite structure.

In other words, the specific gravity of PbO and CaCO ₃ LiCO ₃ when mixing the raw powder is not easy to mix according to the specific gravity difference, and the residual CaCO ₃ appears even though the first heat treatment is performed for a long time. Since the perovskite structure cannot be obtained, the presence of undecomposed CaCO ₃ during the first calcination causes the nonuniformity of the composition to be intensified, leading to abnormal growth of the particles during sintering, thereby causing spontaneous collapse of the sintered body.

Therefore, in the present invention, in order to rule out the problems caused by the presence of such residual CaCo _3, the second calcination is performed after the first calcination, so that CaCo ₃ is completely decomposed to form a stable single-phase powder. By performing the sintered compact to obtain a sintered compact that does not cause deterioration and spontaneous collapse.

The effect of the oxide piezoelectric material of the present invention prepared by such a manufacturing method is as follows.

First, in the case of the conventional PZT-based piezoelectric material, there is a problem in the application to the high-frequency device according to the generation of pseudo copper as described above, but the piezoelectric material of the present invention has a large coupling coefficient Kt of 50% or more in the thickness direction. In contrast, the contention coefficient (Kp) in the radial direction is less than 5%, so that almost no photodynamic movement occurs at high frequencies, so it is not only suitable as a material for high frequency devices, but also ultrasonic waves using conventional PZT materials. Disadvantages of shape enlargement and cross-coupling, which are disadvantages of the probe element, are solved by the use of the present material.

Further, since the present invention materials can be substituted for part of the PZT by Ca, and lowering the firing temperature than the conventional PZT-based material according to the O ₃ the baking temperature is low Pb (Li Fe W) on a part Sikkim employed PbTiO ₃ Significantly improves the sinterability of the system materials, making it possible to manufacture ceramics with dense and small pores that can be used for surface wave substrate materials, and polarization operation is facilitated as some Pb is replaced with Ca. Coupling coefficient (Kt) in sufficient thickness direction can be obtained under polarization condition of / cm and large oscillator can be manufactured by eliminating the risk of discharge collapse during polarization.

화합물을 고용시킴에 따라 압전재료의 소성온도를 저하시킴과 더불어 부성분으로서 MnO를 첨가하여 소성온도를 1060-1100℃로 저하시킴으로써 PbO의 휘발을 방지하여 PbO 휘발에 따른 조성변화를 방지하게 된다.Furthermore, the present invention is a composite perovskite for promoting sintering

As the compound is dissolved, the firing temperature of the piezoelectric material is lowered, and MnO is added as a subcomponent to lower the firing temperature to 1060-1100 ° C. to prevent volatilization of PbO, thereby preventing a composition change due to volatilization of PbO.

In addition, in the conventional PbTiO ₃ material, the temperature coefficient of the resonance frequency is negative (-), and it is impossible to obtain a temperature coefficient value of -20 ppm / ° C or lower due to the change of additives or solid solution, but the present invention is a part of Pb. Substitution of 15-20 mole% of Ca enables reversal of the temperature coefficient, which enables the production of materials having a temperature coefficient within ± 20 ppm / ° C. (including a temperature coefficient of 0 ppm / ° C.) as well as addition of MnO. As a result, the sinterability, polarization characteristics, and resonant frequency characteristics with time are improved.

Embodiments of the present invention are as follows.

의 조성식을 갖는 압전재료에 있어서,PbTiO is the main ingredient and contains a small amount of Ca, Li, Fe, W

In a piezoelectric material having a composition formula of

x = 0.15-0.25

y = 1-2

The basis weight exactly the raw material powder, such as that PbO, TiO _2, CaCO _3, MnCO _3, WO _3, LiCO ₃ and FeCO ₃ The composition range is mixed in a ball mill and then, the mixture was first calcined for 2 hours at 850 ℃ Subsequently, the resultant was calcined at 950 ° C. for 2 hours and then pulverized again by a ball mill. The pulverized powder was press-molded at a pressure of 1 ton / cm 2 and then calcined at 1060-1100 ° C. for 1 hour to obtain a sintered body.

This sintered body was cut and polished into a disk of 10ψ × 0.5㎜ and polarized under the condition of 120 ℃ and 60㎸ / cm with electrodes attached on both sides, followed by the standard circuit method shown in Proc.IRE.Vol 137, 1378-1395, etc. The piezoelectric properties of the sintered bodies having different composition ratios were measured. Table 1 below shows the composition and manufacturing conditions of the sintered bodies of the present invention, and Table 2 shows the piezoelectric characteristics of the sintered bodies.

TABLE 1

TABLE 2

In Table 2, ε is the dielectric constant (1㎑, 25 ℃), tanδ is the dielectric loss (25 ℃), Kt is the coupling coefficient of thickness vibration (%), Kp is the coupling coefficient of radial vibration (%), and Qm is The mechanical quality factor, Tc, is the phase transition temperature, TCF is the temperature coefficient of the resonance frequency (ppm / ° C), and d ₃₃ and g ₃₃ are piezoelectric constants.

FIG. 1 is a graph showing changes in electromechanical coefficients Kt and Kp according to the substitution amount of calcium (Ca) in the sintered bodies of Examples 1 to 4, and as the content of calcium (Ca) increases as shown in FIG. The bond coefficient (Kt) of the thickness vibration gradually increased to the maximum at 25 mol%, while the bond coefficient (Kp) of the radial vibration decreased rather as the calcium (Ca) content increased. The anisotropy of the coupling coefficient is very large, and it can be seen that the material of the present invention is suitable as a material of the probe for the high frequency region and the ultrasonic diagnostic apparatus.

2 is a graph showing the change in dielectric constant (ε) and phase transition temperature (Tc) according to the calcium content of the sintered body of the present invention. As the content of calcium increases, the dielectric constant increases almost proportionally, and the phase transition temperature increases with increasing amount of calcium substitution. It is gradually lowering accordingly.

Next, FIG. 3 shows the change in the coupling coefficient (Kt) according to the polarization electric field when the substitution amount of calcium is 17 mol%. When the electric field of 40 포화 / ㎝ or more is applied, the individual domains are saturated. .

4 is a change in the temperature coefficient (20 ℃-80 ℃) of the resonant frequency according to the amount of calcium substitution of the material of the present invention, a material having a temperature coefficient of ± 20ppm / ℃ in the vicinity of 15-20 mol% A temperature coefficient of 0 ppm / ° C is obtained at around 17 mole percent.

As can be seen from the above examples and drawings, the material of the present invention is useful as various piezoelectric element materials applied in high frequency region because the dielectric constant is low as 200 or less, the temperature coefficient is excellent and the anisotropy of vibration is large.

Claims (2)

PbTiO ₃ as a main component,

With the basic composition x = 0.15-0.25 y = 1-2 Oxide piezoelectric material, characterized in that the composition range.

As x = 0.15-0.25, y = 1-2, the composition is calcined first at 850 ° C. for 2 hours, then calcined at 950 ° C. for 4 hours, and then pulverized and press-molded, and then sintered at 1060-1100 ° C. A method for producing an oxide piezoelectric material.

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