JP2007261863A - Piezoelectric ceramic composition and piezoelectric ceramic - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition correspondable to reflow and containing potassium-sodium-lithium niobate as a main component, and to provide a piezoelectric ceramic formed of the composition. <P>SOLUTION: The piezoelectric ceramic is obtained from its composition containing potassium-sodium-lithium niobate, calcium titanate and bismuth ferrate as main components. The ceramic has a high electromechanical coupling coefficient, particularly a high piezoelectric constant g<SB>33</SB>, has no discontinuous part corresponding to a secondary phase transition in the temperature variation rate of resonant frequency, that of antiresonant frequency and that of piezoelectric constant g<SB>33</SB>in the temperature range of from -40 to +150°C, and also has excellent heat resistance. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric ceramic composition and a piezoelectric ceramic, and more particularly to a piezoelectric ceramic composition and a piezoelectric ceramic useful as piezoelectric ceramics for resonators such as piezoelectric sensors, piezoelectric ceramic filters, and piezoelectric ceramic oscillators.

As a piezoelectric ceramic used for a piezoelectric ceramic element such as a piezoelectric ceramic filter, piezoelectric ceramic composition composed mainly of lead zirconate titanate _{(Pb (Ti X Zr 1-} X) O 3) or lead titanate (PbTiO ₃₎ Is widely used.

  However, piezoelectric ceramics mainly composed of lead zirconate titanate or lead titanate have a low melting point and are likely to evaporate during firing, and the composition varies depending on the amount of evaporation. There was a problem to do.

For example, at least the following two are exemplified as the alkaline niobate-based piezoelectric ceramic. Among the niobate-based piezoelectric ceramics, sodium niobate (NaNbO ₃ ) (see, for example, Non-Patent Document 1) is an oxide having a perovskite (ABO ₃ ) type crystal structure. Piezoelectric ceramics exhibit ferroelectricity only at temperatures lower than around −133 ° C., and do not exhibit piezoelectricity in the range of −20 to + 80 ° C., which is a general operating temperature of piezoelectric resonator and oscillator materials. Cannot be used as

In addition, some piezoelectric ceramics mainly composed of potassium niobate / sodium / lithium (K _x Na _y Li _z NbO ₃ ) have a large electromechanical coupling coefficient, and resonators such as a piezoelectric ceramic filter and a piezoelectric ceramic oscillator. There are materials that are considered promising as materials for use (see, for example, Patent Documents 1 and 2).
Japanese Patent Laid-Open No. 11-228225 Japanese Patent Laid-Open No. 11-228227

  However, the piezoelectric ceramics mainly composed of potassium niobate / sodium / lithium in Patent Documents 1 and 2 have a high Curie temperature (first-order phase transition) of about 200 ° C. or higher, but a temperature of about −40 to + 150 ° C. In the range, there is a secondary phase transition that undergoes a phase transformation from the low-temperature side ferroelectric phase to the high-temperature side ferroelectric phase. Since there is a discontinuous portion in the change, large temperature hysteresis and characteristic deterioration are likely to occur, and this is an essential problem that cannot cope with reflow, which has been a major obstacle in practical use.

  Therefore, an object of the present invention is to provide a piezoelectric ceramic composition and a piezoelectric ceramic mainly composed of potassium, sodium niobate, lithium, and reflow capable.

The piezoelectric ceramic composition of the present invention includes (1) potassium niobate / sodium / lithium, calcium titanate, and bismuth ferrate. The piezoelectric ceramic composition was the (2) the potassium sodium lithium niobate _{(K x Na y Li 1-} x-y) NbO 3, CaTiO 3 the calcium titanate, BiFeO ₃ and bismuth ferrite Occasionally, the potassium sodium-lithium and calcium titanate niobate and the bismuth ferrite _{(1-a-b) (} K x Na y Li 1-x-y) NbO 3 + aCaTiO 3 + bBiFeO 3, 0 <a It is desirable that ≦ 0.15, 0 <b ≦ 0.1, 0 <x ≦ 0.18, and 0.8 <y <1.

The piezoelectric ceramic of the present invention is (3) obtained by firing the above piezoelectric ceramic composition, has an electromechanical coupling coefficient k ₃₃ of 30% or more, and a piezoelectric g ₃₃ constant of 20 × 10 ⁻³ V / N is equal to or higher than N, and at least one of a temperature change rate of the resonance frequency, a temperature change rate of the anti-resonance frequency, and a temperature change rate of the piezoelectric g ₃₃ constant in a temperature range of −40 to + 150 ° C. is 2% / ° C. It changes in the following.

According to the present invention, a piezoelectric ceramic composition mainly composed of potassium, sodium, and lithium niobate containing Ca, Ti, Bi, and Fe oxides has a specific composition, so that −40 to 40 In the temperature range of + 150 ° C., the temperature change rate of the resonance frequency, the temperature change rate of the anti-resonance frequency, and the temperature change rate of the piezoelectric g ₃₃ constant are eliminated, and the piezoelectric characteristics are stabilized. Can cope with reflow. That is, the Na-rich composition system of (NaKLi) NbO ₃ has an orthorhombic crystal structure, has a second-order phase transition in a temperature range of −40 to + 150 ° C., and has a Curie temperature of about 200 to 400 ° C. It is.

In contrast, by introducing calcium titanate and BiFeO ₃ , different crystals were combined and dissolved in (NaKLi) NbO ₃ , resulting in a phase transition temperature of −40 to + 150 ° C. The temperature change of the elastic constant and the piezoelectric g ₃₃ constant can be out of the range, and hysteresis is eliminated in the temperature range, and the characteristics can be stabilized. That is, there is no second-order phase transition when the elastic constant is continuous and there is no portion of the piezoelectric g ₃₃ constant that changes discontinuously near room temperature.

The piezoelectric ceramic composition of the present invention is characterized by containing potassium niobate / sodium / lithium, calcium titanate, and bismuth ferrate. Its composition, the potassium niobate sodium-lithium _{(K x Na y Li 1-} x-y) NbO 3, the calcium titanate CaTiO _3, when the bismuth ferrate and BiFeO _3, wherein niobate Potassium / sodium / lithium, calcium titanate and bismuth ironate are (1-ab) (K _x Na _y Li _1-xy ) NbO ₃ + aCaTiO ₃ + bBiFeO ₃ 0 <a ≦ 0.15, 0 < It is desirable that b ≦ 0.10 <x ≦ 0.18 and 0.8 <y <1.

  The compound represented by the above composition formula is adjusted to have the above composition by using oxides of K, Na, Li, Nb, Ti, Ca and Fe contained therein, so that most of the impurities after firing are obtained. A piezoelectric ceramic composed of a substantially single phase that cannot be seen can be formed.

That is, the piezoelectric ceramic composition of the present invention, the potassium niobate sodium-lithium _{(K x Na y Li 1-} x-y) NbO 3, for a particular composition of Na-rich side, CaTiO ₃ and BiFeO ₃ DOO by forms a perovskite crystal structure to compound in a complex manner, the electromechanical coupling factor is high, particularly large piezoelectric g ₃₃ constant, and, in the temperature range of -40 to + 0.99 ° C., the piezoelectric g ₃₃ constant Is a continuous (FIG. 1), can suppress the second phase transition showing a discontinuous change (FIG. 2), and can obtain a piezoelectric ceramic having excellent piezoelectric g ₃₃ constant temperature stability and excellent heat resistance. Can do. Here, the continuous change of the piezoelectric constant means that the piezoelectric g ₃₃ constant changes at 0.2% / ° C. or less. In the present invention, it is important that the piezoelectric g ₃₃ constant changes at 0.2% / ° C. or less. On the other hand, the discontinuous change means an abrupt change of the piezoelectric g ₃₃ constant as shown in FIG. That is, in the temperature range of −5 ° C. to 40 ° C., the piezoelectric g ₃₃ constant is changed by 12%. In the present invention, the piezoelectric g ₃₃ constant change rate is 0.27% / ° C. That's it.

The piezoelectric ceramic composition of the present invention, in _{particular, 1-a-b (K} x Na y Li 1-x-y) NbO 3 + aCaTiO 3 + bBiFeO 3, 0.01 <a ≦ 0.12,0.01 < It is desirable that the main component is a composition in the range represented by b ≦ 0.09, 0 <x ≦ 0.18, and 0.8 <y <0.98.

In the above specific composition range, the electromechanical coupling coefficient k ₃₃ is 30% or more, the piezoelectric g ₃₃ constant is 20 × 10 ⁻³ V / N or more, and the temperature change rate of the resonance frequency, For at least one of the temperature change rate of the resonance frequency and the piezoelectric g ₃₃ constant, a discontinuous portion called a second-order phase transition does not exist in the temperature range of −40 to + 150 ° C., and a piezoelectric ceramic having excellent piezoelectric characteristics can be formed. .

In the present invention, it is important to add CaTiO ₃ that is an ABO ₃ type perovskite structure compound to potassium niobate / sodium / lithium (K _x Na _y Li _1-xy ) NbO ₃ . For example, in the case of other ABO ₃ type perovskite structure compounds such as BaTiO ₃ , even if BiFeO ₃ is added, the temperature change rate of the resonance frequency, the temperature change rate of the antiresonance frequency, or the piezoelectric g ₃₃ constant as in the present invention. For at least one of them, a piezoelectric ceramic that does not have a discontinuous portion called a second-order phase transition in a temperature range of −40 to + 150 ° C. cannot be formed. The difference is not clear, but (K _x Na _y Li _1-xy ) NbO _{3 in} which CaTiO ₃ and BiFeO ₃ are combined in solid solution is the phase transition temperature between the ferroelectric and the paraelectric Is approximately −173 ° C., which is presumed to be due to the absence of structural phase transition at −40 ° C. to + 150 ° C., which is normally used.

Further, a composite solution of CaTiO ₃ and BiFeO ₃ in (K _x Na _y Li _1-xy ) NbO ₃ has the advantage that the porcelain can be densified, and the temperature is generally increased. It is excellent in stability and can be used in practice.

On the other hand, when CaTiO ₃ is introduced alone into potassium niobate / sodium / lithium (K _x Na _y Li _1-xy ) NbO ₃ , the piezoelectric g ₃₃ has a high Curie temperature of 200 ° C. or higher. Although it has the effect of increasing the constant, it is difficult to obtain a dense sintered body, and since it is a process for producing a sintered body using an apparatus such as a hot press, it has been used at low cost. For example, there is a problem that it cannot be replaced with a component such as a PZT piezoelectric sensor.

Furthermore, when BiFeO ₃ is introduced alone into potassium niobate / sodium / lithium (K _x Na _y Li _1-xy ) NbO ₃ , there is an effect of increasing the piezoelectric g ₃₃ constant by introducing a small amount. However, in the range of −40 to + 150 ° C., there is a problem that the use temperature is limited because there is a discontinuous portion called second order phase transition.

Thus, CaTiO ₃ and BiFeO ₃ are converted into 1-ab (K _x Na _y Li _1-xy ) NbO ₃ + a (Bi _0.5 Na _0.5 ) TiO ₃ + bBiFeO ₃ , 0 <a ≦ 0. 15 and 0 <b ≦ 0.10, 0 ≦ x ≦ 0.18, and 0.8 <y <1 so that the piezoelectric characteristics can be used in a wide temperature range by adjusting the composition. In this way, the Curie temperature of the piezoelectric ceramic of the present invention is higher than 280 ° C. which is a reflowable temperature, the electromechanical coupling coefficient k ₃₃ is 30% or more, and the piezoelectric g ₃₃ In particular, (1-ab) (K _x Na _y Li _1-xy ) NbO _{3 in} terms of making the constant 20 × 10 ⁻³ V / N or more and eliminating the second-order phase transition. _{+ aCaTiO 3 + bBiFeO 3, 0} . The main component is a composition in a range represented by 1 <a ≦ 0.12, 0.01 <b ≦ 0.09, 0 <x ≦ 0.18, 0.8 <y <0.98. desirable.

The piezoelectric ceramic of the present invention obtained by firing the piezoelectric ceramic composition described above, in the electromechanical coupling coefficient k ₃₃ of 30% or more, still more piezoelectric g ₃₃ constant is 20 × 10 -3 ^{V / N} or more In addition, the secondary phase transition is not included in the range of −40 to + 150 ° C. and good characteristics are exhibited. By using such a piezoelectric ceramic composition, a piezoelectric ceramic element such as a piezoelectric ceramic filter or a piezoelectric ceramic oscillator that can cope with reflow and has excellent piezoelectric characteristics can be produced.

As a starting material, K ₂ CO ₃ , Na ₂ CO ₃ , Li ₂ CO ₃ , CaCO ₃ , Nb ₂ O ₅ , TiO ₂ , Fe ₂ O ₃ , and powder are used, and the composition formula of the piezoelectric ceramic is (1-a _{-b) (K x Na y Li} 1-x-y) NbO 3 + aCaTiO 3 + bBiFeO 3, 0 <a ≦ 0.16,0 <b ≦ 0.1,0 ≦ x ≦ 0.19,0.79 < Weighed so that the composition shown in Table 1 was obtained when y <1.

Next, this mixture was wet mixed in a ball mill for 20 hours using IPA (isopropyl alcohol) and ZrO ₂ balls. Next, after drying this mixture, it was calcined at 900 to 1100 ° C. for 3 hours in the air, and the calcined product was again finely pulverized by the ball mill. Thereafter, the pulverized material was mixed with a binder such as polyvinyl alcohol (PVA) and granulated.

  The obtained powder was molded into a cylindrical shape of φ3 × thickness 12 mm at a pressure of 200 MPa. The molded body was fired at 1000 to 1250 ° C. for 2 hours in the air. As a result of measuring and identifying the XRD pattern of the obtained piezoelectric ceramic, it was found that all were composed mainly of perovskite crystals. That is, the piezoelectric ceramic of the present invention has a composite perovskite crystal structure composed of a three-component system. For example, from the X-ray diffraction diagram of Sample 1, it was confirmed that the piezoelectric ceramic had a single perovskite crystal structure. .

Further, after forming silver electrodes on both sides of φ3 mm of this porcelain, a polarization treatment was performed by applying a DC electric field of 4 to 7 kV / mm for 10 to 30 minutes in silicon oil at 80 ° C. Then, according to EMAS established by the Japan Electronic Materials Industry Association, the capacitance, resonance / antiresonance frequency and resonance resistance of these piezoelectric elements were measured using an impedance analyzer. From the measured values, the relative dielectric constant of the longitudinal vibration mode, the electromechanical coupling coefficient K ₃₃ , and the piezoelectric g ₃₃ constant were obtained. Furthermore, the temperature dependence of the resonance frequency and the temperature dependence of the piezoelectric g ₃₃ constant were investigated to investigate the second-order phase transition. The temperature change rate of the resonance frequency and the piezoelectric g ₃₃ constant was expressed as a change rate at each temperature from −40 ° C. to + 150 ° C. based on the value of 25 ° C.

Next, for each sample, the relative permittivity ε ₃₃ ^T / ε ₀ , the electromechanical coupling coefficient K ₃₃ , the temperature change of the piezoelectric g ₃₃ constant and the piezoelectric g ₃₃ constant, and the change of the resonance frequency and the anti-resonance frequency are measured, The discontinuities of the above characteristics were measured to investigate the presence or absence of secondary phase transition. The composition of the produced porcelain was subjected to ICP emission spectroscopic analysis using a solution obtained by mixing and melting the obtained piezoelectric ceramic with boric acid and sodium carbonate in hydrochloric acid and diluting a standard solution containing 1000 ppm of each element as a standard sample. Quantified. The results are shown in Tables 1 and 2.

In Tables 1 and 2, the sample numbers marked with * are outside the scope of the present invention. In Table 1, a sample satisfying all the conditions of 0 <a ≦ 0.15, 0 <b ≦ 0.1, 0 <x ≦ 0.18, 0.8 <y <1, that is, the sample number is marked with *. For all the samples according to the embodiments of the present invention that were not performed, the electromechanical coupling coefficient K ₃₃ was 30% or more, the piezoelectric g ₃₃ constant was 20 × 10 ⁻³ V / N or more, and − In a temperature range of 40 to + 150 ° C., a discontinuous portion corresponding to the second-order phase transition is suppressed (FIG. 1, sample No. 3), thus exhibiting good characteristics.

On the other hand, sample no. 19, the conditions of 0 <b ≦ 0.1, 0 <x ≦ 0.18, and 0.8 <y <1 are satisfied, but the conditions of a = 0 and 0 <a ≦ 0.1 are satisfied. In the unsatisfactory sample, the electromechanical coupling coefficient K ₃₃ is 30% or more and the piezoelectric g ₃₃ constant is 20 × 10 ⁻³ V / N or more, but a large secondary phase in the temperature range of −40 to + 150 ° C. It can be seen that a discontinuity corresponding to the transition is included.

However, the sample 19 as a base, satisfying all the conditions as a = 0.1, for example the sample 1, the sample 2, the electromechanical coupling coefficient _{K 33} is 30% or more, the piezoelectric _{g 33} constant is 20 × It is 10 ⁻³ V / N or more and does not include a discontinuous portion corresponding to the second-order phase transition in the temperature range of −40 to + 150 ° C.

  Further, for example, in Sample 1, it was confirmed that a discontinuous portion corresponding to the second-order phase transition was not confirmed in the temperature range of −40 to + 150 ° C., but in the behavior up to the Curie temperature higher than that, the relative permittivity As a result of investigating the temperature dependence, no discontinuous behavior of relative permittivity associated with the second-order phase transition was confirmed. Therefore, for example, in the case of sample 1, it was confirmed that the secondary phase transition was not included in the range from −40 to the Curie temperature (300 ° C.). For example, sample 1 has a high Curie temperature and can be mounted by reflow of an SMD (surface mount type electronic component). It can be possible to replace.

6 is a graph showing a temperature change rate of a piezoelectric g ₃₃ constant of sample 3. 4 is a graph showing a temperature change rate of a piezoelectric g ₃₃ constant of a sample 19.

Claims (3)

A piezoelectric ceramic composition comprising potassium niobate / sodium / lithium, calcium titanate, and bismuth ferrate. When (K _x Na _y Li _1-xy ) NbO ₃ is used as the potassium niobate / sodium / lithium, CaTiO ₃ is used as the calcium titanate, and BiFeO ₃ is used as the bismuth ferrate (1-ab). _{(K x Na y Li 1-} x-y) NbO 3 + aCaTiO 3 + bBiFeO 3
0 <a ≦ 0.15
0 <b ≦ 0.1
0 <x ≦ 0.18
0.8 <y <1
The piezoelectric ceramic composition according to claim 1 represented by: It is obtained by firing the piezoelectric ceramic composition according to claim 1, and has an electromechanical coupling coefficient k ₃₃ of 30% or more and a piezoelectric g ₃₃ constant of 20 × 10 ⁻³ V / N or more. In the temperature range of −40 to + 150 ° C., at least one change among the temperature change rate of the resonance frequency, the temperature change rate of the anti-resonance frequency, and the temperature change rate of the piezoelectric g ₃₃ constant changes at 2% / ° C. or less. A piezoelectric ceramic.

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