JP4684089B2 - Piezoelectric ceramic composition and piezoelectric ceramic - Google Patents

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, wide piezoelectric ceramic composition composed mainly of lead zirconate titanate (Pb (Tix Zr1-x) O 3) or lead titanate (PbTiO ₃₎ It is used.

  In this way, the presence of lead is indispensable for the enhancement of the functionality of piezoelectric ceramics represented by lead zirconate titanate, but in recent years, the harmfulness of lead has been pointed out in terms of the effect on the human body, Although the lead component contained in the crystallized lead zirconate titanate exists in a relatively stable state compared to other lead-containing products contained in other amorphous states, from the viewpoint of environmental conservation However, a piezoelectric ceramic containing as little lead as possible has been demanded.

  Further, a piezoelectric ceramic mainly composed of lead zirconate titanate or lead titanate has a problem that the uniformity of the product is lowered due to evaporation of lead oxide in the manufacturing process.

  Therefore, in order to solve the above-mentioned problems caused by containing a lead component, a new lead-free piezoelectric ceramic is now required as a material for piezoelectric resonators and oscillators. Among these, alkaline niobate piezoelectric ceramics are attracting attention as ceramic materials that do not contain lead and exhibit high piezoelectricity.

Examples of the alkali niobate-based piezoelectric ceramic include at least the following two. Among the piezoelectric ceramic of the alkali niobate-based, sodium niobate (NaNbO ₃ for example, see Non-Patent Document 1) is an oxide having a crystal structure of perovskite (ABO ₃₎ type, in itself, -133 Ferroelectricity is exhibited only at temperatures lower than around 0 ° C., and piezoelectricity is not exhibited in the range of −20 to 80 ° C., which is a general use temperature of piezoelectric resonator and oscillator materials,
Cannot be used as a piezoelectric ceramic.

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).
Japan Journal of Applied Physics, p.322, vol.31, 1992 Japanese Patent Laid-Open No. 11-228225 Japanese Patent Laid-Open No. 11-228227

  However, the piezoelectric ceramic mainly composed of potassium, sodium, and niobate described above has a high Curie temperature (first-order phase transition) of about 200 ° C. or higher, but a low temperature in a temperature range of about −40 to 150 ° C. Since there is a secondary phase transition that transforms from the ferroelectric phase on the high-temperature side to the ferroelectric phase on the high-temperature side, there is a discontinuity in changes in piezoelectric characteristics and resonance frequency under temperature cycles that pass through the secondary phase transition. Since there is a portion, there is a problem that large temperature hysteresis and characteristic deterioration are likely to occur. These large temperature hysteresis and characteristic deterioration in piezoelectric ceramics mainly composed of potassium, sodium, and lithium niobate are essential problems such as inability to cope with reflow in the mounting process, and thus there are significant restrictions in practical use. .

Accordingly, the present invention comprises a piezoelectric ceramic composition having stable piezoelectric characteristics, such as potassium niobate, sodium, and lithium niobate as the main components, and the temperature change rate of the resonance frequency, the temperature change rate of the antiresonance frequency, and the temperature change rate of the piezoelectric g ₃₃ constant. The object is to provide an object and a piezoelectric ceramic.

The piezoelectric ceramic composition of the present invention, was (1) potassium sodium lithium niobate _{(K x Na y Li 1-} x-y) NbO 3, SrTiO 3 strontium titanate, BiFeO ₃ and bismuth ferrite when, with the potassium niobate, sodium-lithium, and the strontium titanate, and the bismuth _{ferrite, (1-a-b)} (K x Na y Li 1-x-y) NbO 3 + aSrTiO 3 + BBiFeO ₃
0 <a ≦ 0.1
0 <b ≦ 0.11
0 ≦ x ≦ 0.18
0.8 ≦ y <1
It is characterized by including in the range represented by.

The piezoelectric ceramic composition is (2 )
0 . 01 ≤ a ≤ 0.08
0.01 ≦ b ≦ 0.09
0 ≦ x ≦ 0. 075
0.8 ≤ y ≤ 0.98
Der Rukoto is desirable.

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 / and wherein the N or der Turkey.

According to the present invention, the piezoelectric ceramic composition mainly composed of potassium niobate / sodium / lithium is made Na-rich as described above, and Sr, Ti and Stabilized piezoelectric characteristics such as temperature change rate of resonance frequency, temperature change rate of anti-resonance frequency, temperature change rate of piezoelectric g ₃₃ constant, etc. by using a specific composition containing each oxide of Bi and Fe Can be.

That is, the Na-rich composition system of (NaKLi) NbO ₃ has an orthorhombic crystal structure, a secondary phase transition in the temperature range of −40 to 150 ° C., and a Curie temperature of about 200 to 400 ° C. It is.

Against this composition system, is introduced optimum amount of strontium titanate, further, by introducing the optimum amount of BiFeO ₃ consisting of rhombohedral (Curie temperature about 870 ° C.), (Na
To KLi) NbO ₃ , different crystals are combined and dissolved , and (1-ab) (K _x Na
_y Li _1-xy ) NbO ₃ + aSrTiO ₃ + bBiFeO ₃
0 <a ≦ 0.1
0 <b ≦ 0.11
0 ≦ x ≦ 0.18
0.8 ≦ y <1
As a result , the phase transition temperature is changed, and as a result, the temperature change of the elastic constant and the portion of the piezoelectric g ₃₃ constant that changes discontinuously near room temperature can be suppressed. 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.

When the piezoelectric ceramic composition of the present invention is potassium niobate / sodium / lithium (K _x Na _y Li _1-xy ) NbO ₃ , strontium titanate is SrTiO ₃ , and bismuth ferrate is BiFeO ₃ , said potassium niobate, sodium-lithium, and the strontium titanate, and the bismuth _{ferrite, (1-a-b)} (K x Na y Li 1-x-y) NbO 3 + aSrTiO 3 + bBiFeO 3
0 <a ≦ 0.1
0 <b ≦ 0.11
0 ≦ x ≦ 0.18
0.8 ≦ y <1
It is characterized by including in the range represented by.

The compound represented by the above composition formula is adjusted to have the above composition using the oxides of K, Na, Li, Nb, Ti, Sr and Fe contained therein, so that most of the impurities after firing 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 is composed of SrTiO ₃ and BiFeO ₃ with respect to a specific composition on the Na-rich side in potassium niobate / sodium / lithium (K _x Na _y Li _1-xy ) NbO ₃ . By forming a perovskite-type crystal structure so as to combine with each other, the electromechanical coupling coefficient is high, the piezoelectric g ₃₃ constant is particularly large, and the piezoelectric constant is not constant in the temperature range of −40 to 150 ° C. a second phase transition showing a continuous change can be suppressed, excellent temperature stability of the piezoelectric g ₃₃ constant, and it is possible to obtain an excellent piezoelectric ceramic heat resistance.

And the piezoelectric ceramic composition of the present invention is, in particular ,
0.01 ≤ a ≤ 0.08
0.01 ≦ b ≦ 0.09
0 ≦ x ≦ 0. 075
0.8 ≤ y ≤ 0.98
It is not to desirable as the main component composition is.

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, the temperature change rate of resonance frequency, With respect to at least one of the temperature change rate of the resonance frequency and the piezoelectric g ₃₃ constant, a piezoelectric ceramic having excellent piezoelectric characteristics can be formed without a discontinuous portion called a secondary phase transition in a temperature range of −40 to 150 ° C. .

In the present invention, it is important that the ABO ₃ type perovskite structure compound added to potassium niobate / sodium / lithium (K _x Na _y Li _1-xy ) NbO ₃ is SrTiO ₃ . For example, in the case of an ABO ₃ type perovskite structure compound such as BaTiO ₃ or CaTiO 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 as in the present invention. For at least one of the constants, 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. Although this is not clearly different from BaTiO ₃ or CaTiO ₃ , it is peculiar to SrTiO ₃ , and the phase transition temperature between the ferroelectric and the paraelectric is about −173 ° C., which is normally used −40 ° C. It is presumed to be due to the absence of a structural phase transition at ˜150 ° C.

_{Further, (K x Na y Li 1} -x-y) NbO 3 to SrTiO ₃ and BiFeO ₃ with a material obtained by adjusting the composition so as to compositely solid solution, advantage can be densified porcelain In general, it is excellent in temperature stability and can be actually used.

On the other hand, when SrTiO 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 −20 to 150 ° C., there is a problem that the use temperature is limited because there is a discontinuous portion called second order phase transition.

In this way, SrTiO ₃ and BiFeO ₃ are converted to 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. By adjusting the composition so that the relationship of 1, 0 <b ≦ 0.1 1 , 0 ≦ x ≦ 0.18, 0.8 ≦ y < 1 is satisfied, the piezoelectric material that can be used in a wide temperature range particularly in the present invention. A piezoelectric ceramic having excellent characteristics can be obtained.

In the range of 0 <a ≦ 0.10 in the piezoelectric ceramic represented by the above composition formula, when a exceeds 0.10, the electromechanical coupling coefficient K ₃₃ becomes smaller than 30%, and the piezoelectric g ₃₃ constant Becomes less than 20 × 10 ⁻³ V / N, making it difficult to use as a material for piezoelectric sensors, piezoelectric ceramic filters, piezoelectric ceramic oscillators, and the like. In the case of 0, there is a discontinuous portion called a second-order phase transition in the temperature range of −40 to 150 ° C., so that there is a discontinuous behavior in the temperature characteristics of the piezoelectric constant. Cannot be used in a wide temperature range.

0 <for the range of b ≦ 0.10, if b is more than 0.1, the electromechanical coupling coefficient K ₃₃ is smaller than 30%, it becomes difficult to use as a material such as a piezoelectric ceramic oscillator Because. In the case of 0, there is a discontinuous portion called a second-order phase transition in the temperature range of −40 to 150 ° C., so that there is a discontinuous behavior in the temperature characteristics of the piezoelectric constant. Cannot be used in a wide temperature range.

In the range of 0 ≦ x ≦ 0.18, when x exceeds 0.18, the electromechanical coupling coefficient K ₃₃ is less than 30%, and the piezoelectric g ₃₃ constant is less than 20 × 10 ⁻³ V / N. Further, it becomes difficult to use as a material such as a piezoelectric sensor, a piezoelectric ceramic filter, and a piezoelectric ceramic oscillator .

For the range of 0.8 ≦ <y <1, when y is less than 0.8, the second-order phase transition exists in the temperature range of −40 to 150 ° C. Since discontinuous behavior exists, it cannot be used in a wide temperature range. Further, when y = 1, the piezoelectricity is remarkably lowered, the electromechanical coupling coefficient K ₃₃ is smaller than 30%, the piezoelectric g ₃₃ constant is less than 20 × 10 ⁻³ V / N, and the piezoelectric sensor or the piezoelectric ceramic. Use as a material for a filter, a piezoelectric ceramic oscillator or the like becomes difficult.

For the above reasons, in the present invention, in particular, the Curie temperature 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 constant is 20 × 10 ⁻³ V / in the above N, and in that eliminate the second order phase transition, in _{particular, 1-a-b (K} x Na y Li 1-x-y) NbO 3 + aSrTiO 3 + bBiFeO 3 0.01 ≦ a ≦ 0.08, 0.01 ≦ b ≦ 0.09, 0 ≦ x ≦ 0. It is desirable that the main component is a composition in a range represented by 075 , 0.8 ≦ y ≦ 0.98.

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 Moreover, the secondary phase transition is not included in the range of −40 to 150 ° C., and good characteristics such that the Curie point exceeds 200 ° C. are exhibited. Using such a piezoelectric ceramic composition, piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators can be advantageously produced.

As the starting material, each powder of K ₂ CO ₃ , Na ₂ CO ₃ , Li ₂ CO ₃ , SrCO ₃ , Nb ₂ O ₅ , TiO ₂ , and Fe ₂ O ₃ was used, and the piezoelectric ceramic was represented by the composition formula 1- a _{-b (K x Na y Li 1} -x-y) Oite to _{NbO 3 + aSrTiO 3 + bBiFeO 3} , a, b, x and y are weighed so as to have the composition shown in Table 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 (FIG. 1: Sample 1). 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 permittivity 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 dielectric constant ε ₃₃ ^T / ε ₀ , electromechanical coupling coefficient K ₃₃ , piezoelectric g
₃₃ constant and piezoelectric g The temperature change of the ₃₃ constant and the change of the resonance frequency and the antiresonance frequency were measured, and the discontinuity part of the characteristic was measured to investigate the presence or absence of the 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, 0 <a ≦ 0.1,0 < b ≦ 0.1 1, 0 ≦ x ≦ 0.18,0.8 ≦ y < specimen meet all the conditions of 1 are all - 40 a state in which the discontinuous portion is suppressed corresponding to the second order phase transition at a temperature range of to 150 DEG ° C., shows good good properties.

In contrast, sample no. As shown in FIG. 19, although 0 <b ≦ 0.1 1 , 0 ≦ x ≦ 0.18, 0.8 ≦ y <1 are satisfied, since a = 0 , 0 <a ≦
In a sample that does not satisfy the condition of 0.1, 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 as shown in FIG. 6 and FIG. It can be seen that a discontinuous portion corresponding to a large second-order phase transition is included in a temperature range of −40 to 150 ° C.

Then, the sample 19 as a base, a a = 0.1 or a = 0.4, which satisfies all of the conditions in the specimen 1, the sample 3, the electromechanical coupling coefficient _{K 33} is located at least 30% , The piezoelectric g ₃₃ constant is 20 × 10 ⁻³ V / N or more, and corresponds to the secondary phase transition in the temperature range of −40 to 150 ° C. as shown in FIGS. 2 , 3 , 4 and 5. It can be seen that the target has been achieved without discontinuities.

  FIG. 8 is a diagram showing the measurement result of the temperature change rate of the relative permittivity of the sample 1. Thus, for example, in sample 1, it was confirmed in FIGS. 1 and 2 that no discontinuous portion corresponding to the second-order phase transition was confirmed in the temperature range of −40 to 150 ° C., but the Curie temperature higher than that was confirmed. As a result of investigating the temperature dependence of the relative permittivity in the behavior up to, as shown in FIG. 8, the discontinuous behavior of the relative permittivity accompanying the second-order phase transition was not 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, the sample 1 has a high Curie temperature, can be subjected to SMD reflow mounting, and can be replaced with a conventional lead-containing piezoelectric element as a piezoelectric element not containing lead.

2 is an X-ray diffraction diagram of Sample 1. FIG. 3 is a graph showing a temperature change rate of a piezoelectric g ₃₃ constant of sample 1. 3 is a graph showing a temperature change rate of a resonance / anti-resonance frequency of a sample 1. 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 resonance / anti-resonance frequency of a sample 3. 4 is a graph showing a temperature change rate of a piezoelectric g ₃₃ constant of a sample 19. 3 is a graph showing a temperature change rate of a resonance / anti-resonance frequency of a sample 19. 4 is a graph showing a measurement result of a temperature change rate of a relative dielectric constant of a sample 1;

Claims (3)

Potassium sodium lithium niobate _{(K x Na y Li 1-} x-y) NbO 3, strontium titanate and SrTiO _3, when the bismuth ferrate and BiFeO _3, and the potassium niobate sodium-lithium , said strontium titanate, and the bismuth _{ferrite, (1-a-b)} (K x Na y Li 1-x-y) NbO 3 + aSrTiO 3 + bBiFeO 3
0 <a ≦ 0.1
0 <b ≦ 0.11
0 ≦ x ≦ 0.18
0.8 ≦ y <1
The piezoelectric ceramic composition which comprises in the range expressed in. 0 . 01 ≤ a ≤ 0.08
0.01 ≦ b ≦ 0.09
0 ≦ x ≦ 0. 075
0.8 ≤ y ≤ 0.98
Der Ru claim 1 piezoelectric ceramic composition. Obtained by firing the claims 1 or 2 piezoelectric ceramic composition according electromechanical coupling factor _{k 33} is 30% or more, and the piezoelectric _{g 33} constant is 20 × ¹⁰ -3 V / N or more der Turkey A piezoelectric ceramic characterized by

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