JP2021005583A - Piezoelectric ceramic - Google Patents

Abstract

To provide a novel piezoelectric ceramic with an excellent piezoelectric characteristic (especially, a piezoelectric d31 constant) without containing lead.SOLUTION: A piezoelectric ceramic has a perovskite crystal structure and is formed by one having a component expressed by a composition formula: {(K1-yNay)1-zLiz}(Nb1-vTav)O3-(x/2)Bi2O3 (where, 0.0001≤x≤0.0040, 0.40<y<0.55, 0.01≤z≤0.10, 0.01≤v≤0.40, 0.04≤z+v/9≤0.06). When optimizing the composition, a piezoelectric charge sensor output d31 constant of the piezoelectric ceramic is 100 pm/V or more, and a dielectric loss tanδ is 2.2% or less. Such a piezoelectric ceramic is suitable for an infrastructure vibration sensor.SELECTED DRAWING: Figure 2

Description

The present invention relates to piezoelectric ceramics, and more particularly to novel piezoelectric ceramics made of lead-free perovskite-type oxides.

Piezoelectric ceramics refer to ceramics that exhibit a piezoelectric effect. As the piezoelectric ceramics, such as barium titanate (BaTiO _3), lead titanate (PbTiO _3), lead zirconate titanate (Pb (Ti, Zr) O 3, PZT) and the like are known. All of these are ferroelectrics having a perovskite-type crystal structure.
Of these, PZT is known as a material exhibiting the highest piezoelectric effect among piezoelectric ceramics. However, although lead-containing piezoelectric ceramics such as PZT exhibit high piezoelectric characteristics, they have a drawback of having a large load on the environment. Therefore, various proposals have been made conventionally for piezoelectric ceramics that exhibit high piezoelectric characteristics and do not contain lead.

For example, Patent Document 1, the general _{formula: {Li y (Na 1-} x K x) 1-y} a (Nb 1-zw Ta z Sb w) O 3 ( where, 1 <a ≦ 1.1, Perovskite-type oxide represented by 0.30 ≦ x ≦ 0.70, 0.02 ≦ y ≦ 0.10, 0.0 ≦ z ≦ 0.5, 0.01 ≦ w ≦ 0.1) A piezoelectric / electrostrictor composition obtained by adding and mixing a fixed amount of Bi ₂ O ₃ and / or Mn O ₂ and sintering the mixture is disclosed.
The document describes that such a method can be used to obtain a piezoelectric / electrostrained porcelain composition having a large electric field-induced strain when a high electric field is applied.

In Patent Document 2,
_{(A) 100 {Li 0.03 (} Na 0.55 K 0.45) 0.97} 1.010 (Nb 0.918 Ta 0.082) O 3 piezoelectric / electrostrictive porcelain composition having a composition represented by -0.03BiO _1.5, and,
_{(B) 100 {Li 0.06 (} Na 0.55 K 0.45) 0.94} 1.010 (Nb 0.918 Ta 0.082) O 3 -0.10MnO piezoelectric / electrostrictive porcelain composition having a composition represented by ₂ -0.03BiO _1.5 is disclosed Has been done.
It is described in the same document that the former piezoelectric d ₃₁ constant is 70 pm / V and the latter piezoelectric d ₃₁ constant is 93 pm / V.

Piezoelectric materials are used for various purposes, one of which is an infrastructure vibration sensor. "Infrastructure vibration sensor" refers to a sensor for diagnosing the soundness of a structure by measuring the vibration, displacement, etc. of a structure such as a road, a bridge, a plant, or a tunnel. Infrastructure vibration sensors are required not only to accurately diagnose the soundness of structures, but also to have high reliability that enables long-term diagnosis in a real environment. Therefore, in addition to high piezoelectric characteristics, piezoelectric materials for infrastructure vibration sensors are required to have high strength, high Curie temperature, high water resistance (moisture resistance), and long-term stability of material characteristics.

However, the conventional piezoelectric material containing lead has high piezoelectric characteristics but a large environmental load. In addition, the process cost is high because a sintering temperature of 1100 ° C. or higher is required.
On the other hand, Patent Document 1 describes a composition in which Ta, Sb, Mn, and Bi are further added to an alkaline niobate-based perovskite-type oxide. However, although the document describes the electric field-induced strain of such a composition, it does not describe the piezoelectric d ₃₁ constant.
Further, Patent Document 2 discloses a composition in which Ta and Bi are further added to an alkaline niobate-based perovskite-type oxide, and a composition in which Mn is further added in addition to these. However, all the compositions described in Patent Document 2 have a low piezoelectric d ₃₁ constant.

JP-A-2010-030818 JP-A-2009-256182

An object to be solved by the present invention is to provide a novel piezoelectric ceramic which does not contain lead and has excellent piezoelectric characteristics (particularly, piezoelectric d ₃₁ constant).
Another problem to be solved by the present invention is to provide a novel piezoelectric ceramic suitable as an infrastructure vibration sensor.

In order to solve the above problems, the piezoelectric ceramics according to the present invention have a perovskite type crystal structure and have a composition represented by the following formula (1).
_{{(K 1-y Na y} ) 1-z Li z} (Nb 1-v Ta v) O 3 - (x / 2) Bi 2 O 3 ... (1)
However,
0.0001 ≤ x ≤ 0.0040,
0.40 <y <0.55,
0.01 ≤ z ≤ 0.10.
0.01 ≤ v ≤ 0.40,
0.04 ≤ z + v / 9 ≤ 0.06.

Conventional niobate-alkali perovskite-type oxides have a low piezoelectric d ₃₁ constant, and the values are all less than 100 pm / V.
On the other hand, if Ta and Bi are added to the niobate alkaline perovskite type oxide and the addition amount of each element is optimized, the piezoelectric characteristics are excellent even without adding Sb and / or Mn. Piezoelectric ceramics can be obtained. When the composition is optimized, the piezoelectric d ₃₁ constant becomes 100 pm / V or more. It is considered that this is because the sintering density is improved by adding Bi. Further, it is considered that Bi is replaced with A site in a trivalent state, so that the electron distribution of the crystal lattice is changed and the amount of permanent polarization is increased.

It is a figure which shows the Bi quantity dependence of the piezoelectric d ₃₁ constant. It is a figure which shows the Bi quantity dependence of the piezoelectric d ₃₁ constant (enlarged view of FIG. 1). It is a figure which shows the Bi quantity dependence of a relative permittivity ε ₃₃ ^T / ε ₀ . It is a figure which shows the Bi amount dependence of the dielectric loss tan δ. It is a figure which shows the Bi quantity dependence of the piezoelectric g ₃₁ constant. It is a figure which shows the Bi quantity dependence of the electromechanical coupling coefficient K _p . It is a figure which shows the Bi quantity dependence of the electromechanical coupling coefficient K ₃₁ .

It is a figure which shows the Bi amount dependence of Young's modulus Y ₁₁ ^E. It is a figure which shows the Li amount and Ta amount dependence of a piezoelectric d ₃₁ constant. It is a figure which shows the Li amount and Ta amount dependence of a crystal phase and a morphotropic phase boundary (MPB). It is a figure which shows the Li amount and Ta amount dependence of the Curie temperature and the morphotropic phase boundary (MPB). It is a comparison of the amount of Ta and the amount of Li of the present invention and the prior art.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Piezoelectric ceramics]
The piezoelectric ceramic according to the present invention has a perovskite-type crystal structure and has a composition represented by the following formula (1).
_{{(K 1-y Na y} ) 1-z Li z} (Nb 1-v Ta v) O 3 - (x / 2) Bi 2 O 3 ... (1)
However,
0.0001 ≤ x ≤ 0.0040,
0.40 <y <0.55,
0.01 ≤ z ≤ 0.10.
0.01 ≤ v ≤ 0.40,
0.04 ≤ z + v / 9 ≤ 0.06.

[1.1. composition]
[1.1.1. x]
Wherein (1), x represents the ratio of (K, Na, Li) ( Nb, Ta) O 3 and _{Bi 2 O 3 / Bi 2 O} 3/2 of the number of moles second to the total number of moles. If x becomes too small, the amount of Bi that is substituted and solid-solved in the crystal lattice decreases. As a result, the change in the charge distribution in the lattice becomes small, and the piezoelectric characteristics deteriorate. In addition, the sintering density also decreases. Therefore, x needs to be 0.0001 or more. x is preferably 0.0005 or more, more preferably 0.0010 or more.

On the other hand, if x becomes too large, Bi ₂ O ₃ which is a non-piezoelectric material is precipitated at the grain boundary, and the piezoelectric characteristics are sharply lowered. Therefore, x needs to be 0.0040 or less. x is preferably 0.0035 or less, more preferably 0.0030 or less.

[1.1.2. y]
In the formula (1), y represents the ratio of the number of moles of Na to the total number of moles of K and Na contained in (K, Na, Li) (Nb, Ta) O ₃ . If y becomes too small, the distance from the phase boundary of the crystal phase (orthorhombic (Ortho) -tetragonal (Tetra)) becomes long on the phase diagram, and the lattice flexibility due to the phase boundary becomes small. As a result, the piezoelectric characteristics deteriorate. Therefore, y needs to be greater than 0.40. y is preferably 0.43 or more, more preferably 0.45 or more.

On the other hand, if y becomes too large, it becomes far from the phase boundary and the piezoelectric characteristics deteriorate. Therefore, y needs to be less than 0.55. y is preferably 0.53 or less, more preferably 0.52 or less.

[1.1.3. z]
In formula (1), z represents the ratio of the number of moles of Li to the total number of moles of K, Na, and Li contained in (K, Na, Li) (Nb, Ta) O ₃ . If z becomes too small, the piezoelectric characteristics deteriorate. Therefore, z needs to be 0.01 or more. z is preferably 0.02 or more, more preferably 0.03 or more.

On the other hand, if z becomes too large, Li precipitates as a different phase such as Li ₂ CO ₃ , and the piezoelectric characteristics deteriorate. Therefore, z needs to be 0.10 or less. z is preferably 0.08 or less, more preferably 0.06 or less.

[1.1.4. v]
In the formula (1), v represents the ratio of the number of moles of Ta to the total number of moles of Nb and Ta contained in (K, Na, Li) (Nb, Ta) O ₃ . If v becomes too small, the piezoelectric characteristics deteriorate. Therefore, v needs to be 0.01 or more. v is preferably 0.02 or more, more preferably 0.04 or more.

On the other hand, if v becomes too large, the Curie temperature drops to 200 ° C. or lower, and the characteristics deteriorate during long-term use. Therefore, v needs to be 0.40 or less. v is preferably 0.35 or less, more preferably 0.30 or less.

[1.1.5. Component balance (z + v / 9)]
The piezoelectric ceramics according to the present invention have a boundary (morphotropic phase boundary, MPB) in which the crystal structure changes from orthorhombic to tetragonal. MPB mainly depends on the amount of Li (z) and the amount of Ta (v) (see FIG. 10). The piezoelectric characteristics of the piezoelectric ceramics are highest when the composition is on the MPB line, and the distance from the MPB line decreases the piezoelectric characteristics.
When the MPB line of the piezoelectric ceramic according to the present invention is approximated by a straight line, the slope of the straight line is about -1/9. Further, "z + v / 9" is a measure indicating the magnitude of the deviation from the MPB line. In order to obtain high piezoelectric characteristics, z + v / 9 needs to be 0.04 or more and 0.06 or less. z + v / 9 is preferably 0.043 or more and 0.057 or less, and more preferably 0.046 or more and 0.054 or less.

[1.2. Characteristic]
[1.2.1. Piezoelectric charge sensor output d ₃₁ constant]
The "piezoelectric charge sensor output d ₃₁ constant (hereinafter, also simply referred to as" piezoelectric d ₃₁ constant ")" is polarized in the thickness direction (three-axis direction) of a thin rectangular plate and in the long side direction (one-axis direction). A constant that represents the magnitude of strain that occurs when a unit electric field is applied while the stress level is zero when vibrating.
In general, the larger the piezoelectric d ₃₁ constant, the larger the output and the higher the sensitivity when the output circuit of the sensor is a charge detection circuit. When the composition of the piezoelectric ceramics according to the present invention is optimized, the piezoelectric d ₃₁ constant becomes 100 pm / V or more. When the composition is further optimized, the piezoelectric d ₃₁ constant becomes 110 pm / V or more, or 120 pm / V or more.

[1.2.2. Dielectric loss]
“Dielectric loss tan δ” means a numerical value indicating the degree of electrical energy loss in a capacitor. In general, the smaller the dielectric loss tan δ, the less electrodes are wasted. When the composition of the piezoelectric ceramics according to the present invention is optimized, the dielectric loss tan δ is 2.2% or less. When the composition is further optimized, the dielectric loss tan δ is 2.0% or less, or 1.5% or less.

[1.3. Use]
The piezoelectric ceramic according to the present invention is
(A) Lead-free,
(B) The Curie temperature is higher than that of the conventional PZT, and it can be used up to a high temperature.
(C) High strength,
(D) Low temperature sintering at a temperature of about 1000 ° C. is possible.
There are advantages such as.
Therefore, the piezoelectric ceramics according to the present invention are, for example,
(A) Piezoelectric material for infrastructure vibration sensor,
(B) Piezoelectric materials for abnormal vibration detection sensors installed in various devices (air conditioners, heaters, etc.) in buildings, factories, etc.
It is suitable for such as.

[2. Piezoelectric ceramics manufacturing method]
The piezoelectric ceramic according to the present invention is
(A) The raw materials are mixed so as to have a predetermined composition, and the raw materials are mixed.
(B) The raw material mixture is calcined under predetermined conditions and then calcined.
(C) After appropriately crushing the calcined powder, the calcined powder is molded and sintered.
(D) It can be produced by polarization-treating the sintered body.
The production conditions are not particularly limited, and it is preferable to select the optimum conditions according to the desired composition.

[3. Action]
Conventional niobate-alkali perovskite-type oxides have a low piezoelectric d ₃₁ constant, and the values are all less than 100 pm / V.
On the other hand, if Ta and Bi are added to the niobate alkaline perovskite type oxide and the addition amount of each element is optimized, the piezoelectric characteristics are excellent even without adding Sb and / or Mn. Piezoelectric ceramics can be obtained. When the composition is optimized, the piezoelectric d ₃₁ constant becomes 100 pm / V or more. It is considered that this is because the sintering density is improved by adding Bi. Further, it is considered that Bi is replaced with A site in a trivalent state, so that the electron distribution of the crystal lattice is changed and the amount of permanent polarization is increased.

Piezoelectric materials used in infrastructure vibration sensors include
(A) The noise is small (that is, the dielectric loss (tan δ) is low and the mechanical quality coefficient Q _m (= the reciprocal of the elastic loss) is high).
(B) High sensitivity (that is, large piezoelectric d ₃₁ constant and electromechanical coupling coefficient K ₃₁ ).
(C) The usable temperature is high,
(D) High strength (ie, Young's modulus),
Etc. are required.
Since the piezoelectric ceramics according to the present invention satisfy these conditions, they are suitable as piezoelectric materials used for infrastructure vibration sensors.

(Examples 1 and 2, Comparative Examples 1 and 5)
[1. Preparation of sample]
The sample was synthesized by a conventional solid phase reaction method. As a raw material, an oxide or carbonate of a commercially available reagent was used. The raw materials were mixed so as to be {(K _0.5 Na _0.5 ) _0.97 Li _0.03 } (Nb _0.8 Ta _0.2 ) O _3- x (Bi ₂ O ₃ ) / 2. x is 0% (Comparative Example 1), 0.1% (Example 1), 0.3% (Example 2), 0.5% (Comparative Example 2), 1.0% (Comparative Example 3). , 2.0% (Comparative Example 4), or 5.0% (Comparative Example 5). The obtained mixed powder was calcined in the air at 600 ° C. for 5 hours.
Next, the obtained calcined powder was crushed and then molded into a predetermined shape. Further, the molded product was sintered in the air at 1150 to 1175 ° C. for 1 hour.

[2. Test method]
From the obtained sintered body, a disk-shaped sample having a diameter of 11 mm × a thickness of 0.5 mm and a rectangular sample having a diameter of 15 mm × 4 mm × 0.5 mm were cut out. Au sputter-deposited electrodes were attached to the upper and lower surfaces of the sample, and polarization treatment was performed at 100 ° C. for 10 minutes under the condition of 2 to 5 kV / mm. Further, for the polarized sample, the impedance analyzer HP4194A manufactured by Azilent Technology Co., Ltd. was used, and the resonance antiresonance method (Japan Electronics and Information Technology Industries Association standard, JEITA EM-4501A, "Electrical test method of piezoelectric ceramic oscillator (" The piezoelectric characteristics were evaluated according to 1993.3., Revised 2015.10.) ”).

[3. result]
[3.1. Bi amount dependence of various characteristics]
The results are shown in Tables 1 and 2. Further, FIGS. 1 and 2 show the Bi amount dependence of the piezoelectric d ₃₁ constant. FIG. 3 shows the Bi quantity dependence of the relative permittivity ε ₃₃ ^T / ε ₀ . FIG. 4 shows the Bi amount dependence of the dielectric loss tan δ. FIG. 5 shows the Bi amount dependence of the piezoelectric g ₃₁ constant. FIG. 6 shows the Bi amount dependence of the electromechanical coupling coefficient K _p . FIG. 7 shows the Bi amount dependence of the electromechanical coupling coefficient K ₃₁ . Further, FIG. 8 shows the Bi amount dependence of Young's modulus Y ₁₁ ^E. The following can be seen from Tables 1 to 2 and FIGS. 1 to 8.

(1) When a small amount of Bi is added to (K, Na, Li) (Nb, Ta) O ₃ , the piezoelectric d ₃₁ constant can be improved without impairing the sinterability. However, when the amount of Bi added was 0.5% or more, the piezoelectric d ₃₁ constant decreased sharply (see FIG. 2). Therefore, the amount of Bi added is preferably 0.4% or less.
(2) The dielectric loss tan δ does not depend much on the amount of Bi added. When the amount of Bi added was 0.5% or less, tan δ was 2.2% or less.

(3) By adding a small amount of Bi to (K, Na, Li) (Nb, Ta) O ₃ , the relative permittivity ε ₃₃ ^T / ε ₀ can be improved without impairing the sinterability. .. However, when the amount of Bi added was 0.5% or more, the relative permittivity ε ₃₃ ^T / ε ₀ was lower than that of Comparative Example 1 in which Bi was not added.
(4) The piezoelectric g ₃₁ constant, the electromechanical coupling coefficient K _p , and the electromechanical coupling coefficient K ₃₁ all decreased as the amount of Bi added increased.
(5) Young's modulus Y ₁₁ ^E increased as the amount of Bi added increased.

[3.2. La amount and Ta amount dependence of various characteristics]
FIG. 9 shows the dependence of the piezoelectric d ₃₁ constant on the amount of Li and the amount of Ta. From FIG. 9, the following can be seen.
(1) The closer to MPB (Morphotropic Phase Boundary, Tetra-Ortho phase boundary), the larger the piezoelectric d ₃₁ constant. This is because the closer to the phase boundary, the smaller the energy difference between the two crystal phases, and the easier it is for crystal transformation with respect to mechanical stress and applied voltage.
(2) The optimum composition region is Li: 0.01 to 0.04 and Ta: 0.1 to 0.3. The composition is preferably within ± 0.005 from the MPB line.

FIG. 10 shows the dependence of the crystal phase and the morphotropic phase boundary (MPB) on the amount of Li and the amount of Ta. From FIG. 10, the following can be seen.
(1) In MPB, the crystal phase changes from tetragonal (Tetra) to orthorhombic (Ortho) or from orthorhombic to orthorhombic. As a result, the piezoelectric constant increases on the MPB line. The desirable composition of the present invention is within ± 0.005 from the MPB line.
(2) When the amount of Li exceeds 0.10, a different phase of the non-piezoelectric phase appears, so that the piezoelectric constant decreases. Therefore, this composition range should not be used.

FIG. 11 shows the dependence of the Curie temperature and the morphotropic phase boundary (MPB) on the amount of Li and the amount of Ta. From FIG. 11, the following can be seen.
(1) The Curie temperature is preferably 200 ° C. or higher for characteristic stability during long-term use. The Curie temperature is preferably 250 ° C. or higher, more preferably 300 ° C. or higher.
(2) However, it is necessary that the piezoelectric constant satisfies a high condition (that is, both the Curie temperature and the piezoelectric characteristics are compatible).

FIG. 12 shows a comparison between the amount of Ta and the amount of Li of the present invention and the prior art. From FIG. 12, the following can be seen.
(1) In the embodiment of the present invention, the Curie temperature is 300 ° C. or higher, the piezoelectric d ₃₁ constant is 100 pm / V or higher, and the above conditions are satisfied at the same time.
(2) Further, the characteristics can be improved by adding the optimum amount of Bi.

Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention.

The piezoelectric ceramics according to the present invention can be used as a piezoelectric material used for an infrastructure vibration sensor, a piezoelectric material used for an abnormal vibration detection sensor installed in various devices (air conditioners, heaters, etc.) in buildings, factories, etc. ..

Claims (4)

Piezoelectric ceramics having a perovskite-type crystal structure and a composition represented by the following formula (1).
_{{(K 1-y Na y} ) 1-z Li z} (Nb 1-v Ta v) O 3 - (x / 2) Bi 2 O 3 ... (1)
However,
0.0001 ≤ x ≤ 0.0040,
0.40 <y <0.55,
0.01 ≤ z ≤ 0.10.
0.01 ≤ v ≤ 0.40,
0.04 ≤ z + v / 9 ≤ 0.06. The piezoelectric ceramic according to claim 1, wherein the piezoelectric charge sensor output d ₃₁ constant is 100 pm / V or more. The piezoelectric ceramic according to claim 1 or 2, wherein the dielectric loss tan δ is 2.2% or less. The piezoelectric ceramic according to any one of claims 1 to 3, which is used for an infrastructure vibration sensor.

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