阅读说明：本技术 压电陶瓷组合物及压电致动器 (Piezoelectric ceramic composition and piezoelectric actuator ) 是由 田畑周平 平山武 志村元 于 2020-03-02 设计创作，主要内容包括：在铌酸钾钠系的压电陶瓷组合物中,发生斜方晶系的晶体结构与正方晶系的晶体结构之间的相转变的转变温度存在于-20℃以上60℃以下的温度区域。将在该温度区域晶体结构为斜方晶系时的线膨胀系数设为αo,将晶体结构为正方晶系时的线膨胀系数设为αt时,αt/αo为0.72以上。(In the potassium-sodium niobate-based piezoelectric ceramic composition, a transition temperature at which a phase transition between an orthorhombic crystal structure and a tetragonal crystal structure occurs exists in a temperature range of-20 ℃ to 60 ℃. When the linear expansion coefficient in the case where the crystal structure is orthorhombic in the temperature region is represented by α o, and the linear expansion coefficient in the case where the crystal structure is tetragonal is represented by α t, α t/α o is 0.72 or more.)

1. A piezoelectric ceramic composition which is a potassium-sodium niobate-based piezoelectric ceramic composition,

a transition temperature at which a phase transition between an orthorhombic crystal structure and a tetragonal crystal structure occurs exists in a temperature region of-20 ℃ to 60 ℃,

when the linear expansion coefficient in the case where the temperature region crystal structure is orthorhombic is represented by α o, and the linear expansion coefficient in the case where the temperature region crystal structure is tetragonal is represented by α t, α t/α o is 0.72 or more.

2. The piezoelectric ceramic composition according to claim 1, wherein α t/α o is greater than 0.85.

3. The piezoelectric ceramic composition according to claim 1 or 2, wherein the piezoelectric ceramic composition is represented by the composition formula A_xBO₃Represents, comprising:

k, Na and Li in an amount of 9 or more based on the amount of the substance occupying the A site;

nb, Ta and Sb in an amount of 9 or more based on the amount of the substance occupying the B site;

ag contained in the A site; and

fe contained in the B site.

4. The piezoelectric ceramic composition according to claim 3,

the piezoelectric ceramic composition has a composition formula

{(K_1-u-vNa_uLi_v)_1-w-αAg_wA1_α}_x{(Nb_1-y-zTa_ySb_z)_1-β-γ-δB1_βB2_γFe_δ}O₃It is shown that,

a1 is Bi, La, Ce, Nd or Sm, or their combination,

b1 is Zn, Mg, Yb, Fe, Cu, Co or Ni, or their combination,

b2 is Sn, Ti, Zr, Hf, Ce, Ge, V, W, Nb, Sb or Ta, or a combination thereof.

5. The piezoelectric ceramic composition according to claim 4, wherein the following inequality is satisfied:

0.500≤u≤0.540、

0.00<v≤0.06、

0.00<w≤0.06、

0.99≤x≤1.02、

0.00<y≤0.12、

0.00<z≤0.10、

0.0000<α≤0.0275、

0.000<β≤0.005、

0.000< gamma.less than or equal to 0.005, and

0.0000<δ≤0.0125。

6. the piezoelectric ceramic composition according to claim 4 or 5,

a1 is Bi in the formula,

alpha/delta is 2.2 to 5.0.

7. The piezoelectric ceramic composition according to claim 1, wherein u/v is 10.1 or more and 11.0 or less.

8. The piezoelectric ceramic composition according to claim 1 of claims 4 to 7, wherein z is 0.01 or more and 0.09 or less,

y/z is 0.7 to 10.0.

9. The piezoelectric ceramic composition according to claim 5, wherein A1 is Bi, B1 is Zn, and B2 is Sn, satisfying the following formula:

0.524≤u≤0.540、

0.05≤v≤0.06、

0.02≤w≤0.06、

0.99≤x≤1.02、

0.04≤y≤0.10、

0.06≤z≤0.08、

0.0045≤α≤0.0125、

0.000≤β≤0.005、

β＝γ、

0.0010≤δ≤0.0100。

10. the piezoelectric ceramic composition according to claim 1 of claims 4 to 8,

b1 is any 1 of Zn, Mg, Fe, Cu, Co and Ni,

b2 is any 1 of Sn, Ti, Zr, Hf, Ge, Nb, Sb and Ta.

11. The piezoelectric ceramic composition according to claim 1 to 10, wherein,

comprises Fe and Bi, and has a high Fe content,

the ratio of the amount of Bi substance divided by the amount of Fe substance is 2.2 to 5.0.

12. A piezoelectric actuator having a potassium-sodium niobate-based piezoelectric ceramic, wherein,

a transition temperature at which the piezoelectric ceramic undergoes phase transition between an orthorhombic crystal structure and a tetragonal crystal structure exists in a temperature region when a voltage is applied to the piezoelectric ceramic,

when the linear expansion coefficient in the case where the temperature region crystal structure is orthorhombic is represented by α o, and the linear expansion coefficient in the case where the temperature region crystal structure is tetragonal is represented by α t, α t/α o is 0.72 or more.

Technical Field

The present invention relates to a piezoelectric ceramic composition and a piezoelectric actuator.

Background

Piezoelectric ceramic compositions used for actuators, sensors, oscillators, filters, and the like are known. Various potassium-sodium niobate-based compositions have been proposed as lead-free piezoelectric ceramic compositions (for example, patent documents 1 and 2).

Documents of the prior art

Patent document

Patent document 1: japanese laid-open patent publication No. 2007-145650

Patent document 2: international publication No. 2014/002285

Disclosure of Invention

A piezoelectric ceramic composition according to one embodiment of the present invention is a potassium-sodium niobate-based piezoelectric ceramic composition, wherein a transition temperature at which a phase transition between an orthorhombic crystal structure and a tetragonal crystal structure occurs is in a temperature range of-20 ℃ to 60 ℃, and α t/α o is 0.72 or more when a linear expansion coefficient when the crystal structure is orthorhombic in the temperature range is α o and a linear expansion coefficient when the crystal structure is tetragonal in the temperature range is α t.

Brief description of the drawings

FIG. 1 is a graph showing the composition and characteristics of samples 1 to 15 of the piezoelectric ceramic composition.

FIG. 2 is a graph showing the composition and characteristics of samples 16 to 30 of the piezoelectric ceramic composition.

FIG. 3 is a graph showing the composition and characteristics of samples 31 to 45 of the piezoelectric ceramic composition.

FIG. 4 is a graph showing the composition and characteristics of samples 46 to 56 of the piezoelectric ceramic composition.

Fig. 5 is a cross-sectional view showing an example of the piezoelectric actuator.

Description of the reference numerals

101. cndot. cndot.ceramic composition, 103. cndot. cndot.ta segregation portion, 105. cndot. cndot.ta segregation portion, 117. cndot. cndot.reference portion, and 15. cndot. cndot.actuator substrate (piezoelectric actuator).

Detailed Description

(composition of piezoelectric ceramic composition)

The piezoelectric ceramic composition of the embodiment is a potassium-sodium niobate-based (KNN-based, alkali niobate-based)System) and does not contain lead (Pb). The KNN-based piezoelectric ceramic composition is represented by the simplified composition formula A_xBO₃And (4) showing. The A site mainly contains K (potassium) and Na (sodium). And predominantly Nb (niobium) at the B site. x (molar ratio) is, for example, approximately 1. Further, the piezoelectric ceramic composition has a perovskite structure.

More specifically, the piezoelectric ceramic composition according to the embodiment is represented by the following composition formula.

{(K_1-u-vNa_uLi_v)_1-w-αAg_wA1_α}_x{(Nb_1-y-zTa_ySb_z)_1-β-γ-δB1_βB2_γFe_δ}O₃(1)

In the above formula (1), A1, B1 and B2 are metal elements. With caution, the description is: li is lithium, Ag is silver, Ta is tantalum, Sb is antimony, and Fe is iron. u, v, w, y, z, α, β, γ, and δ represent molar ratios.

As described above, the molar ratio (x) of the a site to the B site is substantially 1 (for example, 0.95 to 1.05). The ratio of the amounts of K and Na to the amount of the A site substance is large. For example, the molar ratio ((1-v) × (1-w-. alpha.)) of the ratio of K to Na at the A site may be 0.80 or more, 0.85 or more, or 0.90 or more. In addition, the ratio of the amount of Nb to the amount of the B site material is small. For example, the molar ratio of the proportion of Nb in the B site ((1-y-z) × (1-. beta. - γ -. delta.)) may be 0.70 or more, 0.75 or more, or 0.80 or more.

The molar ratio of K to Na (1-u-v: u) is approximately 1: 1. however, the amount of Na may be larger than that of K. That is, the piezoelectric ceramic composition of the embodiment may be Na-rich KNN. For example, u/(1-u-v) may be 1.01 or more, 1.1 or more, or 1.2 or more, or may be 1.5 or less, 1.4 or less, or 1.3 or less, and the above lower limit and upper limit may be combined as appropriate.

The piezoelectric ceramic composition contains Li of the same alkali metal at the a site in addition to K and Na as the alkali metal. That is, the piezoelectric ceramic composition of the embodiment is a potassium sodium lithium niobate-based piezoelectric ceramic composition. The molar ratio of Li to K and Na (from another viewpoint, the ratio of the amount of Li in the amount of the substance at the a site) is small. For example, the molar ratio (v × (1-w- α)) of the proportion of Li in the a site may be 0.1 or less, 0.06 or less, or 0.05 or less. In addition, the ratio of the amount of Li, K, and Na in the amount of the a site substance is large. For example, the molar ratio (1-w- α) of the proportions of Li, K and Na in the A site may be 0.9 or more, 0.95 or more, or 0.98 or more. The piezoelectric ceramic composition contains Li, and thus, for example, piezoelectric characteristics are improved.

The piezoelectric ceramic composition contains, at the B site, Ta of group 5 and Sb of group 15 (original group 5B) in addition to Nb of group 5 of the periodic table. The molar ratio of Ta and Sb to Nb (in another viewpoint, the ratio of the amount of Ta and Sb in the amount of a substance at the a site) is small. For example, the molar ratio ((y + z) × (1-. beta. - γ -. delta.)) of the proportions of Ta and Sb in the B site may be 0.25 or less, 0.20 or less, or 0.16 or less. In addition, the ratio of the amounts of Nb, Ta, and Sb to the amount of the substance at the B site is large. For example, the molar ratio (1-. beta. - γ -. delta.) of the proportions of Nb, Ta and Sb at the B site may be 0.90 or more, 0.97 or more or 0.99 or more. The piezoelectric ceramic composition improves, for example, piezoelectric characteristics by containing Ta and/or Sb.

The piezoelectric ceramic composition contains not only K, Na and Li but also Ag and a1 (optional metal elements) at the a site. As can be understood from the above description of the molar ratio of K, Na and Li, the ratio of the amounts of Ag and a1 to the amount of the a site substance (w and α) is small. For example, in contrast to the above description of the molar ratio of K and the like, the molar ratio (w + α) of the proportion of Ag and a1 in the a site may be 0.10 or less, 0.05 or less, or 0.02 or less. The piezoelectric ceramic composition improves, for example, piezoelectric characteristics by containing Ag or the like at the a site.

The piezoelectric ceramic composition contains B1 (an arbitrary metal element), B2 (an arbitrary metal element), and Fe at the B site in addition to Nb, Ta, and Sb. As can be understood from the above description of the molar ratio of Nb, Ta, and Sb, the amounts of B1, B2, and Fe are small in proportion to the amount of the B site substance. For example, in contrast to the above description of the molar ratio of Nb and the like, the molar ratio (β + γ + δ) of the proportion of B1, B2, and Fe in the B site may be 0.10 or less, 0.03 or less, or 0.01 or less. The piezoelectric ceramic composition improves, for example, piezoelectric characteristics by containing Fe or the like at the B site. In addition, Fe contributes to an increase in insulation resistance value.

A1 may be selected from various metals, and may be only 1 metal element or a combination of a plurality of metal elements. In the examples described later, Bi (bismuth), La (lanthanum), Ce (cerium), Nd (neodymium) and Sm (samarium) are exemplified as a 1. Among the above, Bi is a group 15 (original group 5B) metal. As a1, a metal element of group 5 or group 15 other than Bi may be used. Among the above, La, Ce, Nd and Sm are lanthanoids. As a1, lanthanoid elements other than those described above can also be used.

B1 may be selected from various metals, and may be only 1 metal element or a combination of a plurality of metal elements. In the examples described later, Zn (zinc), Mg (magnesium), Yb (ytterbium), Fe (iron), Cu (copper), Co (cobalt), and Ni (nickel) are exemplified as B1. Among the above, Zn, Fe, Cu, Co and Ni are metal elements of the 4 th cycle, and are transition metals except Zn. As B1, for example, transition metals other than those described above in the 4 th cycle can be used. Among the above, Yb is a lanthanoid. As a1, lanthanoid elements other than Yb can also be used.

B2 may be selected from various metals, and may be only 1 metal element or a combination of a plurality of metal elements. In the examples described later, B2 includes Sn (tin), Ti (titanium), Zr (zirconium), Hf (hafnium), Ce (cerium), Ge (germanium), V (vanadium), W (tungsten), Nb (niobium), Sb (antimony), and Ta (tantalum). Among the above, the elements other than Ce are metal elements of 4 th to 6 th periods and groups 4 to 6, 14 (original group 4B) and 15 (original group 5B). As B2, for example, metal elements (except Pb) other than the above-described metal elements of 4 th to 6 th periods, and groups 4 to 6 and groups 14 to 16 (original groups 4B to 6B) can be used. Among the above, Ce is a lanthanoid. As B2, lanthanoid elements other than Ce can also be used.

The molar ratios (u, v, w, x, y, z, α, β, γ, and δ) can be appropriately set. An example is shown below. U is more than or equal to 0.5 and less than or equal to 0.54, v is more than or equal to 0 and less than or equal to 0.06, w is more than or equal to 0 and less than or equal to 0.06, x is more than or equal to 0.99 and less than or equal to 1.02, y is more than 0 and less than or equal to 0.12, z is more than 0 and less than or equal to 0.1, alpha is more than 0 and less than or equal to 0.0275, beta is more than 0 and less than or equal to 0.005, gamma is more than 0 and less than or equal to 0.005, and delta is more than or equal to 0 and less than or equal to 0.0125.

As indicated above, v, w, y, z, α, β, γ, and δ are greater than 0. If these values are more than 0, addition of more or less of Li, Ag, Ta, Sb, Al, B1, B2 and Fe to potassium sodium niobate ((K, Na) NbO₃) The effect of (1). The other lower limit and upper limit are based on the examples described later. When the molar ratio is within the above range, for example, an effect of improving the piezoelectric characteristics can be obtained.

(method for producing piezoelectric ceramic composition)

The method for producing the piezoelectric ceramic composition of the present embodiment may be the same as the known method for producing a potassium-sodium niobate-based piezoelectric ceramic composition, except for the kind of the specific metal element added to the potassium-sodium niobate and the molar ratio thereof. For example, as follows.

First, a powder of a compound (for example, an oxide) of the metal element contained in formula (1) is prepared. Examples of such a compound include K₂CO₃、Na₂CO₃、Li₂CO₃、Ag₂O、Nb₂O₅、Ta₂O₅、Sb₂O₃、Fe₂O₃、Bi₂O₃、ZnO、SnO、SnO₂、SrCO₃、TiO₂、SrTiO₃And the like.

Next, powders of the above-described respective compounds are measured (for example, weighed) so as to have the composition of formula (1). Next, the metered powders were mixed in alcohol by a ball mill (wet mixing was performed). As the ball mill, for example, ZrO can be used₂A ball. As the alcohol, for example, IPA (isopropyl alcohol) can be used. The mixing time may be, for example, 20 hours to 25 hours.

Next, the mixture is dried and then calcined. The pre-firing may be performed, for example, at a temperature of 900 ℃ to 1100 ℃ for about 3 hours in the air. Next, the calcined material was pulverized by a ball mill. Next, a binder is mixed into the pulverized product, and granulation is performed. As the binder, PVA (polyvinyl alcohol) can be used, for example.

Next, the granulated powder is formed into an arbitrary shape and size. The molding pressure may be, for example, about 200 MPa. Then, the molded body is fired to obtain a piezoelectric ceramic composition. The firing may be performed, for example, in the air at a temperature of 1000 ℃ to 1250 ℃ for about 2 hours. Then, the piezoelectric ceramic composition is polarized by applying a voltage of an appropriate magnitude in an appropriate direction, and can be used in a piezoelectric actuator or the like.

(phase transition and linear expansion coefficient of piezoelectric ceramic composition)

The piezoelectric ceramic composition according to the embodiment is used, for example, in a state where the temperature of the piezoelectric ceramic composition and/or the ambient temperature (ambient temperature) of the piezoelectric ceramic composition are within a predetermined driving temperature range. The driving temperature range differs depending on the apparatus using the piezoelectric ceramic composition, and is, for example, from-20 ℃ to 60 ℃ or less, or from 20 ℃ to 40 ℃ or less.

In this drive temperature range, the value of the linear expansion coefficient of the piezoelectric ceramic composition changes according to a change in temperature. The main reasons for this include: a phase transition occurs between an orthorhombic (orthorhombic) crystal structure (hereinafter, sometimes simply referred to as an orthorhombic crystal) and a tetragonal crystal structure (hereinafter, sometimes simply referred to as a tetragonal crystal). In other words, there can be mentioned: the transition temperature of the orthorhombic crystal and the tetragonal crystal exists in the drive temperature region.

More specifically, the piezoelectric ceramic composition has an orthorhombic crystal structure below the transition temperature and a tetragonal crystal structure above the transition temperature. The linear expansion coefficient of tetragonal crystals (denoted by α t) is smaller than the linear expansion coefficient of orthorhombic crystals (denoted by α o). Therefore, for example, when the temperature of the piezoelectric ceramic composition having an orthorhombic crystal structure rises and exceeds the transition temperature, the crystal structure is changed from an orthorhombic system to a tetragonal system, and the linear expansion coefficient is decreased. Conversely, when the temperature of the piezoelectric ceramic composition having a tetragonal crystal structure is lowered to be lower than the transition temperature, the crystal structure is changed from the tetragonal system to the orthorhombic system, and the linear expansion coefficient is increased.

In the piezoelectric ceramic composition of the present embodiment, the difference between α t and α o is small. For example, α t/α o is 0.72 or more. As a result, the change in the linear expansion coefficient corresponding to the temperature change as described above is reduced. Thus, for example, a piezoelectric actuator using the piezoelectric ceramic composition of the present embodiment operates stably. In theory, α t/α o is smaller than 1.

(examples)

With respect to the piezoelectric ceramic compositions of the embodiments, a plurality of samples having different molar ratios a1, B1, and B2 were actually prepared, and the influence of the composition on the characteristics was examined. Fig. 1 to 4 are graphs showing the results.

In the figure, the column "No." indicates the sample number. Here, the compositions and characteristics are exemplified for 56 samples of samples 1 to 56. Columns "u Na", "v Li", "x A", "w Ag", "yTa", "z Sb", "α", "β", "γ", and "δ" indicate values of u, v, x, w, y, z, α, β, γ, and δ in each sample. Columns "a 1", "B1", and "B2" indicate the types of metal elements of a1, B1, and B2 in each sample. In the columns of "a 1", "B1", and "B2" - "indicates that a metal element to be a1, B1, or B2 is not added, and corresponds to α ═ 0, β ═ 0, or γ ═ 0. The "Fe" column indicates the presence or absence of Fe in each sample, and indicates "Fe" if δ >0, and indicates "-" if δ is 0. Note that, although significant digits of a mole ratio not more than a decimal point are substantially the same among a plurality of samples, for convenience, the last 0 is omitted.

The column "d 31 pC/N" indicates the piezoelectric constant d in each sample₃₁Value of (pC/N). With caution, the description is: d₃₁Means at the same pole when a voltage is applied in the polarization direction of the piezoelectric ceramic compositionAnd the piezoelectric characteristics in the direction orthogonal to the polarization direction. d₃₁The larger the value of (b), the larger the strain generated with respect to the strength of the applied electric field or the larger the charge generated with respect to the applied stress. In this column, "0" indicates that polarization cannot be performed.

The column "α t/α o" indicates a value obtained by dividing the value of the linear expansion coefficient α t by the value of the linear expansion coefficient α o in percentage. As described above, α o is a linear expansion coefficient of the piezoelectric ceramic composition when the crystal structure of the piezoelectric ceramic composition is mainly orthorhombic. α t is a linear expansion coefficient of the piezoelectric ceramic composition when the crystal structure of the piezoelectric ceramic composition is mainly tetragonal. Since the linear expansion coefficient α t is smaller than the linear expansion coefficient α o, the larger the value of α t/α o (closer to 100%), the smaller the difference between α t and α o, and the smaller the change in the linear expansion coefficient due to temperature change.

With respect to the piezoelectric constant d₃₁The piezoelectric ceramic composition after polarization was measured in accordance with the specification (electrical test method for EM-4501A piezoelectric ceramic oscillator) defined by JEITA (general society of Electrical information technology industries Association). More specifically, the measurement is performed by an impedance analyzer using a resonance antiresonance method. Based on the above specification, the temperature of the piezoelectric ceramic composition was measured to be 25. + -. 5 ℃.

When the linear expansion coefficients α t and α o are measured, first, the transition temperature is determined for each sample. The transition temperature is determined by examining the temperature dependence of the resonance frequency in the piezoelectric ceramic composition with an impedance analyzer. Specifically, when the crystal structure of the piezoelectric ceramic composition changes, the resonance frequency also changes, and when the horizontal axis is plotted as temperature and the vertical axis is plotted as resonance frequency, an inflection point appears. The temperature at the inflection point was taken as the transition temperature. By measurement using an X-ray diffraction apparatus, it was confirmed that a diffraction pattern attributed to tetragonal crystals can be obtained in a temperature range higher than the transition temperature, and a diffraction pattern attributed to orthorhombic crystals can be obtained in a temperature range lower than the transition temperature. In the present sample, the transition temperature was approximately 25 ℃.

Next, based on the transition temperatures obtained as described above, a1 st temperature region (orthorhombic temperature region) in which the linear expansion coefficient α o is measured when the crystal structure is orthorhombic and a 2 nd temperature region (tetragonal temperature region) in which the linear expansion coefficient α t is measured when the crystal structure is tetragonal are set. The range of the transition temperature. + -. 10 ℃ is excluded from the 1 st temperature region and the 2 nd temperature region. For example, when the transition temperature is 20 ℃, the 1 st temperature range is 10 ℃ or less, and the 2 nd temperature range is 30 ℃ or more. The lower limit of the 1 st temperature zone is-100 ℃. The upper limit of the 2 nd temperature region is the transition temperature from the tetragonal crystal to other crystal structures (about 250 ℃ in this sample).

Then, in the 1 st temperature region and the 2 nd temperature region, the linear expansion coefficient was measured by Thermo-Mechanical Analysis (Thermo-Mechanical Analysis). Specifically, the sample is heated or cooled while a load is applied to the sample by the probe, and the linear displacement of the probe generated thereby is measured to determine the dimensional change (strain) at each temperature. Then, the linear expansion coefficient was determined based on the value that becomes the slope when plotted with the horizontal axis as the temperature and the vertical axis as the strain.

The samples 1, 9 to 15 and 26 do not contain a part of the elements represented by the formula (1) (do not satisfy the formula (1)), and the other samples 2 to 8, 16 to 25 and 27 to 56 satisfy the formula (1). In the former, samples 9 to 15 do not contain 2 or more elements among the elements represented by formula (1), sample 1 does not contain Fe alone, and sample 26 does not contain Sb alone. In other words, the samples that do not satisfy formula (1) are potassium-sodium niobate-based piezoelectric ceramic compositions having simpler compositions than those of the embodiments.

Samples 1 to 8 and 16 to 56 satisfying formula (1) or containing only 1 of the elements represented by formula (1) have a larger α t/α o value than samples 9 to 15 containing 2 or more of the elements represented by formula (1). The former α t/α o is 72% or more (rounded up to the decimal point). The potassium-sodium niobate-based piezoelectric ceramic composition having α t/α o of 72% or more can be used as the piezoelectric ceramic composition of the embodiment without being limited to formula (1).

A sample having a larger α t/α o value than the above may be regarded as the piezoelectric ceramic composition of the present embodiment. For example, a piezoelectric ceramic composition having α t/α o of more than 72% (rounded up or down to a decimal point) can be extracted. In this case, sample 8 is excluded from the samples having α t/α o of 72% or more. Sample 8 is a sample having a larger molar ratio α and δ than other samples.

For example, a piezoelectric ceramic composition having a value of α t/α o of 85% or more (rounded up to the decimal point) can be regarded as the piezoelectric ceramic composition of the present embodiment. Examples of such piezoelectric ceramic compositions include samples 3 to 5, 17, 18, 20, 22, 23, 26, 29, 31 to 34, 36, 38, 39, 41, 42, 46 to 49, 51, and 54.

Satisfying 2 to 8, 16 to 25 and 27 to 56 of the formula (1) in terms of the piezoelectric constant d₃₁And the ratio α t/α o of the linear expansion coefficients, exhibit higher values than any of samples 1, 9 to 15, and 26 that do not satisfy formula (1). Among the samples not satisfying (1), samples 9 to 15 had piezoelectric constant d₃₁The value of (2) is less than 70(pC/N), and no polarization is observed in samples 9 to 12. On the other hand, in all the samples satisfying the formula (1), 70(pC/N) or more can be secured as the piezoelectric constant d₃₁The value of (c).

As is clear from the above, the piezoelectric characteristics were improved by making the composition of the piezoelectric ceramic composition satisfy formula (1). Further, examples of the ranges of the respective molar ratios can be derived from the minimum value and the maximum value of the respective molar ratios of the samples satisfying the formula (1). For example, 0.5. ltoreq. u.ltoreq.0.54 is derived from samples 16 and 17. From samples 18 and 19, 0.02. ltoreq. v.ltoreq.0.06 was derived. W is 0.02. ltoreq. w.ltoreq.0.06 from samples 20 and 21. From samples 29 and 30, 0.99. ltoreq. x.ltoreq.1.02 was derived. From sample 22 and the plurality of samples, y is 0.02. ltoreq. y.ltoreq.0.1. From sample 28 and the plurality of samples, z is 0.06. ltoreq. z.ltoreq.0.1. From samples 2 and 7, 0.0045. ltoreq. alpha. ltoreq.0.0275 was derived. From the plurality of samples and sample 45, 0.00125. ltoreq. beta. ltoreq. 0.00187 was derived. 0.00063. ltoreq. gamma.ltoreq.0.00125 is derived from sample 45 and a plurality of samples. From samples 2 and 7, 0.001. ltoreq. delta. ltoreq.0.0125 was derived.

The highest piezoelectric constant d can be obtained₃₁Of the values of (1) are samples 4 and 51 (d)₃₁117 pC/N). In addition, the maximum α can be obtainedthe value of t/α o is for samples 4 and 26(α t/α o is 88%). Thus, sample 4 had a piezoelectric constant d₃₁And α t/α o, the highest value can be obtained. Fig. 1 to 4 mainly show the composition and characteristics of the sample after the various molar ratios and the kinds of metal elements are changed with the sample 4 as the center (reference).

Since sample 4 has a piezoelectric constant d₃₁And α t/α o, the highest characteristic, the lower limit or the upper limit of each molar ratio can be derived by adding or subtracting a predetermined error or a deviation tolerance to the molar ratio of the sample 4 (the lower limit or the upper limit described above can be corrected).

For example, in the case where y is 0.02. ltoreq. y.ltoreq.0.1, the value of y in sample 4 is the upper limit value. However, it is understood from the characteristics of samples 22 to 25(y is 0.02 to 0.08) having only y values different from that of sample 4 that even if y slightly exceeds 0.1, the characteristics equal to or more than those of samples 4 and 22 to 25 can be obtained. Therefore, the upper limit value of y may be 0.12 (may be y ≦ 0.12.).

The values of β and γ are 0.00125 in sample 4, and narrow ranges including 0.00125 are shown in other samples satisfying formula (1) (0.00167 ≦ β ≦ 0.0125, 0.00063 ≦ γ ≦ 0.00125). On the other hand, B1 related to β and B2 related to γ cause discontinuity of the perovskite structure at the B site, similarly to Fe related to δ. Therefore, the range of values of β and γ can be set with reference to the value of δ. Here, δ may be a value smaller than half of 0.0025 in sample 4 (sample 2), or may be a value 5 times as large as 0.0025 in sample 4 (sample 7). Therefore, β and γ can be set to a range of 0.00125 half to 5 times or less, or included in a narrower range than δ. For example, it can be 0.001. ltoreq. beta. ltoreq.0.005 and 0.001. ltoreq. gamma. ltoreq.0.005.

Among the samples in which α t/α o was 72% or more, Bi was used as A1 in samples 1 to 8 and 16 to 52 in the same manner as in sample 4. Among these, samples 2 to 7 and 16 to 52 have a larger α t/α o value than samples 1 and 8. Here, sample 1 contains no Fe. The value of α/δ of sample 8 is smaller than those of samples 2 to 7 and 16 to 52, and is about 2.1. The value of Bi/Fe (molar ratio) of sample 8 is smaller than that of samples 2 to 7 and 16 to 52, and is about 2.1, even when the molar ratio (x) of A site is taken into consideration. In samples 2 to 7 and 16 to 52, the maximum value of α/δ and/or Bi/Fe was 3.25 of sample 2.

As described above, for example, a piezoelectric ceramic composition in which A1 is Bi and α/δ and/or Bi/Fe is 2.2 to 5.0 can be used. Examples of such piezoelectric ceramic compositions include samples 2 to 7 and 16 to 52. In addition, a piezoelectric ceramic composition having an α/δ ratio and/or a Bi/Fe ratio of 2.5 to 4.0, or 2.5 to 3.25 may be used. Examples of such piezoelectric ceramic compositions include samples 2 to 5 and 16 to 52.

Samples 4 and 16 to 19 are samples having different values of u and v. The piezoelectric constant d of samples 16, 18 and 19₃₁In comparison with the values of (A), the piezoelectric constants d of samples 4 and 17₃₁The value of (2) is large. The u/v values for these samples are, sample 4: 10.48, sample 16: 10. sample 17: 10.8, sample 18: 26.2, sample 19: about 8.7.

According to the above, for example, the u/v range may be set to a range including the u/v values of samples 4 and 17 and not including the values of samples 16, 18, and 19. Examples of the value of u/v include 10.1 to 26.0, 10.1 to 11.0, or 10.48 to 10.80.

Samples 4 and 22 to 28 are samples having different values of y and z. Among them, the piezoelectric constants d of samples 4 and 24, 25 and 27₃₁Is larger than the piezoelectric constant d of the other samples 22, 23, 26 and 28₃₁The value of (2) is large.

As described above, the range of the values of y and z may be set to include the values of y and z of the former sample and not to include the values of y and z of the latter sample. Specifically, the values of z of samples 4 and 24, 25 and 27 are in the range of 0.01 to 0.09, 0.05 to 0.09, or 0.06 to 0.08. The y/z values of samples 4 and 24, 25 and 27 are in the range of 0.7 to 10, 0.9 to 1.8, or 1.0 to 1.67. Samples 22, 23, 26, and 28 do not satisfy at least one of the above-described z range and y/z range.

The samples 4 and 31 to 52 are samples in which the metal elements used as B1 and B2 are different from each other. Wherein the piezoelectric constants d of the samples 4, 33, 34, 38 to 40, 42, 43 and 46 to 52₃₁The value of (d) is larger than the piezoelectric constant d of the other samples 31, 32, 35 to 37, 41, 44 and 45₃₁The value of (2) is large.

As described above, the metal elements of the former samples can be selected as B1 and B2. Specifically, B1 may be any 1 of Zn, Mg, Fe, Cu, Co and Ni. And/or, B2 can be any 1 of Sn, Ti, Zr, Hf, Ge, Nb, Sb and Ta.

Samples 4 and 22 to 25 are samples in which y values for only Ta are different from each other. As understood from these samples, the piezoelectric constant d can be increased by increasing the value of y₃₁The value of (c). More specifically, when y is changed from 0.02 (sample 22) to 0.04 (sample 23), the piezoelectric constant d is set to be₃₁The value of (b) is 90pC/N or more. Therefore, the piezoelectric ceramic composition can have a composition satisfying 0.04. ltoreq. y.ltoreq.0.1 (or 0.12), for example.

As described above, in the potassium-sodium niobate-based piezoelectric ceramic composition of the present embodiment, the transition temperature at which phase transition between the orthorhombic crystal structure and the tetragonal crystal structure occurs is present in the temperature region of-20 ℃ to 60 ℃. In this temperature range, when the linear expansion coefficient when the crystal structure is orthorhombic is α o and the linear expansion coefficient when the crystal structure is tetragonal is α t, α t/α o is 72% or more (rounding off at the 3 rd position after decimal point).

Therefore, for example, a change in the linear expansion coefficient corresponding to a change in the temperature of the piezoelectric ceramic composition is reduced. As a result, for example, prediction of thermal stress generated in the piezoelectric ceramic composition becomes easy. In addition, for example, α t/α o is small, which means that the linear expansion coefficient decreases during the temperature rise. Therefore, for example, in the case where a piezoelectric ceramic composition and a material having a linear expansion coefficient larger than that of the piezoelectric ceramic composition are fixed to each other, when the temperature rises, the difference in the linear expansion coefficient increases. As a result, the thermal stress applied to the piezoelectric ceramic composition increases rapidly. Further, the possibility that the operation of the device using the piezoelectric ceramic composition is not intended is high. However, according to the piezoelectric ceramic composition of the present embodiment, such expansion of the difference in linear expansion coefficient is reduced. Further, the thermal stress applied to the piezoelectric ceramic composition is reduced, and the operation of the device is stabilized.

In the present embodiment, α t/α o may be greater than 0.85. In this case, the above-described effect is further improved.

In the present embodiment, the piezoelectric ceramic composition has the composition formula A_xBO₃And (4) showing. In addition, the piezoelectric ceramic composition may include: k, Na and Li in an amount of 9 or more based on the amount of the substance occupying the A site; nb, Ta and Sb in an amount of 9 or more based on the amount of the substance occupying the B site; ag contained in the A site; fe contained in the B site.

In this case, for example, as can be understood from comparison of samples 2 to 8, 16 to 25, and 27 to 56 having the above-mentioned composition with other samples not having the above-mentioned composition, α t/α o is made 0.72 or more and is used as the piezoelectric constant d₃₁It is easy to ensure a certain degree of size.

In the present embodiment, the piezoelectric ceramic composition can be represented by the above formula (1). Also, a1 may be Bi, La, Ce, Nd, or Sm, or a combination thereof. B1 may be Zn, Mg, Yb, Fe, Cu, Co or Ni, or a combination thereof. B2 may be Sn, Ti, Zr, Hf, Ce, Ge, V, W, Nb, Sb or Ta, or combinations thereof.

With such a composition, α t/α o is set to 0.72 or more as shown in fig. 1 to 4, for example, and the piezoelectric constant d is set to be₃₁It is easy to ensure a certain degree of size. In addition, for example, the piezoelectric ceramic composition is a potassium sodium lithium niobate system among potassium sodium niobate systems, and thus the piezoelectric characteristics are improved. For example, Ta can improve the piezoelectric characteristics, or Fe can increase the insulation resistance value.

In addition, in the present embodiment, the following inequalities may be satisfied: u is more than or equal to 0.500 and less than or equal to 0.540, v is more than or equal to 0.00 and less than or equal to 0.06, w is more than or equal to 0.00 and less than or equal to 0.06, x is more than or equal to 0.99 and less than or equal to 1.02, y is more than 0.00 and less than or equal to 0.12, z is more than or equal to 0.00 and less than or equal to 0.10, alpha is more than 0.0000 and less than or equal to 0.0275, beta is more than 0.000 and less than or equal to 0.005, gamma is more than or equal to 0.000 and less than or equal to 0.0000 and less than or equal to 0.0125.

When the molar ratios satisfy the above ranges, α t/α o is set to 0.72 or more and the piezoelectric constant d is secured to a certain extent as described with reference to fig. 1 to 4, for example₃₁The value of (c) is easy.

In this embodiment, a1 may be Bi. Further, α/δ may be 2.2 to 5.0. In this case, for example, it is easy to set α t/α o to 0.72 or more.

In the present embodiment, u/v may be 10.1 to 11.0. In this case, for example, the piezoelectric constant d is increased₃₁The value of (c) is easy.

In the present embodiment, z may be 0.01 to 0.09. Further, y/z may be 0.7 to 10.0. In this case, for example, the piezoelectric constant d is increased₃₁The value of (c) is easy.

In the present embodiment, B1 may be any of Zn, Mg, Fe, Cu, Co, and Ni. B2 may be any of Sn, Ti, Zr, Hf, Ge, Nb, Sb, and Ta. In this case, for example, the piezoelectric constant d is increased₃₁The value of (c) is easy.

In particular, when a1 is Bi (bismuth), B1 is Zn (zinc), and B2 is Sn (tin), the following formula can be satisfied: u is more than or equal to 0.524 and less than or equal to 0.540, v is more than or equal to 0.05 and less than or equal to 0.06, w is more than or equal to 0.02 and less than or equal to 0.06, x is more than or equal to 0.99 and less than or equal to 1.02, y is more than or equal to 0.04 and less than or equal to 0.10, z is more than or equal to 0.06 and less than or equal to 0.08, alpha is more than or equal to 0.0045 and less than or equal to 0.0125, beta is more than or equal to 0.000 and less than or equal to 0.005, beta is equal to gamma, and delta is more than or equal to 0.0010 and less than or equal to 0.0100. In the case of satisfying the above formula, the piezoelectric constant d₃₁95(pC/N) and α t/α o of 0.81 or more are secured, and the piezoelectric properties are improved, and the thermal stress applied to the piezoelectric ceramic composition can be reduced, thereby stabilizing the operation of the device.

In addition, a1 may be La (lanthanum), Ce (cerium), Nd (neodymium), or Sm (samarium) instead of Bi (bismuth), and in this case, the above-described effects can also be obtained. In the case where B2 is Sn (tin), B1 is Fe (iron), Cu (copper), or Mg (magnesium) instead of Zn (zinc), and the above-described effects can be obtained. In the case where B1 is Zn (zinc), B2 is Ti (titanium), Zr (zirconium), Hf (hafnium), or Ge (germanium) instead of Sn (tin), and the above-described effects can be obtained. In addition, the above-described effects can be obtained also when B2 is Ti (titanium) and B1 is a combination of Mg (magnesium), Fe (iron), or Cu (copper).

In addition, when a1 is Bi (bismuth), B1 is Co (cobalt), Ni (nickel), or Zn (zinc), and B2 is Nb (niobium), Sb (antimony), or Ta (tantalum), the above-described effects can be obtained when β is substantially 2 times γ.

(application example)

FIG. 5 is a sectional view showing an application example of the piezoelectric ceramic composition. The sectional view shows a part of the inkjet head 11. The lower side of the paper plane (the side of (-D3) in fig. 5) is the side where the recording medium (e.g., paper) is disposed.

The head 11 is, for example, a substantially plate-shaped member, and has a plurality of configurations shown in fig. 5 along a plane orthogonal to the axis D3. The thickness (direction D3) of the head 11 is, for example, 0.5mm to 2 mm. A plurality of discharge holes 3 (only one is shown in fig. 5) for discharging droplets are opened on a discharge surface 2a of the head 11 facing the recording medium. The plurality of discharge holes 3 are two-dimensionally arranged along the discharge surface 2 a.

The head 11 is a piezoelectric head that ejects liquid droplets by applying pressure to the liquid by mechanical strain of a piezoelectric element. The head 11 has a plurality of ejection elements 37 each including an ejection hole 3, and one ejection element 37 is shown in fig. 5. The plurality of ejection elements 37 are two-dimensionally arranged along the ejection surface 2 a.

In another aspect, the head 11 includes: a plate-shaped flow path member 13 in which a flow path through which liquid (ink) flows is formed, and an actuator substrate 15 (an example of a piezoelectric actuator) for applying pressure to the liquid in the flow path member 13. The plurality of ejection elements 37 are constituted by the flow path member 13 and the actuator substrate 15. The ejection surface 2a is constituted by a flow path member 13.

The flow path member 13 includes: a common channel 19, and a plurality of individual channels 17 (1 shown in fig. 5) connected to the common channel 19. Each individual flow passage 17 has the above-described discharge hole 3, and further has a connection flow passage 25, a compression chamber 23, and a partial flow passage 21 in this order from the common flow passage 19 to the discharge hole 3. The pressure chamber 23 is open on a surface of the flow path member 13 opposite to the discharge surface 2 a. The partial flow channel 21 extends from the pressurizing chamber 23 toward the discharge surface 2 a. The discharge port 3 opens at the bottom surface 21a of the partial flow path 21.

The individual channels 17 and the common channel 19 are filled with liquid. By applying pressure to the liquid by changing the volume of the plurality of pressurizing chambers 23, the liquid is sent from the plurality of pressurizing chambers 23 to the plurality of partial flow channels 21, and a plurality of liquid droplets are discharged from the plurality of discharge holes 3. Further, the liquid is supplied from the common channel 19 to the plurality of pressurizing chambers 23 through the plurality of connecting channels 25.

The flow path member 13 is configured by stacking a plurality of plates 27A to 27J (hereinafter, a to J are omitted), for example. A plurality of holes (mainly through holes or recesses) constituting the plurality of individual flow paths 17 and the common flow path 19 are formed in the plate 27. The thickness and the number of stacked plates 27 can be appropriately set according to the shape of the individual channels 17 and the common channel 19. The plurality of plates 27 may be formed of a suitable material. The plurality of plates 27 are formed of, for example, metal or resin. The thickness of the plate 27 is, for example, 10 μm to 300 μm. The linear expansion coefficient of the flow path member 13 is larger than the linear expansion coefficients of the actuator substrate 15 and the piezoelectric ceramic composition, for example.

The actuator substrate 15 is substantially plate-shaped having a width in the range of the plurality of pressurizing chambers 23. The actuator substrate 15 is constituted by a piezoelectric actuator of a so-called unimorph type. The actuator substrate 15 may be a piezoelectric actuator of another type such as a bimorph type. For example, the actuator substrate 15 includes, in order from the flow path member 13 side, a diaphragm 29, a common electrode 31, a piezoelectric layer 33, and an individual electrode 35.

The diaphragm 29, the common electrode 31, and the piezoelectric layer 33 extend over the plurality of pressurizing chambers 23 in a plan view. That is, they are provided in common in the plurality of pressurizing chambers 23. An individual electrode 35 is provided in each pressurizing chamber 23. The individual electrode 35 has: a main body 35a overlapping the pressurizing chamber 23, and an extraction electrode 35b extending from the main body 35 a. The extraction electrode 35b contributes to connection with a signal line not shown.

The piezoelectric layer 33 is made of, for example, the piezoelectric ceramic composition of the present embodiment. The portion of the piezoelectric layer 33 sandwiched between the individual electrode 35 and the common electrode 31 is polarized in the thickness direction. Therefore, for example, when an electric field (voltage) is applied in the polarization direction of the piezoelectric layer 33 via the individual electrode 35 and the common electrode 31, the piezoelectric layer 33 contracts in a direction along the layer. The contraction is restricted by the vibration plate 29. As a result, the actuator substrate 15 is deformed so as to be deflected to project toward the pressurizing chamber 23. Further, the volume of the compression chamber 23 is reduced, and pressure is applied to the liquid in the compression chamber 23. When an electric field (voltage) is applied in a direction opposite to the above direction via the individual electrode 35 and the common electrode 31, the actuator substrate 15 is deformed in a manner of being deflected toward the side opposite to the pressurizing chamber 23.

The thickness, material, and the like of each layer constituting the actuator substrate 15 can be appropriately set. For example, the thicknesses of the vibration plate 29 and the piezoelectric layer 33 may be 10 μm to 40 μm, respectively. The thickness of the common electrode 31 may be 1 μm or more and 3 μm or less. The thickness of the individual electrode 35 may be 0.5 μm or more and 2 μm or less. The material of the vibration plate 29 may be a ceramic material having piezoelectricity or not. The material of the common electrode 31 may be a metal material such as Ag-Pd. The material of the individual electrode 35 may be a metal material such as Au.

The temperature range (driving temperature range) used for the head 11 (actuator substrate 15) may be set as appropriate in consideration of various matters. For example, the driving temperature range of the head 11 is 20 ℃ to 40 ℃. As a matter to be considered when setting the drive temperature region, for example, a correlation between the temperature and the viscosity of the ink is given. The driving temperature region of the ejection head 11 can be determined based on specifications, and/or manuals, for example. Among these pieces of information, the driving temperature range is described in the form of, for example, a temperature range in which the head 11 (and/or the printer) can be used, a temperature range in which normal operation of the head 11 is ensured, or a recommended temperature range, but the driving temperature range is generally the same. In the case where 2 or more temperature regions are shown, the widest temperature region can be used as the driving temperature region in the present embodiment.

As described above, the actuator substrate 15 (an example of a piezoelectric actuator) of the application example has the potassium-sodium niobate-based piezoelectric layer 33 (an example of a piezoelectric ceramic). In the piezoelectric layer 33, a transition temperature at which a phase transition between an orthorhombic crystal structure and a tetragonal crystal structure occurs exists in a drive temperature region (for example, 20 ℃ to 40 ℃) which is a temperature region when a voltage is applied to the piezoelectric layer 33. When the linear expansion coefficient in the case where the crystal structure is orthorhombic in the drive temperature region is represented by α o, and the linear expansion coefficient in the case where the crystal structure is tetragonal in the drive temperature region is represented by α t, α t/α o is 0.72 or more.

In this case, for example, after the temperature of the actuator substrate 15 rises, a decrease in the linear expansion coefficient of the actuator substrate 15 can be suppressed. As a result, the expansion of the difference in linear expansion coefficient between the actuator substrate 15 and the flow path member 13 having a larger linear expansion coefficient than the actuator substrate 15 is reduced. Further, an increase in thermal stress generated in the actuator substrate 15 is reduced. This reduces variations in the ejection characteristics and reduces the possibility of deterioration of the actuator substrate 15.

The technique of the present invention is not limited to the above embodiment, and can be implemented in various ways.

For example, the piezoelectric ceramic composition is not limited to the substance represented by formula (1) or a substance similar to formula (1). In addition to actuators, the piezoelectric ceramic composition can be used for sensors, oscillators, filters, and the like. The actuator is not limited to the actuator used for the inkjet head, and may be used for various machines.