JP2018088524A - Lead-free piezoelectric ceramic composition and piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lead-free pressure porcelain composition and a piezoelectric element having a high piezoelectric constant d33 and an electromechanical coupling coefficient kr. SOLUTION: This is a lead-free pressure electromagnetic composition containing a niobate alkaline perovskite oxide having a piezoelectric property as a main phase and containing Ti, and the molar ratio of Na and K in the main phase (Na / (Na + K)). However, 0.50 ≦ (Na / (Na + K)) ≦ 0.60. The main phase is the bond angle between the B-site atom and the oxygen atom when the plane composed of four oxygen atoms perpendicular to the c-axis of the oxygen octahedron of the perovskite structure is observed along the b-axis direction. OBO is 170.0 to 172.5 degrees. Further, the distance between one oxygen atom and the straight line of the B site atom located in the c-axis direction with respect to the straight line connecting the oxygen atoms on both sides of the B site atom forming the bond angle OB—O. The relationship between the distance between the other oxygen atom and the straight line is (β / α) -1 ≦ 0.05. [Selection diagram] Fig. 3

Description

  The present invention relates to a lead-free piezoelectric ceramic composition and a piezoelectric element. Specifically, the present invention relates to a piezoelectric ceramic composition and a piezoelectric element that are lead-free and have excellent piezoelectric characteristics, and further have, for example, excellent thermal durability.

  Many piezoelectric ceramics (piezoelectric ceramics) that have been mass-produced in the past are made of PZT (lead zirconate titanate) material and contain lead. However, in recent years, the development of lead-free piezoelectric ceramics is desired in order to eliminate the adverse effects of lead on the environment.

As a material of such a lead-free piezoelectric ceramic (hereinafter referred to as “lead-free piezoelectric ceramic composition”), for example, a composition formula ANbO ₃ (A is an alkali metal) such as potassium sodium niobate ((K, Na) NbO ₃ ). ) Has been proposed.

However, the ANbO ₃ -based lead-free piezoelectric ceramic composition itself has a problem that it is poor in sinterability and moisture resistance.
In order to solve such a problem, in Patent Document 1 below, by adding Cu, Li, Ta or the like to the ANbO ₃ -based lead-free piezoelectric ceramic composition, the sinterability is improved, and as a result, the piezoelectric constant d ₃₃ and the electrical properties are increased. A method for improving the mechanical coupling coefficient kr is disclosed.

Moreover, in the following patent document 2, the lead-free piezoelectric ceramic composition (0 ≦ x ≦ 0) represented by the general formula {Li _x (K _1−y Na _y ) _1−x } (Nb _1−z Sb _z ) O ₃ 2. 0 ≦ y ≦ 1.0, 0 ≦ z ≦ 0.2 (except for x = z = 0), relatively good sinterability and piezoelectric properties (ie high piezoelectric constant d ₃₃ and electrical It is disclosed that a mechanical coupling coefficient kr) can be achieved.

JP 2000-313664 A JP 2003-342069 A

However, in the piezoelectric ceramic composition described in Patent Document 1, although the sinterability is improved, the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr are inferior to those of the conventional leaded piezoelectric ceramic composition. It is insufficient for practical use.

On the other hand, although the piezoelectric ceramic composition described in Patent Document 2 exhibits relatively high piezoelectric characteristics, the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr are still inferior to those of the leaded piezoelectric ceramic composition. It is insufficient to replace a piezoelectric ceramic composition.

Therefore, in order to commercialize various devices using the lead-free piezoelectric ceramic composition, the development of lead-free piezoelectric ceramic composition has been desired which has a higher piezoelectric constant d ₃₃ and electromechanical coupling factor kr.
The present invention has been made in view of the above problems, its object is to provide a lead-free piezoelectric ceramic composition and a piezoelectric element having a high piezoelectric constant d ₃₃ and electromechanical coupling factor kr.

(1) A first aspect of the present invention relates to a lead-free piezoelectric ceramic composition containing a Ti-containing alkali niobate-based perovskite oxide having piezoelectric characteristics as a main phase.
In this lead-free piezoelectric ceramic composition, the molar ratio of Na to K (Na / (Na + K)) in the main phase satisfies 0.50 ≦ (Na / (Na + K)) ≦ 0.60. In this main phase, a plane composed of four oxygen atoms positioned perpendicular to the c-axis of the oxygen octahedron composed of oxygen atoms around the B site atom of the perovskite structure was observed along the b-axis direction. At this time, the bond angle O—B—O between the B site atom (B) and the oxygen atom (O) is 170.0 to 172.5 degrees.

  Further, the distance between the oxygen atom on one side of the B site atom located in the c-axis direction and the straight line with respect to the straight line connecting the oxygen atoms on both sides of the B site atom forming the bond angle O—B—O. And the distance between the oxygen atom on the other side of the B site atom located in the c-axis direction and the straight line is (β / α) −1 ≦ 0.05. Here, when the two distance values are the same, one distance is α and the other distance is β. When the two distance values are different, the shorter distance is α and the longer distance is Is β.

  In the first aspect, as shown by the configuration described above, an oxygen octahedron composed of oxygen arranged around a B site atom with respect to a unit cell composed of an A site atom of a perovskite structure, Although deviated along a predetermined direction (so-called c-axis direction), B site atoms are not displaced.

  Further, the pair of oxygens sandwiching the B site atom in the predetermined direction (c-axis direction) is also shifted in the same manner corresponding to the shift of the octahedron, but the shift is slight. Specifically, as described above, the relationship between the distances α and β is ((β / α) −1 ≦ 0.05).

According to such a configuration, the main phase has a crystal structure showing effective values for the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr, and the lead-free piezoelectric ceramic composition has a sufficiently high density. That is, as is clear from experimental examples described later, it is possible to realize a lead-free piezoelectric ceramic composition having excellent piezoelectric constant d ₃₃ and electromechanical coupling factor kr.

The piezoelectric constant d ₃₃ can be, for example, higher than 300 pC / N, and the electromechanical coupling coefficient kr can be, for example, higher than 50%.
Moreover, in this 1st aspect, it has high thermal durability and thermal shock stability by the structure mentioned above, for example. Specifically, even if many temperature changes due to thermal cycling, also, even if the thermal shock is applied, there is an advantage that the piezoelectric characteristics such as a piezoelectric constant d ₃₃ and electromechanical coupling factor kr are hardly degraded.

(2) In the second aspect of the present invention, even if the molar ratio of Na and K in the main phase (Na / (Na + K)) satisfies 0.50 <(Na / (Na + K)) <0.60. Good.
In the configuration of the second aspect, the piezoelectric constant d ₃₃ is set by setting the molar ratio of Na and K to the above range when compared with an alkali niobate-based perovskite oxide composed of the same element. In addition, a lead-free piezoelectric ceramic composition having an excellent electromechanical coupling coefficient kr and a higher Curie point Tc can be realized.

(3) In the third aspect of the present invention, even if the molar ratio of Na and K in the main phase (Na / (Na + K)) satisfies 0.52 ≦ (Na / (Na + K)) ≦ 0.56. Good.
In the configuration of the third aspect, when compared with an alkali niobate-based perovskite oxide configured using the same element, the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr are excellent, and a higher Curie point Tc is obtained. The lead-free piezoelectric ceramic composition can be stably realized.

(4) In the fourth aspect of the present invention, the lead-free piezoelectric ceramic composition of any of the first to third aspects may contain Fe and Mg.
In the fourth aspect, the lead-free piezoelectric ceramic composition, by containing Fe and Mg, is possible to realize a lead-free piezoelectric ceramic composition having excellent piezoelectric characteristics including a piezoelectric constant d ₃₃ and electromechanical coupling factor kr it can.

(5) In the fifth aspect of the present invention, the lead-free piezoelectric ceramic composition of any one of the first to third aspects may contain Ni.
In the fifth aspect, the lead-free piezoelectric ceramic composition, by containing Ni, it is possible to realize a lead-free piezoelectric ceramic composition having excellent piezoelectric characteristics including a piezoelectric constant d ₃₃ and electromechanical coupling factor kr.

  (6) According to a sixth aspect of the present invention, there is provided a piezoelectric element comprising: a piezoelectric ceramic composed of the lead-free piezoelectric ceramic composition according to any one of the first to fifth aspects; and an electrode attached to the piezoelectric ceramic. it can.

It is explanatory drawing which shows typically one crystal structure of the lead-free piezoelectric ceramic composition of embodiment. (A) is explanatory drawing which shows the state which looked at the state where the oxygen octahedron has not shifted | deviated in the unit cell along the b-axis direction, (b) is the oxygen octahedron in the unit cell of this embodiment shifted in the c-axis direction. It is explanatory drawing which shows the state which looked at the state which looked along the b-axis direction. It is a perspective view which shows a piezoelectric element. It is a flowchart which shows the manufacture procedure of a piezoelectric element. It is a graph which shows the relationship between Na / (Na + K) and angle (theta). It is a graph which shows the relationship between Na / (Na + K) and (((beta) / (alpha))-1). Na / and (Na + K) is a graph showing the relationship between the piezoelectric constant _{d 33.} It is a graph which shows the relationship between Na / (Na + K) and the electromechanical coupling coefficient kr.

Below, the form for implementing this invention is demonstrated.
[1. Embodiment]
[1-1. Configuration of main parts of lead-free piezoelectric ceramic composition]
First, the characteristic part of the lead-free piezoelectric ceramic composition of the present embodiment will be described.

  The lead-free piezoelectric ceramic composition of the present embodiment is a lead-free piezoelectric ceramic composition containing, as a main phase, an alkali niobate-based perovskite oxide having piezoelectric characteristics and containing Ti and Fe and Mg.

  In this lead-free piezoelectric ceramic composition, the molar ratio of Na to K (Na / (Na + K)) in the main phase satisfies 0.50 ≦ (Na / (Na + K)) ≦ 0.60. The molar ratio is preferably 0.50 <(Na / (Na + K)) <0.60, and more preferably the molar ratio (Na / (Na + K)) is 0.52 ≦ (Na / (Na + K)) ) ≦ 0.56.

  This main phase has a plane composed of four oxygen atoms positioned perpendicular to the c-axis of the oxygen octahedron composed of oxygen atoms around the B site atom of the perovskite structure in the unit cell of the perovskite structure. When observed along the axial direction, the bond angle O—B—O between the B site atom (B) and the oxygen atom (O) is 170.0 to 172.5 degrees.

  Further, with respect to a straight line connecting the oxygen atoms on both sides of the B site atom forming the bond angle O—B—O, the oxygen atom on one side of the B site atom located in the c-axis direction and the straight line And the distance between the oxygen atom on the other side of the B site atom located in the c-axis direction and the straight line satisfies (β / α) −1 ≦ 0.05. Here, when the two distance values are the same, one distance is α and the other distance is β. When the two distance values are different, the shorter distance is α and the longer distance is Is β.

Hereinafter, the structure of the main phase of this lead-free piezoelectric ceramic composition will be described in detail.
As shown in FIG. 1, the main phase of the lead-free piezoelectric ceramic composition has a perovskite structure, basically has a tetragonal unit cell, and each vertex (A site) of the tetragonal crystal has, for example, K (potassium) or A-site metal such as Na (sodium) (A-site atom indicated by A in FIG. 1) is arranged, and B-site metal such as Nb (niobium), for example, in the body center B-site (in FIG. 1) B site atoms indicated by B) are arranged.

Further, since O (oxygen) is arranged in the vicinity of the center (face center) of each tetragonal plane centering on the B site atom, a metal-O _{6 made of} NbO ₆ or the like is formed inside the unit cell. It has a structure in which octahedrons are arranged. Hereinafter, an octahedron composed of an oxygen portion is referred to as an oxygen octahedron (O ₆ octahedron).

In particular, in the present embodiment, as shown in FIG. 1, the O ₆ octahedron is slightly shifted in the c-axis direction with respect to the unit cell composed of A-site atoms.
Specifically, for example, as shown in FIG. 2A, in the structure in which the O ₆ octahedron is not displaced, when viewed along the a-axis direction (the same applies when viewed along the b-axis direction), The unit cell is a square, and each oxygen atom is located at the midpoint of a square diagonal formed by A-site atoms. In FIGS. 2A and 2B, oxygen atoms before the B site atom and beyond the B site atom are omitted.

On the other hand, in the present embodiment, as shown in FIG. 1, the O ₆ octahedron is slightly shifted in the c-axis direction (for example, the upper side of FIG. 1), so as shown in FIG. When viewed along the b-axis direction, all the oxygen atoms around the B-site atom are also basically displaced in the c-axis direction (for example, upward in FIG. 2B) by a predetermined distance (ΔH).

FIG. 2B shows only four oxygen atoms on the upper, lower, left and right sides of the figure among the oxygen atoms adjacent to the B site atom.
Therefore, when viewed along the b-axis direction, in the a-axis direction, the oxygen atom O ₂₁ on the left side of the figure from the center B site atom and the oxygen atom O ₂₂ on the right side of the figure from the B site atom are Are arranged so as to be bent at the B-site atom (B-site metal). Therefore, the bond angle θ (that is, the angle O ₂₁ −B—O ₂₂ ) between the oxygen atom O ₂₁ , the B site atom, and the oxygen atom O ₂₂ is not 180 °, but is in the range of 170.0 to 172.5 degrees. Has a bond angle.

Similarly, when viewed along the b-axis direction, the first line L1 that is a straight line connecting the left and right oxygen atoms O ₂₁ , O ₂₂ and one of FIG. 2B (here, adjacent to the B site atom). the distance between the oxygen atoms O ₁₁ above), the distance and, the relationship between the oxygen atom O ₁₂ of the first line L1 and the other (here the lower adjacent to the B-site atom) is, (beta /Α)-1≦0.05. Here, when the two distance values are the same, one distance is α and the other distance is β. When the two distance values are different, the shorter distance is α and the longer distance is Is β.

In FIG. 2 (b), the distance between the first line L1 and the oxygen atoms O ₁₂ is, for than the distance between the first line L1 and the oxygen atoms O ₁₁ is large, the distance of the former β, the latter distance is α. In the following, “(β / α) −1” indicating the relationship between the two distances is also simply referred to as “deviation ((β / α) −1)”.

In other words, the first line L1 connecting the left and right oxygen atom _{O 21, O 22,} and the first line L1 to the left and right oxygen atom _{O 11, O 12} present in the upper and lower (c-axis) direction with respect to the first line the second line L2 (i.e., straight line extending in the c-axis direction through the B-site atom in perpendicular to the first line L1) connecting the distance between the intersections of the C, and one oxygen atom O ₁₁ and the intersection point C And the relationship of the distance between the other oxygen atom O ₁₂ and the intersection C is (β / α) −1 ≦ 0.05.

This means that in this embodiment, the O ₆ octahedron composed of oxygen atoms arranged around the B site atom is in the c-axis direction with respect to the unit cell composed of the A site atom of the perovskite structure. This shows that the B site atoms are not displaced. At the same time, also an oxygen atom across the B-site atom in the c-axis direction, corresponding to the total displacement of the O ₆ octahedra, so are shifted substantially in the same manner, there are no distortions in the O ₆ octahedra, Or even if there is distortion, it shows very little.
[1-2. Overall structure of lead-free piezoelectric ceramic composition]
Next, the entire configuration of the lead-free piezoelectric ceramic composition, such as materials constituting the main phase and subphase of the lead-free piezoelectric ceramic composition, will be described in detail.

  The lead-free piezoelectric ceramic composition in the present embodiment includes at least a main phase (first crystal phase) made of an alkali niobate-based perovskite oxide having piezoelectric characteristics, and a subphase (second crystal) that is a crystal phase other than the main phase. Phase, etc.).

The subphase is to stabilize the structure of the main phase by mixing with the main phase, to improve the piezoelectric constant d ₃₃ and electromechanical coupling factor kr. The subphase may include a crystal phase (such as a third crystal phase) other than the second crystal phase. This will be specifically described below.
<Preferred main phase composition>
In the present embodiment, the perovskite oxide that forms the main phase is an alkali niobate-based perovskite oxide.

  The alkaline component of the alkali niobate perovskite oxide contains at least an alkali metal (K (potassium), Na (sodium), Li (lithium), Rb (rubidium), etc.), and an alkaline earth metal (Ca ( Calcium), Sr (strontium), Ba (barium) and the like. As such an niobate-based perovskite oxide, those represented by the following composition formula (1) are preferable.

(K _a Na _b Li _C C _d ) _e (D _f E _g ) O _h (1)
Here, the element C is one or more of Ca (calcium), Sr (strontium), Ba (barium), and Rb (rubidium), and the element D is at least one of Nb (niobium), Ti (titanium), and Zr (zirconium). One or more elements including Nb or Ta, element E is Mg (magnesium), Al (aluminum), Sc (scandium), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Zn (zinc) , Ga (gallium), Y (yttrium), a + b + c + d = 1, e is arbitrary, f + g = 1, and h are arbitrary values constituting the perovskite.

  In the composition formula (1), when the elements C and E can each contain one or two kinds of elements and the element D can contain one to three kinds of elements, the following composition formula (1a) Can be rewritten.

(K _a Na _b Li _c C1 _d1 C2 _d2 ) _e (D1 _f1 D2 _f2 D3 _f3 E1 _g1 E2 _g2 ) O _h (1a)
Here, a + b + c + d1 + d2 = 1, e is arbitrary, f1 + f2 + f3 + g1 + g2 = 1, and h is an arbitrary value constituting the perovskite. The composition formula (1a) is equivalent to the composition formula (1). As can be understood from this example, when the element C includes two types of metal elements, the value of the coefficient d of the element C is represented by the sum of the coefficients d1 and d2 of the two types of elements C1 and C2. The same applies to the elements D and E.

  In the composition formula (1), K (potassium), Na (sodium), Li (lithium), and the element C (Ca, Sr, Ba, Rb) are arranged at a so-called A site having a perovskite structure. Element D (one or more of Nb, Ti, Zr including at least Nb) and element E (one or more of Mg, Al, Sc, Mn, Fe, Co, Ni, Zn, Ga, Y) are included. It is arranged at the so-called B site. Of the coefficients a, b, c, and d of the element at the A site, the sum (a + b + c) of the first three coefficients is preferably not 0, but the coefficient d may be zero. Of the coefficients f and g of the elements D and E at the B site, the coefficient f of the element D is preferably not 0, but the coefficient g of the element E may be zero.

  That is, the alkali niobate-based perovskite oxide of this embodiment includes at least one alkali metal (K, Na, Li, Rb) at the A site and contains an alkaline earth metal (Ca, Sr, Ba). In addition, the B site contains at least one of Nb, Ti, and Zr containing at least Nb and other metals (Mg, Al, Sc, Mn, Fe, Co, Ni, Zn, A perovskite oxide that may contain one or more of Ga, Y) is preferred.

Particularly, among the A site atoms of the main phase, those in which Na (sodium) and K (potassium) occupy 89 mol% or more are preferable in that they are excellent in terms of the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr. Further, as a constituent element of the B site, one containing Nb is most preferable. An niobate-based perovskite oxide containing Nb is preferred in that it can provide a lead-free piezoelectric ceramic composition having a higher Curie temperature (Tc) than an alkali tantalate-based perovskite oxide containing no Nb. This can be inferred from the results of FIG. 6 of International Publication No. 2011/093021 disclosed by the present applicant.

As the values of the coefficients a, b, c, d, e, f, g, h in the composition formula (1), the piezoelectric constant d ₃₃ of the lead-free piezoelectric ceramic composition among the combinations of values that establish the perovskite structure. A preferable value can be selected from the viewpoint of the electromechanical coupling coefficient kr.

  Specifically, the coefficients a, b, and c are values of 0 or more and less than 1, respectively, and a = b = c = 0 (that is, a piezoelectric ceramic composition that does not include K, Na, and Li) is established. Preferably not. The coefficients a and b of K and Na are typically 0 <a ≦ 0.6 and 0 <b ≦ 0.6. The coefficient c of Li may be zero, but 0 <c ≦ 0.2 is preferable, and 0 <c ≦ 0.1 is more preferable. The coefficient d of the element C (one or more of Ca, Sr, Ba) may be zero, but 0 <d ≦ 0.2 is preferable, and 0 <d ≦ 0.1 is more preferable.

The coefficient e for the entire A site is arbitrary, but preferably 0.80 ≦ e ≦ 1.10, more preferably 0.84 ≦ e ≦ 1.08, and most preferably 0.88 ≦ e ≦ 1.07. .
The coefficient h of oxygen can take any value such that the main phase constitutes a perovskite oxide. A typical value for the coefficient h is about 3, with 2.9 ≦ h ≦ 3.1 being preferred. The value of the coefficient h can be calculated from the electrical neutral condition of the main phase composition. However, as the composition of the main phase, a composition slightly deviating from the electrical neutral condition is acceptable.

A typical composition of the main phase is (K, Na, Li, Ca, Ba) _e (Nb, Zr) O _h , and contains K, Na, and Nb as main metal components. Since this main phase has K, Na, and Nb as main metal components, the material composed of the main phase is also referred to as “KNN” or “KNN material”, and the main phase is also referred to as “KNN phase”. If the main phase is formed of the KNN phase, a lead-free piezoelectric ceramic composition having excellent piezoelectric characteristics can be provided.
<Preferred subphase composition>
Moreover, the lead-free piezoelectric ceramic composition may contain a metal oxide different from the main phase as a subphase. The subphase preferably contains, for example, one or more metal oxides selected from the following (a) to (e).

(A) Mg (magnesium), Ni (nickel), Co (cobalt), Fe (iron), Mn (manganese), Cr (chromium), Zr (zirconium), Ti (titanium), Ag (silver), Zn ( Zinc), Sc (Scandium), Bi (Bismuth) A single metal oxide composed of a metal element (b) M-Ti-O-based spinel compound (element M is a 1-5 valent metal)
(C) A ₂ B ₆ O _13- based compound (element A is a monovalent metal, element B is a 2-6 valent metal)
(D) A ₃ B ₅ O _15- based compound (element A is a 1 to 2 valent metal, element B is a 2 to 5 valent metal)
(E) A-Ti-B-O compound (element A is an alkali metal, element B is at least one of Nb and Ta)
The subphase containing these compounds does not have piezoelectric characteristics by itself, but has a function of improving sinterability and denseness by being mixed with the main phase. Further, the addition of these sub-phases, it is possible to obtain a lead-free piezoelectric ceramic composition having excellent piezoelectric constant d ₃₃ and electromechanical coupling factor kr. The total content of the subphases is preferably 5% by volume or less, more preferably 2% by volume or less, based on the entire lead-free piezoelectric ceramic composition. When the sum of the content of the subphase is more than 5% by volume, there is a possibility that the piezoelectric constant d ₃₃ and electromechanical coupling factor kr is rather deteriorated.

Examples of the single metal oxide include MgO, NiO, Co ₃ O ₄ , Fe ₂ O ₃ , MnO ₂ , Cr ₂ O ₃ , ZrO ₂ , TiO ₂ , Ag ₂ O, ZnO, Sc ₂ O ₃ , Bi. ₂ O ₃ can be used. Of these, it is particularly preferable to use one, two, or three of Co ₃ O ₄ , ZnO, and Fe ₂ O ₃ as subphases because the structure of the main phase can be stabilized.

The composition of the M-Ti-O-based spinel compound can be represented by the following formula (2).
M _x TiO _y (2)
Here, the element M is a 1-5 pentavalent metal element, and Li (lithium), Na (sodium), K (potassium), Mg (magnesium), Al (aluminum), Sc (scandium), Cr (chromium). ), Mn (manganese), Fe (iron), Co (cobalt), Ni (nickel), Zn (zinc), Ga (gallium), Y (yttrium), Zr (zirconium), Sn (tin), Sb (antimony) ), Nb (niobium), Ta (tantalum), Si (silicon), and Hf (hafnium).

  In addition, when Li is contained as the element M, in order to form a spinel compound, it is preferable that 1 or more types of metal elements other than Li of the said metal elements are contained with Li.

  The coefficients x and y are relative values when the Ti content is 1. In order to form the spinel compound, the coefficient x preferably satisfies 0.5 ≦ x ≦ 8.0, and more preferably satisfies 0.5 ≦ x ≦ 5.0. The coefficient y is an arbitrary value that forms a spinel compound, but typically it is preferable to satisfy 2.0 ≦ y ≦ 8.0.

Specific spinel compounds include, for example, NiFeTiO ₄ , MgFeTiO ₄ , Ni ₂ (Ti, Zr) O ₄ , Ni ₂ (Ti, Hf) O ₄ , Ni _1.5 FeTi _0.5 O ₄ , CoMgTiO ₄ , It is preferable to use CoFeTiO ₄ , (Fe, Zn, Co) ₂ TiO ₄ , or CoZnTiO ₄ . Spinel compounds, the structure of the main phase so stabilized, it is possible to obtain a lead-free piezoelectric ceramic composition having excellent piezoelectric constant d ₃₃ and electromechanical coupling factor kr.

  The spinel compound may be a normal spinel compound or a reverse spinel compound. Whether or not the compound is a spinel compound can be determined by performing Rietveld analysis using a powder X-ray diffraction (XRD) diffraction result.

As the A ₂ B ₆ O _13- based compound, the element A (monovalent metal) is at least one of Li, Na, and K, and the element B (2-6 hexavalent metal) is Co, Fe, Mg, Ni. , Zr, Mn, Al, Nb, Ta, and W can be used. Specifically, for example, K ₂ (Ti, Nb, Mg) ₆ O ₁₃ , K ₂ (Ti, Nb, Co, Zn) ₆ O ₁₃ or the like can be used.

As the A ₃ B ₅ O _15- based compound, the element A (1 to 2 valent metal) is at least one of Ba, Ca, Sr, Na, K, and Li, and the element B (2 to 5 valent metal) is used. A compound in which at least one of Nb, Mn, Fe, Ni, Co, Zn, and Zr is used can be used.

Specifically, for example, (Ba, Na, K) ₃ (Nb, Ni, Fe) ₅ O ₁₅ , (Ba, Na, K) ₃ (Nb, Co, Ni) ₅ O ₁₅ , (Ba, Na, K) ₃ (Nb, Zn) ₅ O ₁₅ , (Ba, Na, K) ₃ (Nb, Mn) ₅ O ₁₅ , (Ba, Na, K) ₃ (Nb, Fe, Zn, Co) ₅ O ₁₅ etc. Can be used.

As the A-Ti-B-O-based compound, those having the composition of the following formula (3) or (4) can be used.
A _1-x Ti _1-x B _{1 + x} O ₅ (3)
A ₁ Ti ₃ B ₁ O ₉ (4)
Here, the element A is at least one of alkali metals (K (potassium), Rb (rubidium), Cs (cesium), etc.), and the element B is Nb (niobium). The coefficient x in the above equation (3) is an arbitrary value. However, the coefficient x preferably satisfies 0 ≦ x ≦ 0.15. When the coefficient x takes a value within this range, the structure of the compound is stabilized and a uniform crystal phase can be obtained.

Specific compounds according to the above formula (3) include KTiNbO ₅ , K _0.90 Ti _0.90 Nb _1.10 O ₅ , K _0.85 Ti _0.85 Nb _1.15 O ₅ , RbTiNbO _5. , Rb _0.90 Ti _0.90 Nb _1.10 O ₅ , Rb _0.85 Ti _0.85 Nb _1.15 O ₅ , CsTiNbO ₅ , Cs _0.90 Ti _0.90 Nb _1.10 O ₅ etc. It can be used.

From the viewpoint of the structural stability of this compound, the coefficient x preferably satisfies 0 ≦ x ≦ 0.15 when the element A is K (potassium) or Rb (rubidium). In the case of Cs (cesium), it is preferable to satisfy 0 ≦ x ≦ 0.10. Select K (potassium) as the element A, by selecting the Nb (niobium) as the element B, can be obtained unleaded piezoelectric ceramic composition having excellent piezoelectric constant d ₃₃ and electromechanical coupling factor kr.

The crystal phases represented by the above formulas (3) and (4) are both complex oxidations of element A (alkali metal), Ti (titanium), and element B (at least one of Nb and Ta). It is common in that it is a thing. Thus, the complex oxide of element A, Ti (titanium), and element B is referred to as “A-Ti—B—O-based complex oxide”. An A-Ti-B-O-based composite oxide (element A is an alkali metal, element B is Nb, and the contents of elements A, B, and Ti are all zero) can be used.
[1-2. Piezoelectric element]
Next, the piezoelectric element of this embodiment will be described.

  As shown in FIG. 3, the piezoelectric element 1 has electrodes 5 and 7 disposed on the upper and lower surfaces, which are the main surfaces of the disk-shaped piezoelectric ceramic 3 made of the lead-free piezoelectric ceramic composition (ie, sintered body). It has the structure which was made.

In addition, as the piezoelectric element 1, it is possible to form the piezoelectric elements 1 having various other shapes and configurations.
[1-3. Method for manufacturing piezoelectric element]
Next, a method for manufacturing the piezoelectric element 1 will be described based on the flowchart of FIG.

As shown in FIG. 4, in step T110, as a raw material for the main phase (KNN phase), K ₂ CO ₃ powder, Na ₂ CO ₃ powder, Li ₂ CO ₃ powder, Rb ₂ CO ₃ powder, CaCO ₃ powder, SrCO ₃ powder, BaCO ₃ powder, Nb ₂ O ₅ powder, TiO ₂ powder, ZrO ₂ powder, MgO powder, Al ₂ O ₃ powder, Sc ₂ O ₃ powder, MnO ₂ powder, Fe ₂ O ₃ powder, Co ₃ O ₄ Necessary ones are selected from the raw materials such as powder, NiO powder, ZnO powder, Ga ₂ O ₃ powder, Y ₂ O ₃ powder, and the coefficient a in the composition formula of the main phase as shown in Table 1 described later, for example. , B, c, d, e, f, g.

Then, ethanol is added to these raw material powders, and wet mixing is preferably performed for 15 hours or more in a ball mill to obtain a slurry.
In step T120, the mixed powder obtained by drying the slurry is calcined at, for example, 600 ° C. to 1100 ° C. for 1 to 10 hours in an air atmosphere to generate main phase calcined powder.

  In step T130, as shown in Table 1 below, each of the main phase calcined powders is weighed with an oxide powder as a secondary phase, and a ball mill is used to add a dispersant, a binder, and ethanol, and pulverize and mix the slurry. And Moreover, the mixed powder obtained by drying this slurry is calcined at, for example, 600 ° C. to 1100 ° C. for 1 to 10 hours in an air atmosphere to produce calcined powder.

  In step T140, the calcined powder obtained in step T130 is again added with a dispersant, a binder and ethanol, and pulverized and mixed to form a slurry. The slurry is dried by a spray dryer and granulated, for example, at a pressure of 20 MPa. A uniaxial press is performed to form a desired shape. In addition, the shape of the typical piezoelectric ceramic suitable for the various apparatuses as this embodiment is a disk shape, a column shape, a rectangular flat plate shape, or the like. Then, for example, a CIP process (cold isostatic pressing process) is performed at a pressure of 150 MPa to obtain a molded body.

In process T150, the obtained molded object is hold | maintained at 500 degreeC-800 degreeC, for example in an atmospheric condition for 2 to 10 hours, and the degreasing process which degreases a binder is performed.
In step T160, the molded body obtained after the degreasing step is fired by holding for 2 to 50 hours at a specific temperature (for example, 1150 ° C.) selected from, for example, 1000 ° C. to 1300 ° C. in an air atmosphere. A piezoelectric ceramic 3 is obtained.

  The firing in step T160 is preferably sealed firing performed in a state where the molded body is sealed in a sealed container. The reason for this is to prevent metal elements such as alkali metals (Li, Na, K) contained in the compact from disappearing to the outside during firing. As such a sealed container, for example, Alumina Saya A-1174 manufactured by Otakese Serum Co., Ltd. can be used.

  In step T170, the piezoelectric ceramic 3 is processed according to the dimensional accuracy required for the piezoelectric element 1. In step T180, the electrodes 5 and 7 are attached to the piezoelectric ceramic 3 thus obtained, and polarization is performed in step T190.

Thereby, the piezoelectric element 1 of this embodiment is obtained.
[1-4. effect]
The lead-free piezoelectric ceramic composition of the present embodiment is composed of an alkali niobate perovskite oxide having piezoelectric characteristics as a main phase and containing Ti, and a molar ratio of Na and K in the main phase (Na / (Na + K )) Satisfies 0.50 ≦ (Na / (Na + K)) ≦ 0.60. The molar ratio is preferably 0.50 <(Na / (Na + K)) <0.60, and more preferably 0.52 ≦ (Na / (Na + K)) ≦ 0.56.

  In this main phase, a plane composed of four oxygen atoms positioned perpendicular to the c-axis of the oxygen octahedron composed of oxygen atoms around the B site atom of the perovskite structure was observed along the b-axis direction. In this case, the bond angle O—B—O between the B site atom and the oxygen atom is 170.0 to 172.5 degrees.

  Further, the distance between the oxygen atom on one side of the B site atom located in the c-axis direction and the straight line with respect to the straight line connecting the oxygen atoms on both sides of the B site atom forming the bond angle O—B—O. And the distance between the oxygen atom on the other side of the B site atom located in the c-axis direction and the straight line is (β / α) −1 ≦ 0.05.

According to such a configuration, the main phase has a crystal structure showing effective values for the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr, and the lead-free piezoelectric ceramic composition has a sufficiently high density (for example, The water absorption of the lead-free piezoelectric ceramic composition (sintered body) is 0.1% or less).

Therefore, the lead-free piezoelectric ceramic composition of the present embodiment has a remarkable effect that the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr are excellent.
Therefore, the piezoelectric element 1 using the piezoelectric ceramic 3 made of the lead-free piezoelectric ceramic composition having the above-described configuration has excellent piezoelectric characteristics (that is, a high piezoelectric constant d ₃₃ and an electromechanical coupling coefficient kr).

Moreover, the lead-free piezoelectric ceramic composition of the present embodiment has, for example, high thermal durability and thermal shock stability due to the above-described configuration. Specifically, even if many temperature changes due to thermal cycling, also, even if the thermal shock is applied, there is an advantage that the piezoelectric characteristics such as a piezoelectric constant d ₃₃ and electromechanical coupling factor kr are hardly degraded.

Moreover, the lead-free piezoelectric ceramic composition and the piezoelectric element 1 of the present embodiment can be widely used for vibration detection applications, pressure detection applications, oscillation applications, piezoelectric device applications, and the like.
For example, sensors (such as knock sensor and combustion pressure sensor) that detect various vibrations, actuators, high voltage generators, various drive devices, position control devices, vibration suppression devices, fluid discharge devices (paint discharge, fuel discharge, etc.), etc. It can be used for various devices. In addition, the piezoelectric ceramic composition and the piezoelectric element 1 according to the embodiment are particularly suitable for applications requiring excellent thermal durability (for example, a knock sensor and a combustion pressure sensor).

[2. Experimental example]
Next, experimental examples conducted for confirming the effects of the present invention will be described.
[2-1. Experimental Example 1]
This Experimental Example 1 is an experimental example for confirming the effects of the above-described configuration of the present invention, that is, excellent effects regarding the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr.

In Experimental Example 1, Tables 1 and 2 below show materials and the like of a plurality of sample compositions including examples within the scope of the present invention. Table 3 below and FIGS. 5 to 8 show the molar ratio (Na / (Na + K)) and the bond angle θ (angle O—B—O) for a plurality of sample compositions including examples within the scope of the present invention. ) And the deviation ((β / α) −1) show the experimental results regarding the influence on the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr. 5 to 8, only the samples S01 to S09 are shown.

  In Table 1, with respect to the samples S04 to S08 and S11 to S16 of the examples and the samples S01 to S03, S09, S101, S10, and S17 of the comparative examples, the components of the main phase and the subphase at the time of mixing the materials, The ratio (Na / (Na + K)) is also shown, and the subphase ratio (volume%) in the piezoelectric ceramic composition at the time of mixing the materials is also shown.

  Elements C to E and coefficients a to g of the main phase are for the above formula (1a). As shown in Tables 1 and 2, the composition of the main phase (coefficient of each element) is slightly different for each sample. Further, the values of the coefficients a to g in the composition of the main phase are values at the time of mixing the powder raw material in step T110 in FIG.

In Tables 1 and 2, the sample numbers with (*) mean that these are comparative examples.
The sintered body of each sample was prepared according to steps T110 to T160 of FIG. 4 described above. In addition, the shape after shaping | molding in process T140 was made into disk shape (diameter 20mm, thickness 2mm). With respect to the sintered body of each sample thus obtained, the bond angle θ and the deviation ((β / α) -1) were determined as follows.

Moreover, about the sintered compact of the said sample, dry weight W1 and saturation weight W2 were measured according to JIS-R-1634, and the water absorption was computed using the following formula.
Water absorption rate (%) = {(W2-W1) / W1} × 100
This water absorption is an index indicating the denseness of the sintered body. A sintered body having a low density has a high water absorption rate because the sintered body includes a large number of pores. On the other hand, a sintered body with high density has a low water absorption rate because there are few pores in the sintered body.

<Measurement of angle θ>
First, an XRD sample was prepared. The XRD sample was prepared by pulverizing to a primary particle size of about 10 μm by a dry method using a SiN mortar and enclosing it in a Lindeman glass capillary having an inner diameter of 0.2 mmφ.

  For XRD measurement, the beam line (BL5S1) of Aichi Synchrotron Light Center was used, and the X-ray wavelength was set to 0.7 mm. The crystal structure of the main phase KNN was determined by fitting the XRD pattern and the calculation pattern under the 2θ range of 5 ° to 70 ° using the RIETAN-2000 code. The unit cell of the main phase KNN was 1 × 1 × 1 corresponding to the simple perovskite lattice, and the space group was assumed to be P4 mm (99). At this time, each axis was defined to have a relationship of a-axis = b-axis <c-axis.

In the analysis of atomic coordinates, the B site atom (Nb) is fixed, and the z coordinate (the same direction as the c-axis direction) of the A site atom (K or Na) and the oxygen atom (O ₁ , O ₂ ) is used as a variable parameter. . At this time, O ₁ is an oxygen atom arranged in the c-axis direction with respect to the B site atom, and O ₂ is an oxygen atom arranged on the ab plane with respect to the B site atom.

And angle (theta) (namely, bond angle) was calculated | required from the coordinate value of the computed main phase KNN.
Specifically, the coordinates of each atom of the O ₂ —B site atom —O ₂ forming the bond angle were determined, and the bond angle θ shown in Table 3 below was determined from these coordinates.

<Measurement of deviation ((β / α) -1)>
Further, the deviation ((β / α) -1) was obtained from the coordinate value of the main phase KNN calculated as described above. That is, the arrangement asymmetry of O ₁ and O ₂ with respect to the z axis was confirmed. The method for calculating the deviation ((β / α) -1) is as described above.

Separately from this, the samples S01 to S17 and S101 were processed in steps T170 to T190 in FIG.
Then, by using a piezoelectric element corresponding to each sample, according to a known method, as the characteristics of the piezoelectric ceramic, the relative dielectric constant ε ₃₃ ^T / ε ₀ , the dielectric loss tan δ, the piezoelectric constant d ₃₃ , the electromechanical coupling coefficient kr, The mechanical coupling coefficient kt, mechanical quality Qm, and Curie temperature Tc were measured.

Among these, the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr were obtained by JEITA EM-4501.
The results obtained by the above-described experiment are shown in the following Table 3 and FIGS. 5 to 8, only the samples S01 to S09 are shown.

As is apparent from Table 3 and FIGS. 5 and 6, the samples S04 to S08 and S11 to S16 of the examples within the scope of the present invention have a Na / (Na + K) molar ratio, a bond angle θ, a deviation ((β / Since α) -1) is within the scope of the present invention, the piezoelectric constant d ₃₃ is higher than 300 [pC / N], the electromechanical coupling coefficient kr is higher than 55.0 [%], and excellent piezoelectric characteristics. This is preferable.

In particular, when 0.50 <Na / (Na + K) <0.56, the samples S05 to S07 are more piezoelectric than the samples S04 and S08 when compared with the main phase KNN configured using the same element. The constant d ₃₃ and the electromechanical coupling coefficient kr are excellent, and a higher Curie point Tc is preferable. It was confirmed that this tendency was applied when viewed between the samples S11 to S15 of the examples configured using the same elements and the comparative examples S10 and S17. Further, when 0.52 ≦ Na / (Na + K) ≦ 0.56, the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr are excellent when compared with the main phase KNN configured using the same element, In addition, it is preferable from the viewpoint of stably obtaining a sample having a higher Curie point Tc.

Further, as shown in Table 3 and FIGS. 7 and 8, the samples S04 to S08 and S11 to S16 of this example have a relative dielectric constant ε ₃₃ ^{T in} addition to the piezoelectric constant d ₃₃ and the electromechanical coupling coefficient kr. / Ε ₀ , dielectric loss tan δ, electromechanical coupling coefficient Kt, mechanical quality Qm, and Curie point Tc are also preferable because they have piezoelectric characteristics suitable for use as a piezoelectric element.

On the other hand, in the samples S01 to S03, S09, S101, S10, and S17 of comparative examples outside the scope of the present invention, any one of the piezoelectric characteristics is inferior to the above example, which is not preferable.
[2-2. Experimental Example 2]
This Experimental Example 2 is an experimental example in which the thermal durability of the lead-free piezoelectric ceramic composition was examined.

  Specifically, a thermal pressure cooker test was performed on each sample as an endurance test under the following conditions. And it dried for half a day with the dryer (65 degreeC), and measured the electromechanical coupling coefficient kr at room temperature after that. The results are shown in Table 4 below.

In this test, samples S03, S05, S101, and S14 were used as evaluation targets.
<Conditions>
Temperature: 121 ° C
Humidity: 95%
Dew point: 119.9 ° C
Time: 24h, 48h, 72h

  As is apparent from Table 4, the samples S05 and S14 of the examples of the present invention have an electromechanical engagement coefficient kr that is unchanged from the initial stage even after 72 hours of endurance, and is excellent in thermal durability. It was suitable.

On the other hand, the samples S03 and S101 of the comparative example are not preferable because the electromechanical engagement coefficient kr decreases with time.
Note that the present invention is not limited to the embodiments and examples, and it goes without saying that the present invention can be implemented in various modes without departing from the present invention.

1 Piezoelectric element 3 Piezoelectric ceramic 5 Electrode 7 Electrode

Claims (6)

A lead-free piezoelectric ceramic composition containing, as a main phase, an alkali niobate-based perovskite oxide having piezoelectric characteristics and containing Ti,
The molar ratio (Na / (Na + K)) of Na (sodium) to K (potassium) in the main phase satisfies 0.50 ≦ (Na / (Na + K)) ≦ 0.60,
The main phase was observed along the b-axis direction as a plane composed of four oxygen atoms positioned perpendicular to the c-axis of the oxygen octahedron composed of oxygen atoms around the B site atoms of the perovskite structure. When the bond angle O—B—O between the B site atom (B) and the oxygen atom (O) is 170.0 to 172.5 degrees,
In addition, with respect to a straight line connecting the oxygen atoms on both sides of the B site atom forming the bond angle O—B—O, the oxygen atom on one side of the B site atom located in the c-axis direction and the straight line And the distance between the oxygen atom on the other side of the B site atom located in the c-axis direction and the straight line is (β / α) −1 ≦ 0.05 (provided that When the two distance values are the same, one distance is α and the other distance is β, and when the two distance values are different, the shorter distance is α and the longer distance is Is a lead-free piezoelectric ceramic composition.   The molar ratio (Na / (Na + K)) of Na (sodium) to K (potassium) in the main phase satisfies 0.50 <(Na / (Na + K)) <0.60. The lead-free piezoelectric ceramic composition according to 1.   The molar ratio (Na / (Na + K)) of Na (sodium) to K (potassium) in the main phase satisfies 0.52 ≦ (Na / (Na + K)) ≦ 0.56. 2. A lead-free piezoelectric ceramic composition according to 2.   The lead-free piezoelectric ceramic composition according to any one of claims 1 to 3, further comprising Fe (iron) and Mg (magnesium).   Furthermore, Ni (nickel) is contained, The lead-free piezoelectric ceramic composition of any one of Claims 1-3 characterized by the above-mentioned.   A piezoelectric element comprising: a piezoelectric ceramic composed of the lead-free piezoelectric ceramic composition according to any one of claims 1 to 5; and an electrode attached to the piezoelectric ceramic.