JP3062210B2 - Piezoelectric strain material - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric electrostrictive material for an actuator that can be used for positioning in a precision machine tool, a flow control valve, a brake device of an automobile, and the like.

[Problems to be solved by conventional technology and invention]

Substances that have the property of causing mechanical strain when an electric field is applied are generally called piezoelectric materials or piezoelectric electrostrictive materials, and as electromechanical transducers, bimorphs, piezoelectric ignition elements, ultrasonic vibrators, piezoelectric buzzers, ceramic filters Widely used for etc.

In general, when an electric field is applied to a piezoelectric material, its crystal structure changes, and the crystal transformation point exhibits a maximum amount of strain (electromechanical coupling constant). Since the crystal transformation point is different for each piezoelectric material, an appropriate piezoelectric material is selected and used according to the target operating temperature.

Such piezoelectric materials include BaTiO ₃ , Pb (Zr, Ti) O
₃ (PZT), LiNbO ₃ , LiTaO _{3 and the} like are known. Further, a material obtained by adding other oxides or the like to the above-described materials to improve various characteristics of the piezoelectric material is also used.

By the way, PZT, which is widely used as a piezoelectric material,
Although it has a strain amount of about 1.5 × 10 ^-3 (Δl /), if a larger strain amount, for example, a strain amount of about 3.0 × 10 ^-3 or more is to be obtained, the distortion generated when an electric field is applied becomes anisotropic. Therefore, there is a problem that stress is concentrated on the grain boundaries in the PZT, leading to fracture.

On the other hand, in PZT, PNZ in which part of Zr was substituted with Nb and Sn
ST material (for example, Pb _0.99 Nb _0.02 [(Zr _0.6 Sn _0.4 ) _0.94 Ti
_0.06 ] _0.98 O ₃ ) has been reported to produce large strain without fracture ("Applied Physics", Vol. 54, No. 6, (1985), pp. 591-595). As shown schematically in FIG. 4, when a PNZST material is applied with an electric field having an electric field strength of about 30 KV / cm, first, a phase transition from the antiferroelectric phase (a) to the ferroelectric phase (b) occurs. This is because the material expands greatly isotropically, and further, a piezoelectric phenomenon occurs after the phase transition, and the material expands (distorts) in the direction in which the electric field is applied. Expansion due to this phase transition ((a) →
The distortion in the electric field application direction obtained by both (b)) and the distortion due to the voltage application is about twice as large as the distortion of a normal PZT piezoelectric electrostrictive material. In this regard, the composition described above
PNZST material is very promising as a piezoelectric electrostrictive material for actuators. However, since it has a large electric field hysteresis, it has not been practically used as an actuator material.

Accordingly, an object of the present invention is to provide a piezoelectric electrostrictive material which eliminates the above-mentioned disadvantages, gives a large amount of strain, and has a small hysteresis / strain.

[Means for solving the problem]

As a result of intensive studies to achieve the above object, the present inventors have found the following.

(A) In the PNZST material, by substituting a part of Pb ²⁺ with Ba ²⁺ , the lattice constant of the crystal increases, the strain amount increases, and the hysteresis / strain decreases.

(B) If the substitution amount of Pb ²⁺ by Ba ²⁺ is too large, the antiferroelectric phase becomes unstable, and the ferroelectric phase does not return to the antiferroelectric phase even when the electric field is removed.

(C) In the PNZST material, when the amount of Ti ⁴⁺ is reduced, the electric field hysteresis / strain is reduced, but the ferroelectric phase becomes unstable, and no phase transition occurs in a small electric field.

(D) When the amount of Zr is increased in the PNZST material, the lattice constant of the crystal increases, the amount of strain increases, and the hysteresis / strain decreases, similarly to the substitution with Ba ²⁺ .

(E) In PNZST material, while increasing the amount of Zr,
When a part of b ²⁺ is replaced with Ba ²⁺ , the effect described in (d) above is further increased.

Therefore, if a part of Pb ²⁺ is replaced with Ba ²⁺ in the PNZST material and the amount of Ti ⁴⁺ is reduced in accordance with the amount of Ba ²⁺ added, the hysteresis / strain is small and the large strain is reduced. It is possible to obtain a piezoelectric electrostrictive material which always undergoes a phase transition from a ferroelectric phase to an antiferroelectric phase when applied and when an electric field is removed.

Also, if the amount of Zr in the PNZST material is increased, the hysteresis / strain is small even without Ba ²⁺ substitution, a large amount of strain is given, and when the electric field is removed, the ferroelectric phase must be changed to antiferroelectric. A piezoelectric electrostrictive material that changes into a phase can be obtained. Further substitution of Ba ²⁺ further increases the amount of strain.

The present invention has been completed based on the above findings. That is, the first piezoelectric electrostrictive material of the present invention has the following general formula: Pb _{1−x−0.5α} Ba _x Nb _α [(Zr _1−β Sn _β ) _1-y Ti _y ]
_1-α O ₃ (However, 0.01 ≦ α ≦ 0.03, 0.2 ≦ β ≦ 0.6, and 0.01 ≦
x and 004 ≦ (2/3) x + y ≦ 0.075).

Further, the second piezoelectric electrostrictive material of the present invention has the following general formula: Pb _1-x-0.5α Ba _X Nb _α (Zr _1-β Sn _β ) _1-α O ₃ (where 0.01 ≦ α ≦ 0.03, 0.2 ≦ β ≦ 0.6 and 0.06 ≦ x
≦ 0.12).

 The present invention will be described in detail below.

The composition of the first piezoelectric electrostrictive material of the present invention is represented by a general formula: Pb _{1−x−0.5α} Ba _x Nb _α [(Zr _1−β Sn _β ) _1-y Ti _y ]
_1-α O ₃ (However, 0.01 ≦ α ≦ 0.03, 0.2 ≦ β ≦ 0.6, and 0.01 ≦
x and 0.04 ≦ (2/3) x + y ≦ 0.075).

First, the Nb content α is in the range of 0.01 to 0.03. Nb is 0.
If it is less than 01, phase transition will not occur unless a high electric field is applied to the piezoelectric electrostrictive material, which is not preferable. If the amount is 0.03, the phase transition from the ferroelectric phase to the antiferroelectric phase does not occur even when the electric field is removed, and the device becomes defective. The preferred Nb content α is 0.015 to 0.025.

Next, the Sn content β is in the range of 0.2 to 0.6. Accordingly, the Zr content (1-β) is in the range of 0.4 to 0.8. Sn
Is less than 0.2 (the amount of Zr causing 0.8), the phase transition from the ferroelectric phase to the antiferroelectric phase does not occur even when the electric field is removed, resulting in failure. If Sn exceeds 0.6 (Zr is less than 0.4), phase transition will not occur unless a high electric field is applied, which is not preferable. Preferred Sn content β is 0.25-0.45,
The preferred Zr content (1-β) is from 0.55 to 0.75. If part of Pb is replaced by Ba, the hysteresis / strain is reduced. This is considered to be due to the following three reasons. That is, (a) the substitution of Ba increases the lattice constant of the crystal, and the strain increases accordingly. In particular, the lattice constant of the a-axis is 4.120Å
Above this, the distortion amount becomes 3 × 10 ⁻³ or more.

(B) BaZrO ₃ having a non-ferroelectric composition is partially formed by the introduction of Ba. At this time, Ba enters randomly into the piezoelectric electrostrictive material, so that BaZrO ₃ is locally non-uniformly formed in the piezoelectric electrostrictive material.

(C) Due to the generation of BaZrO _{3 having} a non-ferroelectric composition, the phase transition between the antiferroelectric phase and the ferroelectric phase is locally prevented.

Since the BaZrO ₃ formation sites are randomly arranged in this manner, the strength of the electric field causing the phase transition is not constant.
That is, depending on the proportion of BaZrO ₃ formed, BaZr
Phase transition occurs even in a weak electric field in a portion where O ₃ is small.
In a portion containing a large amount of ZrO ₃ , phase transition does not occur unless a relatively large electric field is applied. Therefore, the phase transition of the piezoelectric electrostrictive material as a whole is diffused, so that the phase transition occurs continuously within a certain range of electric field strength. As a result, as schematically shown in FIG. 1 (a), the strain amount of the piezoelectric electrostrictive material smoothly changes with respect to the intensity of the electric field (curve P).

On the other hand, those in which BaZrO ₃ is not formed in the piezoelectric electrostrictive material are greatly distorted by a specific electric field (Eq) (phase transition is not diffused), as schematically shown in FIG. 1 (b).

As is clear from FIGS. 1A and 1B, the hysteresis / strain of the piezoelectric electrostrictive material is reduced by partially replacing Pb with Ba. To achieve this effect, 0.01
It is necessary to introduce the above amount of Ba into the piezoelectric electrostrictive material instead of Pb. However, the addition of Ba has the effect of destabilizing the antiferroelectric phase, so if adding an amount of Ba exceeding a certain amount, the phase transition from the ferroelectric phase to the antiferroelectric phase will not occur even if the electric field is removed . Since the amount of Ba is correlated with the amount y of Ti as described later, the upper limit is also determined by the relationship with y.

In the piezoelectric electrostrictive material of the present invention, when Ti is reduced, the hysteresis is reduced. However, as the amount of Ti decreases, the ferroelectric phase becomes unstable, and the phase transition from the antiferroelectric phase to the ferroelectric phase may occur unless a high electric field is applied. Needs to be increased. On the other hand, as the amount of Ti increases, the antiferroelectric phase becomes unstable and does not return to the antiferroelectric phase even when the electric field is removed, so it is necessary to reduce the amount x of Ba. . Thus, the Ti amount y correlates with the Ba amount x.

The relationship between the Ba amount x and the Ti amount y is represented by the following equation in the first piezoelectric electrostrictive material of the present invention.

0.04 ≦ (2/3) x + y ≦ 0.075 FIG. 2 is a graph showing a possible range of the amount x of Ba and the amount y of Ti in the first piezoelectric electrostrictive material of the present invention. The Ba amount x and the Ti amount y of the first piezoelectric electrostrictive material of the present invention are directly within l ₁ , l ₂ , l ₃ and the area (not including the x-axis) surrounded by the x-axis in this graph. It is in. The reason for limiting this area will be described below.

(B) Straight line l ₁ (x = 0.01): In order to reduce the hysteresis / distortion, the Ba amount x
0.01 or more is required.

(B) From the x-axis (y> 0): The first piezoelectric electrostrictive material of the present invention contains Ti.

(C) Straight line l ₂ : This is a straight line indicating y = − (2/3) x + 0.075. In the region above this, the antiferroelectric phase becomes unstable due to excessive amounts of Ba and Ti, and does not return from the ferroelectric phase to the antiferroelectric phase even when the electric field is removed. Accordingly region is a straight line l ₂ or less.

(D) Straight line l ₃ : This is a straight line indicating y = − (2/3) x + 0.04. In the region below this, the ferroelectric phase becomes unstable due to too small amounts of Ba and Ti, and no phase transition occurs unless a high electric field is applied, which is not preferable. Accordingly region is a straight line l ₂ or more.

For the above reasons, the amount of Ba and the amount of Ti in the first piezoelectric electrostrictive material of the present invention are in the region shown in FIG. 2, that is, x = 0.
01, (2/3) x + y = 0.04, (2/3) x + y = 0.0075, and within the area enclosed by the x-axis (but not including the x-axis). Preferred ranges are 0.03 ≦ x ≦ 0.05, y>
0, 0.045 ≦ (2/3) x + y ≦ 0.07.

 Next, the second piezoelectric electrostrictive material of the present invention will be described.

The composition of the second piezoelectric electrostrictive material of the present invention is represented by a general formula: Pb _{1−x−0.5α} Ba _X Nb _α (Zr _1−β Sn _β ) _1−α O ₃ (where 0.01 ≦ α ≦ 0.03, 0.2 ≦ β ≦ 0.6 and 0.06 ≦ x
≤ 0.12).

The ranges of the content α of Nb and the content β of Sn are as described above, and the reason for this limitation is the same as the reason for limiting the content of Nb and Sn in the first piezoelectric electrostrictive material of the present invention described above. It is. Note that the Zn content (1-β) is also 0.4 to 0.8 similarly to the first piezoelectric electrostrictive material.

The amount x of Ba is in the range of 0.06 ≦ x ≦ 0.12. Although the second piezoelectric electrostrictive material does not contain Ti (y = 0), when the Ba amount x is in the range of 0.06 to 0.12, the hysteresis / strain of the piezoelectric electrostrictive material is small, and a large amount of strain is given. At the same time, a phase transition between the ferroelectric phase and the antiferroelectric phase also occurs reversibly. When x exceeds 0.12, the antiferroelectric phase becomes unstable, and the ferroelectric phase does not return to the antiferroelectric phase even when the electric field is removed. When x is less than 0.06, the ferroelectric phase becomes unstable, and unless a high electric field is applied, no phase transition occurs, which is not preferable. A more preferred range is 0.0675 ≦ x ≦ 0.105.

When the amounts of the respective elements are defined so as to fall within the ranges of α, β, x, and y described above, a piezoelectric electrostrictive material having a small hysteresis / strain and a large strain can be obtained. An electrostrictive material can reversibly perform a phase transition between an antiferroelectric phase and a ferroelectric phase by application and removal of an electric field.

Each of the first and second piezoelectric electrostrictive materials has a perovskite-type crystal structure, and Pb ²⁺ (which may be partially substituted by Ba ²⁺ ) forms an A site to form Nb _α [(Zr _{1 −β} S
n _β ) _1-y Ti _y ] _1-α forms a B site. here,
(A) Part of Pb ²⁺ forming A site is ^converted to Y ³⁺ and / or L
a ³⁺ is substituted or doped with Y ³⁺ and / or La ³⁺ , or (b) a part of Sn ⁴⁺ forming a B site is replaced with W ⁶⁺
And / or Ta ³⁺ or W ⁶⁺ and / or Ta
Doping with ³⁺ tends to reduce hysteresis / strain. In any case, the substitution amount or the doping amount is based on 100 atm% of the entire A site (or B site).
5 atm% or less. The above effects are due to Y ³⁺ , La ³⁺ , W ⁶⁺ , Ta
^{This is probably} due to the ³⁺ donor properties. In other words, if a high-valent element such as La ³⁺ or Y ³⁺ is put in place of Pb ²⁺ , or a high-valent element such as W ⁶⁺ or Ta ³⁺ is put in place of Sn ⁴⁺ , the donor effect is obtained. Appears, and the hysteresis / distortion is slightly reduced.

〔Example〕

 The present invention is described in more detail by the following examples.

Example 1, PbO as Comparative Examples 1 to 3 The starting _{material, BaCO 3, Nb 2 O 5} , ZrO 2, SnO 2, TiO
₂ , these raw material powders were composed as _follows : Pb _0.99−x Ba _x Nb _0.02 [(Zr _0.6 Sn _0.4 ) _0.94 Ti _0.06 ] _0.098
O ₃ was weighed and mixed in a ball mill for 24 hours. The obtained mixture was pre-baked at 850 to 950 ° C. for 10 hours and mixed again in a ball mill for 24 hours. 1000 kg / c of the resulting mixture
and molding at a pressure of m ^2, sintered for 2 hours at 1300 ° C., the thickness of 0.
A 3 mm sintered body was obtained. Electrode plates made of gold were formed on both surfaces of the sintered body.

A voltage was applied between the electrodes, and the amount of distortion was measured. The results are shown in FIG.

As can be seen from FIG. 3, the piezoelectric electrostrictive material having a Ba content x of 0.01 (Example 1) has clearly smaller hysteresis / strain than the piezoelectric electrostrictive material containing no Ba (Comparative Example 1) ( The amount of distortion is also large).

In the case of the Ba content x of 0.03 (Comparative Example 2) and 0.05 (Comparative Example 3), (2/3) x + y is larger than 0.075. Therefore, the strain remains even after the removal of the electric field, and cannot be used as a piezoelectric electrostrictive material.

Example 2 PbO, BaCO ₃ , Nb ₂ O ₅ , ZrO ₂ , SnO ₂ , and TiO ₂ were used as starting materials, and these raw material powders had the following composition: Pb _0.96 Ba _0.03 Nb _0.02 [(Zr _0.65 Sn _0.35 ) _0.96 Ti _0.04 ] _0.98 O ₃ was weighed and mixed in a ball mill for 24 hours. The obtained mixture was pre-baked at 850 to 950 ° C. for 10 hours and mixed again in a ball mill for 24 hours. 1000 kg / c of the resulting mixture
and molding at a pressure of m ^2, sintered for 2 hours at from 1,260 to 1,290 ° C.,
A sintered body having a thickness of 0.3 mm was obtained. Electrode plates made of gold were formed on both surfaces of the sintered body.

A voltage was applied between the electrodes, and the strain amount and hysteresis were measured. Further, the lattice constants of the a-axis and c-axis of each sample were measured. The results are shown in Table 1.

As can be seen from Table 1, at the sintering temperature of 1260 to 1290 ° C., the strain amount (Δl /) is clearly as large as 3 × 10 ⁻³ or more, and the hysteresis is small. In these cases, the lattice constant of the a-axis is 4.120 ° or more.

Example 3 PbO, BaCO ₃ , Nb ₂ O ₅ , ZrO ₂ , SnO ₂ , and TiO ₂ were used as starting materials, and these raw material powders had the following composition: Pb _0.99−x Ba _x Nb _0.02 [(Zr _0.65 Sn _{0.35 1-y} Ti _y ]
_It was weighed to _0.98 O ₃ and mixed in a ball mill for 24 hours. The obtained mixture was pre-baked at 850 to 950 ° C. for 10 hours and mixed again in a ball mill for 24 hours. 1000 kg / c of the resulting mixture
and molding at a pressure of m ^2, sintered for 2 hours at from 1,260 to 1,290 ° C.,
A sintered body having a thickness of 0.3 mm was obtained. Electrode plates made of gold were formed on both surfaces of the sintered body.

A voltage was applied between the electrodes, and the strain amount and hysteresis were measured. Further, the lattice constants of the a-axis and c-axis of each sample were measured. The results are shown in Table 2.

As is evident from Table 2, the strain amount increases as the Zr amount increases, and the strain amount further increases as the Ba amount increases.

Example 4 PbO, BaCO ₃ , Nb ₂ O ₅ , ZrO ₂ , SnO ₂ , and TiO ₂ were used as starting materials, and these raw material powders had the following composition: Pb _0.99−x Ba _x Nb _0.02 [(Zr _0.7 Sn _0.3 ) _1-y Ti _y ] _0.98 O
_The mixture was weighed to ₃ and mixed in a ball mill for 24 hours. The obtained mixture was pre-baked at 850 to 950 ° C. for 10 hours and mixed again in a ball mill for 24 hours. 1000 kg / c of the resulting mixture
and molding at a pressure of m ^2, sintered for 2 hours at from 1,260 to 1,290 ° C.,
A sintered body having a thickness of 0.3 mm was obtained. Electrode plates made of gold were formed on both surfaces of the sintered body.

A voltage was applied between the electrodes, and the strain amount and hysteresis were measured. Further, the lattice constants of the a-axis and c-axis of each sample were measured. The results are shown in Table 3, FIG. 5, and FIG.

As is clear from Table 3, when the Zr amount is increased to 0.7, the distortion amount is increased even when the Ba amount is 0. Further, it is recognized that the strain amount is further increased by increasing the Ba amount.

As is clear from FIG. 5, when the amount of Ba increases,
The width of the hysteresis of the distortion amount decreases. Further, as is clear from FIG. 6, when the Zr content is as large as 0.65, the lattice constant of the a-axis is 4.12 ° or more, and further increases as the Ba content increases.

Reference Example PbO, Nb ₂ O ₅ , ZrO ₂ , SnO ₂ , and TiO ₂ were used as starting materials, and these raw material powders had the following composition: Pb _0.99 Nb _0.02 [(Zr _1−β Sn _β ) _1-y Ti _y ] _0.98 O ₃ were weighed so that, by mixing in a ball mill for 24 hours. The obtained mixture was pre-baked at 850 to 950 ° C. for 10 hours and mixed again in a ball mill for 24 hours. 1000 kg / c of the resulting mixture
and molding at a pressure of m ^2, sintered for 2 hours at from 1,260 to 1,290 ° C.,
A sintered body having a thickness of 0.3 mm was obtained.

The content of Zr and Ti and the firing temperature of each sample are as follows.

Sample No. Zr Ti firing temperature 1 0.55 0.065 1300 ° C 2 0.55 0.07 1300 ° C 3 0.6 0.06 1300 ° C 4 0.65 0.05 1290 ° C 5 0.7 0.04 1290 ° C 6 0.75 0.04 1280 ° C Formed. A voltage was applied between the electrodes, and the strain amount and hysteresis were measured. Further, the lattice constants of the a-axis and c-axis of each sample were measured.

FIG. 7 shows the lattice constant (a-axis) and strain (Δl /
). As is clear from FIG.
When it exceeds 0.6, the amount of strain increases rapidly. As a result of the study, it was found that when the Zr amount was 0.63 or more, the strain amount was surely increased. It was also found that the firing temperature had to be lowered somewhat as the amount of Zr increased. For example, when the amount of Zr is 0.65 or more, 1290 ° C. is appropriate, and when the amount of Zr reaches 0.75, it is appropriate to keep the temperature as low as 1280 ° C.

FIG. 8 shows the hysteresis of the strain amount of the samples Nos. 4 to 6. It can be seen that even if the amount of distortion increases, the width of the hysteresis does not become relatively large.

〔The invention's effect〕

As described in detail above, the piezoelectric electrostrictive material of the present invention gives a large amount of strain and has a small hysteresis width, and is suitable as a material for various actuators requiring a large amount of displacement.

[Brief description of the drawings]

FIGS. 1A and 1B are graphs schematically showing the amount of strain of a piezoelectric electrostrictive material when an electric field is applied to the piezoelectric electrostrictive material, and FIG. Indicates the case,
(B) shows the case of the conventional PNZST material, and FIG. 2 shows the Ba composition in the composition of the first piezoelectric electrostrictive material of the present invention.
FIG. 3 is a graph showing a region where the amount (x) and the amount of Ti (y) can be taken; FIG. 3 is a graph showing the amount of strain when an electric field is applied to the piezoelectric electrostrictive materials of Example 1 and Comparative Examples 1 to 3; FIG. 4 is a schematic view showing the two-stage distortion of the PNZST material caused by the application of an electric field. FIG. 5 is a diagram showing the piezoelectric electrostrictive material when an electric field is applied to the piezoelectric electrostrictive material of Example 4. 6 is a graph showing the amount of strain, FIG. 6 is a graph showing the relationship between the amount of Ba ²⁺ and the lattice constant (a-axis) of the piezoelectric electrostrictive material of Example 4, and FIG. FIG. 8 is a graph showing the relationship between the lattice constant (a-axis) of the strained material and the strain amount. FIG. 8 is a graph showing the strain amount of the piezoelectric electrostrictive material when an electric field is applied to the piezoelectric electrostrictive material of the reference example. is there.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Minoru Noguchi 1-4-1 Chuo, Wako-shi, Saitama Prefecture Inside Honda R & D Co., Ltd. (72) Kenji Uchino 4200-2 Totsuka-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture Fujiwa Totsuka Corp. Room 103 (56) References Э. Х. Бцрке et al. “ЭЛЕКТРОКАЛОРИЙ ЭФ ФЕКТВ ТВЕРДЫХ РАСТ ВОРАХ Pb (Zr, Sn, Ti) 03 Ｐ Pb (Hf, Sn, Ti) 03, ФИЗИКА ТВЕРЛОГО ТЕ ЛА, (1987) Vol. 29, No. 8, No. 2284- 2289 "(58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/42-35/49 H01L 41/18-41/187 CA (STN) REGISTRY (STN)

Claims (2)

(57) [Claims] 1. The following general formula: Pb _1-x-0.5α Ba _x Nb _α [(Zr _1-β Sn _β ) _1-y Ti _y ]
A piezoelectric electrostrictive material having a composition represented by _1-α O ₃ (where 0.01 ≦ α ≦ 0.03, 0.2 ≦ β ≦ 0.6, 0.01 ≦ x, and 0.04 ≦ (2/3) x + y ≦ 0.075) . 2. The following general formula: Pb _1-x-0.5α Ba _X Nb _α (Zr _1-β Sn _β ) _1-α O ₃ (where 0.01 ≦ α ≦ 0.03, 0.2 ≦ β ≦ 0.6 and 0.06 ≦ x
≦ 0.12) A piezoelectric electrostrictive material having a composition represented by the formula: