JPH07257924A - Piezoelectric material - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric material having sufficient displacement performance and at least >=200 deg.C Curie temp. and with the deterioration of displacement reduced even when driven in a high electric field exceeding an anti-electric field. CONSTITUTION:The piezoelectric material is a composition expressed by (Pb1-xMx)1-(z-u)/2((ZryTi1-y)1-(z+u)AyBu)O3. In the formula, M is at least one kind among Sr, Ca and Ba, 0<x<=0.25 and 0<y<=0.7, A is a metallic element forming pentavalent ion, B is a metallic element forming a trivalent ion, A and B are formed by substituting a part of the (ZryTi1-y), 0.2<=100X(z-u)<=2.0 where the substitution amt. of A is 100Xzmol% and that of Bis 100Xumol%, and an excess metallic element not contained in the crystal lattice is not present. The deterioration of displacement of a piezoelectric element formed of the composition is reduced even when the element is driven for a long time in a high electric field.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric material which can be used for an actuator, particularly for a high load actuator utilizing domain inversion.

[0002]

2. Description of the Related Art Lead zirconate titanate (PZ
A piezoelectric material whose main component is T) is known. This PZ
Compared to other piezoelectric materials, T ceramics has a large piezoelectric constant and is excellent in displacement performance. Therefore, the PZT-based piezoelectric material has been widely applied to a minute displacement element, an ultrasonic vibration generating element, etc. by utilizing its characteristics.

The improvement aimed at improving the characteristics of PZT is to replace the A site (Pb) with Sr, Ca, etc.
A method of adding Nb, Ta or the like to B site (Zr, Ti) is known, and there is a disclosure of a composition combining them (for example, JP-A-62-298192, JP-A-4-260062, and Kaihei 5-148016).

In recent years, these PZT piezoelectric elements have been studied for development into high-load actuators which are driven under high-load conditions and which utilize 90 ° domain reversal in order to obtain a larger amount of displacement. However, in the above application, the piezoelectric element is subjected to strict driving conditions, and therefore displacement of the piezoelectric material deteriorates due to long-term driving, which is a serious problem. It is considered that the cause of this displacement deterioration is that the domain wall is pinned by space charge and the domain inversion is suppressed.
Therefore, it is considered effective to suppress deterioration by adding a donor element that reduces oxygen defects, which is a cause of space charge generation, to the piezoelectric material. However, when the above donor element is added (externally added) to the stoichiometric composition,
A part of the excess B site ions is precipitated as an oxide at the grain boundaries. The oxide deposited on the grain boundaries causes pinning of the domain wall, and cannot sufficiently suppress displacement deterioration of the piezoelectric material. Further, in the above-mentioned single substitution of the donor, the effect of suppressing the deterioration was not so great although the cause was not clear.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has sufficient displacement performance and is capable of performing displacement even when driven for a long time under a high electric field exceeding a coercive electric field. The purpose is to obtain a piezoelectric material with little deterioration.

[0006]

The piezoelectric material of the present invention comprises:
(Pb _1-x M _x ) _{1- (ZU) / 2} {(Zr _y Ti _1-y ) <sub>1- (z
+ u)</sub> A _z B _u } O _{3 wherein} M is S
It consists of at least one of r, Ca and Ba, and 0 <
x ≦ 0.25, 0 <y ≦ 0.7, A is a metal element that becomes a pentavalent ion, B is a metal element that becomes a trivalent ion, and A and B are (Zr _y Ti _1-y ) When the amount of substitution of A is 100 × z mol% and the amount of substitution of B is 100 × u mol%, 10
0 × z and 100 × u are 0.2 ≦ 100 × (z−u)
The composition is in the range of ≦ 2.0, and is characterized in that there is no excess metal element not included in the crystal lattice.

The piezoelectric material of the present invention is made of Pb _1-x M _x (Zr
_The basic composition is _y Ti _1-y ) O ₃ . M in the above formula
Is at least one selected from Sr, Ca and Ba, and x replaces Pb with M in an amount in the range of 0 <x ≦ 0.25. When the substitution amount index x becomes larger than 0.25, that is, when the amount of Pb in the formula decreases, Tc
(Curie temperature) decreases, and in some cases (for example, S
In r), the temperature becomes 100 ° C. or less and it becomes unpractical, which is not preferable.

The index y of the substitution amount in the above formula is a value showing the ratio of Zr to Ti at the B site, and 0 <y ≦ 0.7.
Is the range. If y exceeds 0.7 and becomes large, a ferroelectric phase may not be formed, which is not preferable. PZT is M
Since the displacement characteristic becomes maximum near PB (morphotropic phase boundary), y is 0.52 of the composition near that.
It is desirable that ≦ y ≦ 0.60.

A feature of the present invention is that the B site (Z
A part of r _y Ti _1-y ) is substituted with a metal element A that becomes a pentavalent ion and a metal element B that becomes a trivalent ion. Then, the substitution amount is within a specific range. That is, the substitution amount of the metal element A that becomes pentavalent ions is expressed as 100 × u mol%. The substitution amount B of the metal element that becomes trivalent ions is expressed as 100 × u mol%. The addition amount of both is set in the range of 0.2 ≦ 100 × (z−u) ≦ 2.0. Donor ions have a function of reducing oxygen vacancies, and acceptor ions have a function of increasing oxygen vacancies. Therefore, when the difference in mol% between the two ions is in the range of 0.2 ≦ 100 × (z−u), the effect of reducing oxygen defects is small, and displacement deterioration cannot be sufficiently suppressed. On the other hand, when the difference in mol% between the two ions exceeds 2.0, the donor becomes excessive, and the charge imbalance becomes too large, so that the deterioration suppressing effect is deteriorated, which is not preferable.

The above 100 × z amount is preferably in the range of 0.2 to 2.5 in terms of mol%. 10
When the amount of 0 × z is 0.2 mol% or less, the amount of donor substitution is too small and the deterioration suppressing effect is not exhibited, which is not preferable. Further, when the amount of 100 × z exceeds 2.5 mol%, the temperature change of the displacement characteristic becomes large. For example, assuming an automobile actuator (operating temperature range: −50 to 150 ° C.), the temperature range is within the required range. It is not preferable because it will not drive stably.

The above amount of 100 × u is, for example, 2.3.
It is preferably in the range of not more than mol% (not including 0). The amount of 100 × u is 0.2 ≦ 100 × (z−u) ≦
In order to satisfy 2.0 and 100 × z ≦ 2.5 at the same time, it is necessary to satisfy 0 <100 × u ≦ 2.3. As the above A, a metal element such as Nb, Ta, V or Sb can be used. Also, the original valence of the site (4)
In terms of larger size (donor), hexavalent W and U are also available.

As the B, a metal element such as Fe or Cr can be used. In addition, in terms of being smaller than the original valence of the site (4 valence) (acceptor), divalent Ni,
Zn and Mn can also be used. As the raw material of the above-mentioned pentavalent ion and trivalent ion, carbonate can be used in addition to oxide. Further, when manufacturing the piezoelectric material of the present invention, it is preferable to use a pad material having the same composition as that of the piezoelectric material in order to suppress compositional variation during firing. That is, if the composition of the pad material and that of the sample to be fired are different, mass transfer between them easily occurs during firing, and it is difficult to obtain a fired body according to the charged composition. On the other hand, if the composition is the same, mass transfer does not easily occur, so that it is possible to obtain a fired product according to the charged composition.

The firing temperature at the time of manufacturing this piezoelectric material is 100.
0 to 1300 ° C, preferably 1150 to 1250 ° C. If the firing temperature is 1000 ° C. or lower, a dense fired body cannot be obtained, and if it is 1300 ° C. or higher, the lead component in the composition evaporates significantly, which is not preferable.

[0014]

The piezoelectric material of the present invention is (Pb _1-x M _x )
_{1- (ZU) / 2} {(Zr _y Ti _1-y ) _{1- (z + u)} A _z B _u } O
_It has a composition of ₃ . In the formula, (Zr _y Ti _1-y ) is partially substituted by a metal element A which becomes a pentavalent ion and a metal element B which becomes a trivalent ion. Then, the substitution amount of each metal element of the pentavalent ion and the trivalent ion is set in a specific range, and the composition is in a state in which it does not exist in excess in the crystal lattice.

In the piezoelectric material of this composition, the donor ion of A has a function of reducing oxygen vacancies and the acceptor ion of B has a function of increasing oxygen vacancies. It has the same displacement performance as the above and has a smaller particle size than the single addition system. Although the cause is not clear, displacement deterioration can be suppressed. For example, in a system in which both pentavalent ion Nb and trivalent ion Fe are substituted, the particle size becomes smaller than that in the system in which only Nb is added,
Moreover, it has a displacement performance equal to or higher than that of the Nb single addition system. Furthermore, the system in which both are replaced is less likely to undergo displacement deterioration than the piezoelectric element of the single addition system.

When a donor or an acceptor is externally added to PZT having a stoichiometric composition, excess B site ions are precipitated at the grain boundaries to suppress the movement of the domain wall even if the amount is very small. The lower displacement performance is deteriorated and the displacement is easily deteriorated. Also, if the crystal grain size is large, the cause is not obvious, but displacement deterioration is likely to occur. On the other hand, the substitution of both does not suppress the movement of the domain wall because there is no precipitation at the grain boundaries, and the particle size becomes smaller than that of the single addition, so that the problem of displacement deterioration can be solved.

With the above composition, the piezoelectric material of the present invention is optimal as a high-load actuator material having excellent displacement performance and little displacement deterioration.

[0018]

EXAMPLES The present invention will be described below with reference to examples. (Synthesis of Powder) First, raw material powders of PbO, SrO, TiO ₂ , and Zr
O ₂ , Nb ₂ O ₅ , and Fe ₂ O ₃ were weighed in predetermined amounts shown in Table 1 and thoroughly mixed by a dry method (note that in the examples, M,
Sr, Nb, and Fe were used as the elements of A and B, respectively). Then, calcination was performed at 700 to 900 ° C. for 1 to 10 hours, and then wet pulverization was performed for 24 hours using a ball mill (ZrO ₂ balls). The obtained powder was spray-dried and granulated to obtain each sample powder shown in Table 1. (Preparation of Sample) Each sample powder obtained by the above method was mixed with a binder and the like, preformed by uniaxial pressure and then CIP molded to obtain a pellet-shaped green compact. This green compact 600
After degreasing by heating at ℃ for 30 minutes, 1150 to 1250
Calcination was carried out for 2 hours. Note that each sample was baked in a state where it was completely embedded in a pad material manufactured with the same composition as each sample. Next, both surfaces of each of the obtained fired bodies were polished, and electrodes were provided on the polished surfaces by silver paste baking. And 100
Polarization treatment (1-5kV / mm electric field 1
It was applied for 0 minutes) and used as a measurement sample. Example No. 1-1
1, Comparative Example No. 20-27. Table 1 shows the prepared PZ
The x, y, z, u and zu values showing the composition of T and the Tc (Curie temperature) of the sample are shown. (Durability test) First, prior to durability test, compressive stress 20MP
An electric field of −400 to 1600 V / mm was applied to the sample at a, and changes in strain amount and polarization amount at that time were measured. Then, the amount of strain per unit polarization change before the durability test, that is, the apparent g constant under a large amplitude electric field was obtained. Next, under a special AC electric field exceeding the coercive electric field (1-2 kV / m
An endurance test of driving 10 ⁷ times in m) was performed, and thereafter, changes in strain and polarization were measured under the same conditions as above. Then, the g constant before and after the durability test was compared, and the g constant retention rate was calculated. The results are shown in Table 1.

[0019]

[Table 1]

As shown in Table 1, this embodiment No. 1-1
In No. 1, since the 100 × (z−u) value is within the range of the present invention, the g-constant retention rate is 90% or more, indicating that displacement deterioration is small. On the other hand, Comparative Example No. 20 to 27 of 100
When the x (z−u) value is out of the range of the present invention, the g constant retention rate is 90% or less, and the displacement deterioration is large. That is, Comparative Example No. 24 and 27 are examples that do not include the B component. Comparative Example No. 22 is an example in which the B component is too much, and Comparative Example No. Nos. 20 and 22 are examples in which the amounts of both A and B components are the same, and Comparative Example No. Nos. 25 and 26 are examples in which additives were externally added.

As a driving method of the actuator, charge control without hysteresis is drawing attention. In that case, the amount of distortion with respect to a fixed amount of charge is important. Therefore, the g constant serves as a guideline for deterioration of the displacement, and the fact that the g constant does not decrease means that the deterioration does not occur. In this embodiment, the holding rate of the g constant is 90% or more, and it is possible to withstand the use of the above driving method.

[0022]

EFFECTS OF THE INVENTION The piezoelectric material of the present invention has a large amount of displacement and can suppress deterioration of displacement by setting the above composition range. As a result, it can be used in a wide temperature range (up to 150 ° C.) and an actuator that requires a large amount of displacement, such as an automobile actuator.

[Procedure amendment]

[Submission date] April 19, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

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[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

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[0006]

The piezoelectric material of the present invention comprises:
(Pb _1-x M _x ) _{1- (zu ) / 2} {(Zr _y Ti _1-y ) <sub>1- (z
+ u)</sub> A _z B _u } O _{3 wherein} M is S
It consists of at least one of r, Ca and Ba, and 0 <
x ≦ 0.25, 0 <y ≦ 0.7, A is a metal element that becomes a pentavalent ion, B is a metal element that becomes a trivalent ion, and A and B are (Zr _y Ti _1-y ) When the amount of substitution of A is 100 × z mol% and the amount of substitution of B is 100 × u mol%, 10
0 × z and 100 × u are 0.2 ≦ 100 × (z−u)
The composition is in the range of ≦ 2.0, and is characterized in that there is no excess metal element not included in the crystal lattice.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0014

[Correction method] Change

[Correction content]

[0014]

The piezoelectric material of the present invention is (Pb _1-x M _x )
_{1- (zu ) / 2} {(Zr _y Ti _1-y ) _{1- (z + u)} A _z B _u } O
_It has a composition of ₃ . In the formula, (Zr _y Ti _1-y ) is partially substituted by a metal element A which becomes a pentavalent ion and a metal element B which becomes a trivalent ion. Then, the substitution amount of each metal element of the pentavalent ion and the trivalent ion is set in a specific range, and the composition is in a state in which it does not exist in excess in the crystal lattice.

Claims (1)

[Claims] 1. (Pb _1-x M _x ) _{1- (ZU) / 2} {(Zr _y
Ti _1-y ) _{1- (z + u)} A _z B _u } O _{3 wherein} M is at least one of Sr, Ca and Ba, and 0 <x ≦ 0 0.25, 0 <y ≦ 0.7, and A is 5
A metal element to be a valent ion, B is a metal element to be a trivalent ion, A and B are those partially substituted in (Zr _y Ti _1-y ), and the substitution amount of A is 100 × z mol% and the substitution amount of B is 100 × u mol%,
For 100 × z and 100 × u, 0.2 ≦ 100 × (z−
u) A piezoelectric material comprising a composition in the range of ≦ 2.0, wherein there is no excess metal element not included in the crystal lattice.