JPH07215761A - Piezoelectric porcelain composition and its production - Google Patents

Abstract

PURPOSE:To obtain a piezoelectric porcelain compsn. excellent in characteristics as a laminate type piezoelectric actuator. CONSTITUTION:In a piezoelectric porcelain compsn. having a compsn. represented by the formula, Pb(ZrxTi1-x)O3 (where 0.52<=x<=0.59) as the basic compsn., at least one among Ca, Sr and Ba is substd. for 2-12mol% of Pb atoms and Sb, at least one among Mn, Fe and Cr and Al are incorporated by 0.1-2.0wt.% (expressed in terms of Sb2O3), 0.01-0.5wt.% (expressed in terms of oxide) and 0.001-0.04wt.% (expressed in terms of Al2O3), respectively. In a process for pulverizing a mixture, a ball mill not cont,g. Al, e.g. a zirconia ball mill is used. Such characteristics as the electric resistivity, the mechanical strength and the electromechanical coupling factor are considerably improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition containing lead zirconate titanate as a main component and a method for producing the same, and in particular, it has a high sintering density and a large piezoelectric characteristic, and has an insulating property And a piezoelectric ceramic composition excellent in mechanical strength and a method for producing the same.

[0002]

2. Description of the Related Art As a piezoelectric ceramic body, a PZT type piezoelectric ceramic composition containing lead zirconate titanate as a main component, which is composed of oxides of lead, zirconium and titanium, is widely known. It is used as a laminated piezoelectric actuator that expands and contracts. The manufacturing method is generally that the constituents are weighed to form a mixture, the mixture is crushed by a ball mill, and then molded and sintered (for example, see Electronic Material August 1988, P85). .

[0003]

By the way, it has been considered that the PZT-based piezoelectric ceramic composition has a relatively long history and a manufacturing method thereof has been established. However, in reality, there are problems that electric resistivity is relatively low, mechanical strength such as bending strength is low, and electromechanical coupling coefficient (conversion efficiency) is low. In particular, there is a problem that reliability is lowered when a laminated piezoelectric actuator is formed, but the cause has not been clarified at present.

The present invention focuses on the above problems,
It was created to solve this effectively. An object of the present invention is to provide a piezoelectric ceramic composition having a relatively high electric resistivity, a high mechanical strength such as bending strength, and a high electromechanical coupling coefficient, and a method for producing the same.

[0005]

[Summary of the first invention, in order to solve the above problems, a composition formula _{Pb (Zr X Ti 1-x} ) O
_In a piezoelectric ceramic composition having a basic composition represented by ₃ (provided that 0.52 ≦ X ≦ 0.59), 2 to 12 mol% of the Pb atom is replaced with at least one of Ca, Sr and Ba. Then, Sb is converted to Sb ₂ O ₃ for 0.1 to 2.
0% by weight, 0.01 to 0.5% by weight of at least one of Mn, Fe, and Cr converted to oxides, and Al as A
It is configured so as to contain 0.001 to 0.04% by weight in terms of l ₂ O ₃ .

In order to solve the above problems, a second invention is a composition formula Pb (Zr _X Ti _1-x ) O ₃ (however, 0.52).
≦ X ≦ 0.59) in the method for producing a piezoelectric ceramic composition having a basic composition represented by 2 to 1 of the Pb atoms.
A substance containing Ca, Sr or Ba is weighed so that 2 mol% is replaced with at least one of Ca, Sr and Ba, and S
b converted to Sb ₂ O ₃ 0.1 to 2.0% by weight, M
At least one of n, Fe, and Cr should be contained in an amount of 0.01 to 0.5 wt% in terms of oxide, and 0.001 to 0.04 wt% in terms of Al in terms of Al ₂ O _3. Each is weighed and mixed with the basic raw material to form a mixture, and the mixture is crushed by a ball mill substantially free of Al,
This crushed product is configured to be sintered.

[0007]

The present inventor has accomplished the present invention by selecting an optimum composite composition as shown below and reviewing the manufacturing method. First, the optimum composite structure is Pb in the composition near the phase boundary between lead titanate and lead zirconate and C
Substituting at least one of a, Sr and Ba, and replacing Sb with S
b ₂ O _{3 in} a proper amount, at least one of Mn, Fe, and Cr is added in a trace amount, and Al in a form of Al ₂ O ₃ is added in a trace amount. The electrical conductivity, which is the reciprocal of the resistivity, can be lowered, and the mechanical strength and the electromechanical coupling coefficient can be increased. Since all of Mn, Fe, and Cr to be added are in very small amounts, they can be effectively mixed by adding them to other solid powder raw materials in a solution form.

Next, the reasons for limiting the components of the present invention will be described. Pb
When the ratio of substituting a part of atoms with at least one of Ca, Sr and Ba is less than 2 mol%, the piezoelectric strain constant (−
d ₃₁ ) is as small as 150 × 10 ⁻¹² (m / v) or less, and 1
If it exceeds 2 mol%, the Curie temperature is lowered, and the temperature stability when used as a piezoelectric element is poor. The relative permittivity is 30
It is as large as 00 or more, and when the piezoelectric element is used, the electrostatic capacitance becomes too large and the driving circuit is burdened. When the amount of Sb added is less than 0.1% by weight in terms of Sb ₂ O ₃ , the improvement of the piezoelectric constant is insufficient, and when it exceeds 2.0% by weight, the electromechanical coupling constant Kp is increased. Is reduced. Mn, F
When the addition amount of at least one of e and Cr is less than 0.01% by weight in terms of each oxide, the improvement of the electrical resistivity is insufficient, and when it exceeds 0.5% by weight. In particular, the relative permittivity ε ^T ₃₃ and the electromechanical coupling constant Kp are remarkably lowered, and the piezoelectric strain constant (−d ₃₁ ) becomes too small. In particular, the effect of adding Mn is great, but when it is less than 0.01% by weight, the mixing of Mn is difficult and the effect of improving the electrical resistivity is small. In the present invention, the effect of adding Al is remarkable,
If it is less than 0.001% by weight in terms of l ₂ O ₃ I, abnormal grain growth occurs and the bending strength is insufficiently improved. On the other hand, if it exceeds 0.04% by weight, the piezoelectric strain constant and the electrical resistivity decrease, and the bending strength also decreases.

Further, the present invention has been made by obtaining the knowledge that the step of pulverizing a mixture of constituent compositions is particularly important in order to stably and stably produce the above-mentioned composite ceramic composition. It is a thing. That is, at the time of pulverizing the mixture, the mixture is pulverized by a ball mill using a ball and a mill pot that do not substantially contain an Al component, which is one of the constituent elements, so that the abrasion powder of the ball mill does not affect the Al content. The Al content is controlled within the optimum range of a very small amount.

As described above, by using a ball mill in which the respective contents of the constituent compositions are sufficiently controlled and which does not substantially contain an Al component at the time of pulverizing the mixture, the electric resistivity is relatively high, that is, the electric conductivity. It is possible to obtain a piezoelectric ceramic composition having a relatively low value and a high mechanical strength such as transverse strength and a high electromechanical coupling coefficient. Although there are inorganic and organic materials for the ball mill that do not substantially contain an Al component, considering the hardness, it is optimal to use an inorganic material, particularly a zirconia ball mill composed of zirconia balls and zirconia pots.

Here, the term "substantially free of Al component" means that
All materials always contain a very small amount of Al, even if they are composed of pure materials. However, in the field of powder metallurgy, Al is a pure material without Al components. It refers to the state of not containing ingredients. For example, even the above-mentioned zirconia ball mill contains a very small amount of Al component as an impurity, but it means that this amount of Al component can be ignored.

[0012]

EXAMPLES An example of a piezoelectric ceramic composition and a method for producing the same according to the present invention will be described in detail below with reference to the accompanying drawings. First, lead oxide (PbO), strontium carbonate (SrCO
₃ ), titanium oxide (TiO ₂ ), zirconium oxide (Z
rO ₂ ), antimony oxide (Sb ₂ O ₃ ), manganese oxide (MnO ₂ ) and aluminum oxide (Al ₂ O ₃ ) are represented by the chemical formula (Pb _1-y Sr _y ) (Zr _x Ti _1-x ) O ₃ +
0.3 wt% Sb ₂ O ₃ +0.05 wt% MnO ₂ + Z
wt% Al ₂ O ₃ (where 0.02 ≦ y ≦ 0.12 and 0.52 ≦ X ≦ 0.59) is weighed in a predetermined ratio, and the mixture is mixed with ethyl alcohol as a solvent. The mixture was mixed for 2 hours with a ball mill substantially free of Al component, for example, a zirconia ball mill having a Vickers hardness far higher than that of alumina balls. In this case, the Zwt% of Al ₂ O ₃ is 0 to about 0.3% by weight.
(Wt%) was variously selected and weighed. The obtained mixture is dried at 100 ° C. for 5 hours, preliminarily molded, and then calcined in air at 850 ° C. for 2 hours, using a ball mill substantially free of the Al component described above, for example, a zirconia ball mill. And crushed for 2 hours. After granulating this pulverized product, a molded product having a diameter of 20 mm and a length of 15 mm was formed by press molding.

The compact was sintered in oxygen in a container made of alumina or magnesium in oxygen at three temperatures of 1230 ° C., 1260 ° C. and 1280 ° C. for 5 hours. The obtained sintered body was cut and polished to obtain a piezoelectric ceramic composition having a diameter of 16 mm and a thickness of 0.8 mm. An electrode made of Cr-Au was formed on both surfaces of this composition, and the electrode was set to 3 KV / in silicon oil.
The polarization treatment was performed by applying a DC voltage of mm. Various tests were performed on the piezoelectric ceramic composition thus formed,
The evaluation was performed.

First, the densities of the piezoelectric ceramic compositions when various amounts of Al ₂ O ₃ were added were examined. Figure 1 shows Al ₂ O ₃
3 is a graph showing the density of the piezoelectric ceramic composition with respect to the addition amount of As is clear from this graph, the smaller the amount of Al ₂ O ₃ added, the higher the density and the more favorable the state becomes.
When the amount of Al ₂ O ₃ added was increased, the density of the composition gradually decreased irrespective of the sintering temperature, especially when the theoretical density by X-ray diffraction decreased from 7.8 to 3%. It is found that the density is drastically reduced when the added amount of, that is, the added amount exceeds 0.04% by weight and becomes large. When the sintering temperature is variously changed to 1230 ° C., 1260 ° C., and 1280 ° C., the higher the sintering temperature is, the less the decrease in the density is, but the addition amount of Al ₂ O ₃ is still less.
The phenomenon in which the density sharply decreases when the content exceeds 04% by weight is common.

Next, the electric conductivity of the produced piezoelectric ceramic composition was examined. FIG. 2 is a graph showing the relationship between the added amount of Al ₂ O ₃ and the electric conductivity. In addition, the composition used in the test is one that is sintered at a temperature of 1260 ° C.
Two test temperatures, 150 ° C. and 170 ° C., are used. The less is the addition amount of Al ₂ O ₃ As is apparent from this graph, the electrical conductivity is reduced (electrical resistivity increases reversed), showed good values, the addition of Al ₂ O ₃ in the opposite As the amount increases, the electrical conductivity increases,
In particular, when the amount of Al ₂ O ₃ added exceeds 0.04% by weight, the electric conductivity also increases considerably, which is not preferable.

Next, the dielectric constant and the dielectric constant ratio of the produced piezoelectric ceramic composition were examined. FIG. 3 is a graph showing the relationship between the added amount of Al ₂ O ₃ and the dielectric constant, and FIG. 4 is a graph showing the relationship between the added amount of Al ₂ O ₃ and the dielectric constant ratio. In the graph, ε * represents ε (dielectric constant) of the composition before polarization (not oriented) to which a DC voltage of 3 KV / mm was not applied,
ε ^T ₃₃ is ε in the 33 direction after polarization and is ε (dielectric constant) in the state where no stress is applied. Also, ε ^T ₃₃
/ Ε * is related to the degree of orientation after polarization.

As is apparent from the graph shown in FIG. 3, the composition ε polarized is more preferable than the composition ε * which is not polarized.
It turns out that ^T ₃₃ has an overwhelmingly high dielectric constant and is preferable. Also, focusing on the polarized composition ε ^T ₃₃ ,
The higher the sintering temperature, the higher the permittivity and the better. Also,
The dielectric constant increases as the added amount of Al ₂ O ₃ (analysis value) increases.
It becomes small, and especially when the addition amount exceeds 0.04% by weight, the dielectric constant sharply decreases, which is not preferable. Therefore, Al ₂
The amount of O ₃ added is set to be smaller than 0.04% by weight.

According to the graph shown in FIG. 4, Al ₂
As the amount of O ₃ added increases, the dielectric constant ratio decreases,
It was found that by setting the addition amount to be less than about 0.04% by weight, the dielectric constant ratio was maintained at about 1.6 or more, and good results could be obtained. Further, regarding the sintering temperature, it is found that the higher the sintering temperature is, the higher the dielectric constant ratio is, which is preferable in the range where the added amount is less than 0.04% by weight.

Next, the electromechanical coupling coefficient of the produced piezoelectric ceramic composition, that is, the energy conversion efficiency was examined. Fig. 5 shows the amount of Al ₂ O ₃ added and the electromechanical coupling coefficient K.
It is a graph which shows the relationship with p. As is clear from the graph, the smaller the amount of Al ₂ O ₃ added, the higher the value of Kp, indicating a good result, and the smaller the amount of addition, the lower the value of Kp. In particular, when the amount added is less than about 0.04% by weight, the value of Kp sharply decreases, which is not preferable.

Next, the average result of the produced piezoelectric ceramic composition
The grain size and the bending strength were examined. Figure 6 shows Al₂ O
₃ FIG. 7 is a graph showing the relationship between the amount of addition of Cu and the average crystal grain size.
Is Al ₂ O₃ Graph showing the relationship between the addition amount of B and the bending strength
Is. The sintering temperature of the composition was 1260 ° C.
It

According to these graphs, the smaller the amount of Al ₂ O ₃ added, the smaller the average crystal grain size, and the greater the bending strength, which is a good result. When the amount of Al ₂ O ₃ added is set to substantially zero, abnormal grain growth in which crystal grains grow abnormally large is not preferable. Further, if this abnormal grain growth occurs, the bending strength also decreases, which is not preferable. The addition amount of Al ₂ O ₃ that causes this abnormal grain growth is about 0.001% by weight. To prevent the occurrence of this abnormal grain growth and maintain a high bending strength, 0.001% by weight is required. Mostly Al ₂ O ₃
Need to be added. When the amount of Al ₂ O ₃ added is more than about 0.04% by weight, the grain boundary fracture region shifts to the intragranular fracture region.

Therefore, if the above test results are summed up,
The addition amount of Al ₂ O ₃ is set in the range of 0.001 to 0.4 wt%, yet Al ₂ O ₃ in the case of performing the grinding step
A ball mill containing substantially no components, for example, a zirconia ball mill is used, whereby the electrical resistivity is relatively high, the mechanical strength such as the resistance strength and the electromechanical coupling coefficient can be relatively high, and the piezoelectric ceramic composition It is possible to improve various characteristics of. Therefore, by using this composition, a highly reliable laminated piezoelectric actuator can be provided.

In the above embodiment, Sr was used as the Pb replacement material, but the present invention is not limited to this, and other alkaline earth metals, such as Ba and Ca, will produce the same effect. Obtainable. Further, since Mn, Fe, and Cr are added, not only these oxides but also Mn (OC _{2
H 5) 2, Fe (OC} 2 H 5) 3, Cr (OC 2 H 5)
It is also possible to use ₃ .

[0024]

As described above, according to the present invention, the following excellent operational effects can be exhibited. Al
Is set in the range of 0.001 to 0.04% by weight in terms of Al ₂ O ₃ , and in the pulverizing step, a ball mill that does not substantially contain an Al component is used.
Since the mixture of the l component is prevented, the electrical resistivity, the mechanical strength, and the electromechanical coupling coefficient can be increased, and these characteristics can be improved. Therefore, it is possible to provide a material that is extremely useful as a material for an actuator, particularly a laminated piezoelectric actuator.

[Brief description of drawings]

FIG. 1 is a graph showing the density of a piezoelectric ceramic composition with respect to the amount of Al ₂ O ₃ added.

FIG. 2 is a graph showing the relationship between the added amount of Al ₂ O ₃ and the electrical conductivity.

FIG. 3 is a graph showing the relationship between the added amount (analytical value) of Al ₂ O ₃ and the dielectric constant.

FIG. 4 is a graph showing the relationship between the added amount (analytical value) of Al ₂ O ₃ and the dielectric constant ratio.

FIG. 5 is a graph showing the relationship between the added amount of Al ₂ O ₃ (analytical value) and the electromechanical coupling coefficient.

FIG. 6 is a graph showing the relationship between the added amount of Al ₂ O ₃ and the average crystal grain size.

FIG. 7 is a graph showing the relationship between the amount of Al ₂ O ₃ added and the bending strength.

[Explanation of symbols]

 A Characteristic curve of piezoelectric ceramic composition of the present invention B Characteristic curve of conventional piezoelectric ceramic composition

Claims (3)

[Claims] 1. A piezoelectric ceramic composition having a basic composition represented by the composition formula Pb (Zr _X Ti _1-x ) O ₃ (where 0.52 ≦ X ≦ 0.59), wherein 2-1
2 mol% is substituted with at least one of Ca, Sr and Ba, 0.1 to 2.0 wt% of Sb is converted into Sb ₂ O ₃ , and at least one of Mn, Fe and Cr is an oxide. 0.01 to 0.5% by weight, Al is Al ₂ O
A piezoelectric ceramic composition comprising 0.001 to 0.04% by weight in terms of ₃ , respectively. 2. A method for producing a piezoelectric ceramic composition having a basic composition represented by a composition formula Pb (Zr _X Ti _1-x ) O ₃ (where 0.52 ≦ X ≦ 0.59), A Ca-, Sr- or Ba-containing substance is weighed so that 2 to 12 mol% of Pb atoms are replaced with at least one of Ca, Sr and Ba, and Sb is converted into Sb ₂ O ₃ to give 0.1-2. 0% by weight, 0.01 to 0.5% by weight of at least one of Mn, Fe, and Cr converted to oxides, Al is Al ₂
Each of them was weighed so as to contain 0.001 to 0.04% by weight in terms of O ₃ and mixed with the basic raw material to prepare a mixture, and the mixture was pulverized by a ball mill substantially free of Al. A method for producing a piezoelectric ceramic composition, characterized in that the crushed product is configured to be sintered. 3. The method for producing a piezoelectric ceramic composition according to claim 2, wherein the Al-free ball mill is a zirconia ball mill.