JPH0745883A - Piezoelectric ceramic composition - Google Patents

Abstract

PURPOSE:To provide a piezoelectric ceramic composition which can be baked at low temperatures, for which it is not required to use a special sagger in a baking operation executed to control the atmosphere of Pb and for which it is not required to use a material such as high-cost Pt or the like as an internal electrode when an integrally baked ceramic element such as a piezoelectric actuator is manufactured. CONSTITUTION:In a perovskite-byte piezoelectric ceramic composition whose fundamental composition is XPbb (Nialpha/3Nb2/3)O3-YPbZrO3-ZPbTiO3 and which is expressed by a general symbol of ABO3, X, Y and Z are set within ranges of 0.20<=X<=0.60,, 0.15<=Y<=0.60 and 3.0<=Z<=0.60, the Ni ratio (alpha) of a B-site is et at !<=alpha<=2 so as to be more excessive than a stoichiometric composition, and the Pb ratio (beta) of an A-site is set at 1<=beta<=1.06 so as too be more excessive than a stoichiometric composition.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to piezoelectric ceramics, and more particularly to a piezoelectric ceramic composition having a large piezoelectric d constant suitable for use as a material for piezoelectric actuators and buzzers.

[0002]

Known as large piezoelectric ceramics of the Related Art piezoelectric d _{constant, Pb (Ni 1/3 Nb 2/} 3) O 3 -PbZ
A piezoelectric material having a basic composition of rO ₃ -PbTiO ₃ is usually lead oxide (PbO), zirconium oxide (Zr
O ₂ ), titanium oxide (TiO ₂ ), nickel oxide (Ni
O), niobium pentoxide (Nb ₂ O ₅ ) and other oxide raw materials are mixed so as to have a predetermined stoichiometric composition, mixed and dispersed using a ball mill or the like, and then calcined at a predetermined temperature, Further, it is manufactured by crushing and mixing with a binder, molding into a predetermined shape, and firing at a high temperature of 1200 ° C. or higher to cause a sintering reaction.

[0003]

However, in the above-mentioned conventional manufacturing method, the piezoelectric ceramic composition (ceramics) after calcination is used.
Since the firing temperature is as high as 1200 ° C. or higher, there is a problem that Pb evaporates from the ceramics violently, causing variations in piezoelectricity inside the ceramics.

In addition, when trying to suppress the evaporation of Pb,
At the time of firing, it is necessary to use a pod with a high degree of airtightness, or to use an atmosphere control technique such as putting PbO or the like inside the pod to create an excessive Pb atmosphere.
And as a result, the manufacturing process becomes complicated,
There is a problem in that the quality varies. Further, since the pod is repeatedly used at high temperature, it has a problem that its life is short and the manufacturing cost is increased.

Further, when manufacturing integrally fired ceramics such as piezoelectric actuators, since the firing temperature is high, it is necessary to use a noble metal having a high melting point such as Pt as an internal electrode material. There is a problem that it causes the cost to rise.

The present invention solves the above-mentioned problems, and can be fired at a low temperature, the evaporation of Pb is small, a special pod is used during firing, and the atmosphere of Pb is controlled. It is also an object of the present invention to provide a piezoelectric ceramic composition that does not need to use expensive materials such as Pt as internal electrodes when manufacturing a monolithic firing type ceramic element such as a piezoelectric actuator. To do.

[0007]

[Means for Solving the Problems] To achieve the above object
In addition, the piezoelectric ceramic composition of the present invention is XPbβ (Niα /₃
Nb_2/3) O₃-YPbZrO₃-ZPbTiO₃The basic set
Completion, general symbol ABO₃Perovskite type represented by
Of the piezoelectric ceramic composition, wherein X, Y and Z are each in the range of 0.20 ≦ X ≦ 0.60 0.15 ≦ Y ≦ 0.60 0.30 ≦ Z ≦ 0.60, and , The B site Ni ratio (α) is in the range of 1 <α <2, and is more than the stoichiometric composition.
In addition, the Pb ratio (β) of the A site is in the range of 1 <β ≦ 1.06, which is in excess of the stoichiometric composition.
Characterize.

Further, the specific surface area (SS) of the piezoelectric ceramic material powder before firing is 10 m ² / g or more (SS ≧ 10 m ² / g)
Is characterized by

[0009]

[Function] B site Ni existing in excess of the stoichiometric composition
Although the detailed mechanism by which Pb of A site and Pb of A site enables low temperature sintering is not always clear, it is considered as follows at present.

Lead zirconate titanate containing a large amount of Nb (P
It is well known that the ZT) -based material easily forms a pyrochlore phase (oxide of Pb and Nb) as an intermediate product during firing. Therefore, the piezoelectric ceramic composition of the present invention having the above composition undergoes a process of producing Pb (Ni, Nb) O ₃ from the pyrochlore phase in the firing step.

By the way, since Ni (NiO) in the raw material has a poor dispersibility, Ni (NiO) is contained in the ceramic before firing.
Is excessive, and a portion lacking Ni occurs.

In a system (part) lacking Ni,
Is Pb (Ni, Nb) O from the pyrochlore phase during firing.
₃Reaction does not proceed completely, and part of it is composed of Pb and Nb.
Pyrochlore structure intermediate product (Pb₂Nb₂O
₇) Is likely to remain. Burning this Pyrochlore phase
The binding property is lead zirconate titanate (Pb (Zr, Ti) O
It is equivalent to the sinterability of 3), and if this phase remains, it will be low temperature.
I can't hope to sinter.

On the other hand, in a system (part) in which Ni is excessively present,
Is Pb (Ni, Nb) O from the pyrochlore phase.₃Against
Response progresses completely, Pb₂Nb₂O₇(Pyrochlore structure
It is difficult to remain as an intermediate product of
Of the Chlore phase, Pb₃Nb₂O 8 is Pb (Ni, Nb)
O₃It is a compound that reacts with and has a low melting point of 925 ° C.
Therefore, it becomes a liquid phase for low temperature sintering of PZT ceramics.
It is considered to contribute.

In addition, it is considered that by making the Pb ratio of the A site excessive, the production of this liquid phase is further accelerated and the lowering of the sintering temperature is promoted.

Therefore, as in the piezoelectric ceramic composition of the present invention, Ni in the B site and Pb in the A site are contained in a stoichiometric composition or more, and Ni and P are contained in most of the composition.
By producing a state in which b is present in excess, it becomes possible to sinter at a low temperature.

In the piezoelectric ceramic composition of the present invention, X (that is, the molar ratio of Pb) is 0.20 to 0.60.
The reason is that when X is less than 0.20, the amount of the intermediate product produced is small, so that the contribution to the sinterability is small, and when the amount of X exceeds 0.60, the Curie point (Tc ) Becomes 100 ° C. or lower, and the temperature stability of the resonance frequency and displacement characteristics near room temperature deteriorates.

Further, Y (that is, the molar ratio of PbZrO ₃ ) is set to 0.15 to 0.60 because the piezoelectricity is small when Y is less than 0.15 away from MPB or exceeds 0.60. This is because it cannot be applied to applications such as piezoelectric actuators and buzzers that require high electromechanical coupling coefficient (Kp) and relative permittivity (ε ₃₃ / ε ₀ ).

Z is limited to the range of 0.30 to 0.60 in order to satisfy 1 = X + Y + Z.

Further, the value of α is limited to the range of 1 <α <2 because when the value of α is 1 or less, the formation of the pyrochlore phase is promoted, and the low temperature sinterability cannot be obtained. Further, when the value of α is 2 or more, Ni is solid-dissolved in the grains during firing and the electric characteristics are largely changed, and it becomes impossible to obtain the required characteristics.

Further, the value of β is limited to the range of 1 <β ≦ 1.06 because the effect of improving the low temperature sinterability is not always sufficient when the value of β is 1 or less, and β When the value of exceeds 1.06, excess Pb becomes a glass phase and remains in the sintered body, resulting in a decrease in piezoelectricity, which is not preferable.

Regarding the value of β, it is possible to obtain the effect of low-temperature sintering even if β is excessive alone, without causing a problem with the relationship with α, but the piezoelectricity is greatly reduced. Therefore, it is not preferable to make β alone excessive.

Further, the specific surface area (SS) of the piezoelectric ceramic material powder before firing is 10 m ² / g or more (SS ≧ 10 m ² /
g) further improves low temperature sinterability,
It becomes possible to sinter at a temperature below 900 ° C. It is considered that this is because the particles of the piezoelectric ceramic material powder are finely divided to improve the dispersibility of Ni and Pb.

[0023]

EXAMPLES Examples of the present invention will be shown below to more specifically describe the features thereof.

First, as a starting material, Pb ₃ O ₄ , TiO
₂ , ZrO ₂ , NiO, Nb ₂ O ₅ were prepared, these starting materials were weighed so as to have the compositions shown in Tables 1 and 2, wet-mixed with a ball mill, and then 700-90.
It was calcined at 0 ° C. for 2 hours and pulverized (finely pulverized) to obtain a calcined powder. Then, a vinyl acetate-based binder was added to the calcined powder, and wet mixing was further performed, followed by drying and granulation.
It is shaped into a disc at a pressure of 00 to 2000 kg / cm ² , and it is fired at 850 to 1200 ℃, diameter 10 mm, thickness 1 mm.
I got a porcelain disk.

The surface of the porcelain disc (both main surfaces)
After applying silver paste to the above and baking at 800 ° C for 2 hours to form a silver electrode, 3k in silicon oil at 80 ° C
A DC voltage of V / mm was applied and polarization was performed to obtain a piezoelectric ceramic disc (sample).

The relative permittivity (ε ₃₃ / ε ₀ ), electromechanical coupling coefficient (Kp), and mechanical quality coefficient (Qm) of these samples were measured. The results are shown in Table 1 and Table 2.
Shown in. In Tables 1 and 2, the sample numbers marked with * are samples having compositions outside the scope of the present invention.

[0027]

[Table 1]

[0028]

[Table 2]

As shown in Table 1 and Table 2, the relative permittivity (ε ₃₃ /
It can be seen that, regarding ε ₀ ), the electromechanical coupling coefficient (Kp), and the mechanical quality coefficient (Qm), almost good results are obtained.

Regarding α, sample No. 16 in Table 2
As can be seen from the comparison between (α = 1.0) and sample No. 17 (α = 1.5), when the value of α is 1 or less, the result is that the formation of the pyrochlore phase is promoted, which is sufficient. It can be seen that the low temperature sinterability cannot be obtained. Also, sample No. 2
As shown in 1 (α = 2.5), when the value of α is 2 or more, Ni dissolves into the grains during firing and the electrical characteristics change significantly (that is, Kp decreases and Qm decreases). It becomes unfavorable because it becomes large).

Regarding β, sample No. 12 in Table 1
As can be seen from the comparison between (β = 1.02) and sample No. 13 (β = 0.98), when β becomes 1 or less, the effect obtained by making β larger than 1 is lost, and As can be seen from the comparison between sample Nos. 18 and 20 in Table 2, when the value of β exceeds 1.06, excess Pb becomes a glass phase and remains in the sintered body, resulting in a decrease in piezoelectricity. I understand.

Regarding the value of β, it is possible to obtain the effect of low-temperature sintering even if β is excessive alone, without making the relationship with α a problem. 16
(Α = 1.0, β = 1.02, only β is excessive) and sample No.
As shown in the comparison of 17 (α = 1.5, β = 1.02, both α and β are excessive), when β alone is excessive, the piezoelectricity is significantly decreased, which is preferable. Absent.

Further, in FIG. 1, X = 0.40, Y = 0.2
3, in the composition of Z = 0.38, α = 1.0 and α =
The sinterability in the case of 1.5 (both β = 1.00), that is, the relationship between the firing temperature and the sintered density (density of the sintered body) is shown, and X = 0.40 in FIG. , Y = 0.2
3, in the composition of Z = 0.38, α = 1.0, β =
Sinterability is shown when 1.00 and when α = 1.5 and β = 1.02.

From FIGS. 1 and 2, when the raw material in which both Ni and Pb are excessive (α = 1.5, β = 1.02) is used, the raw material in which only Ni is excessive (α = 1.5, β =
It can be seen that the low temperature sinterability is improved as compared with the case where 1.00) is used.

Furthermore, after calcination, the raw material powder (piezoelectric ceramic material
By finely pulverizing (powder), low temperature sinterability is further improved.
It is possible to increase sample No. 17 (especially by pulverizing
No raw material powder used) and Sample No. 18 (finely pulverized raw material)
Ni and Pb, as seen in comparison with powder)
Is excessive, and the raw material powder finely pulverized after calcination is used
As a result, low firing temperature (below 900 ° C)
Material No. 18 has sufficient piezoelectricity even if fired at 850 ° C.
You can see that you can get it. In this invention, the crushed particle size
The value of specific surface area (SS) was used as an index of
S value is 10m²If it is smaller than / g, it falls below 900 ° C.
To obtain low temperature sinterability that can be fired at such a low temperature
It will be difficult. Therefore, temperatures below 900 ° C
Compatible with low temperature sinterability and piezoelectricity
In order to have a specific surface area of 10 m 2 / g or more
Will be required.

The piezoelectric ceramic composition of the present invention is not limited to the above-mentioned embodiments, and may be applied and modified within the scope of the gist of the invention, such as changing its composition and manufacturing method. It is possible.

[0037]

According to the present invention as described above, the piezoelectric ceramic composition of the present _{invention, XPbβ (Niα / 3 Nb 2/3} ) O 3 -YPbZrO
₃ -ZPbTiO ₃ as a basic composition, the perovskite type represented by the general symbol ABO ₃ of the piezoelectric ceramic composition, X,
Y and Z are set to the above predetermined ranges, the Ni ratio (α) of the B site is set to 1 <α <2, which is in excess of the stoichiometric composition, and the Pb ratio (β) of the A site is set to 1 <β. ≦ 1.0
6 and the stoichiometric composition are excessive, so in particular, without using a chemical synthesis method such as a coprecipitation method or a sol-gel method, a conventional method of mixing oxides is used. It becomes possible to lower the firing temperature considerably as compared with the conventional one while ensuring the required piezoelectricity.

Further, the raw material powder before firing is finely pulverized to have a specific surface area (SS) of 10 m ² / g or more (SS ≧ 10 m ²
/ G) makes it possible to sinter at a lower temperature.

Therefore, according to the piezoelectric ceramic composition of the present invention, as in the case of producing a conventional piezoelectric ceramic composition, a special pod having a high degree of sealing is used at the time of firing, or P
Since it is not necessary to control the atmosphere of b and the firing temperature is lowered, the life of the pod can be significantly improved. Further, even in the case of manufacturing the integrally fired piezoelectric actuator, since it is not necessary to use a high melting point noble metal such as Pt as the internal electrode, it is possible to use a relatively inexpensive Ag—Pd alloy or the like. Manufacturing costs can be significantly reduced.

[Brief description of drawings]

FIG. 1 is a composition in which X = 0.40, Y = 0.23, = 0.38, α = 1.0 and α = 1.5 (both β =
It is a diagram showing sinterability in the case of (1.00).

FIG. 2 shows the case where α = 1.0 and β = 1.00 in the composition of X = 0.40, Y = 0.23, = 0.38, and
FIG. 3 is a diagram showing sinterability when α = 1.5 and β = 1.02.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI technical display location C04B 35/49 Z

Claims (2)

[Claims] 1. A _{XPbβ (Niα / 3 Nb 2/3)} O 3 -YP
The basic composition is bZrO ₃ —ZPbTiO ₃ and the general symbol A
A perovskite type piezoelectric ceramic composition represented by BO ₃ , wherein X, Y and Z are respectively 0.20 ≦ X ≦ 0.60 0.15 ≦ Y ≦ 0.60 0.30 ≦ Z ≦ 0. And the Ni ratio (α) of the B site is in the range of 1 <α <2, which is in excess of the stoichiometric composition, and the Pb ratio (β) of the A site is , 1 <β ≦ 1.06, which is in excess of stoichiometric composition. 2. The piezoelectric ceramic composition according to claim 1, wherein the specific surface area (SS) of the piezoelectric ceramic material powder before firing is 10 m ² / g or more (SS ≧ 10 m ² / g).