JPH11240759A - Piezoelectric porcelain for actuator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-lead metal-based piezoelectric porcelain having a high Curie temperature of >=150 deg.C and a piezoelectric strain constant (d33 ) in a practical use level of >=80 pC/N. SOLUTION: This piezoelectric porcelain consists mainly of crystal particles comprising a tungsten bronze type compound oxide expressed by the formula: Sr2 NaNb5 O15 in which a part of Nb is substituted by V and/or Ta. Therein, part of Sr is preferably replaced by at least one or more kinds of elements selected from Mg, Ca and Ba, and part of Na is desirably replaced by K. The piezoelectric porcelain is especially expressed by the atomic ratio composition formula: (Sr2-a Aa )x (Na1-b Kb )y (Nb5-c Vc )O15 [0.10<=(a)<=0.65; 0.20<=(b)<=0.80; 0<(c)<=0.10; 0.96<=(x)<=1.04; 0.80<=(y)<=1.20; A is at least one kind of Mg, Ca and Ba].

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic for an actuator, and more particularly, to positioning and positioning in a precision machine tool.
The present invention relates to a piezoelectric ceramic for an actuator used for an optical path length control and a flow control valve of an optical device, an ultrasonic motor, or a brake device of an automobile.

[0002]

2. Description of the Related Art An actuator using a piezoelectric material uses a strain and a force generated through a piezoelectric phenomenon as a mechanical driving source, and is a valve for positioning in a precision machine tool, controlling an optical path length of an optical device, and controlling a flow rate. Applications have been developed for ultrasonic motors, automobile brake devices, and the like. As a piezoelectric material used for an actuator, lead zirconate titanate (PZT) has been most widely used because of its excellent piezoelectricity. However, recently, when lead-based waste is exposed to acid rain or the like, lead is eluted and adversely affects the environment. Therefore, a lead-free piezoelectric material that can be used as a substitute for PZT that contains lead at about 60% of its own weight is used. Materials are needed.

As a piezoelectric material for a lead-free actuator, use of a BaTiO ₃ -based porcelain composition is considered. For example, JP-A-2-15979 and JP-A-2-29430 propose to use a BaTiO ₃ -based piezoelectric ceramic composition. BaTiO ₃
The porcelain composition is characterized by having a high relative dielectric constant (ε _33T / ε ₀ ) and a high electromechanical coupling coefficient (k ₃₃ ).
Since it has a large piezoelectric strain constant (d ₃₃ ) of around pC / N, it can be used as a piezoelectric material for a laminated actuator.

On the other hand, Ferroelectrics, 1994, Vol. 160, P265
_{The, Sr 2-x Ca x NaNb} 5 O 15 dielectric constant of the tungsten bronze-type single crystal represented by (ε _33T / ε _0),
It describes the piezoelectric strain constant (d ₃₃ ) and the Curie temperature (T _c ). According to this document, in the single crystal,
The relative permittivity (ε _33T / ε ₀ ) is 1700, the piezoelectric strain constant (d ₃₃ ) is 270 pC / N, and the Curie temperature (T _c ) is 2
Since it has a characteristic of 70 ° C., it is excellent for actuators.

[0005]

However, Japanese Patent Application Laid-Open Nos. 2-159079 and 2-2943 described above.
In the BaTiO ₃ -based porcelain composition disclosed in Japanese Patent Publication No. 0-300, a large piezoelectric strain constant (d ₃₃ ) of about 300 pC / N is used.
However, since the Curie temperature (T _c ) of BaTiO ₃ itself is as low as about 120 ° C. and the Curie temperature cannot be reduced to obtain a larger piezoelectric strain constant (d ₃₃ ), it is used as a piezoelectric material. The upper limit of the usable operating temperature is about 100 ° C. at the highest, and there is a problem that it cannot be used in a temperature environment exceeding this.

On the other hand, the present inventors have prepared a piezoelectric ceramic with the same composition as the tungsten bronze type single crystal represented by Sr _2-x Ca _x NaNb ₅ O ₁₅ described in the above-mentioned document, The dielectric constant (ε _33T / ε ₀ ) and the Curie temperature (T _c ) of the piezoelectric element are almost the same as those of the single crystal, but the piezoelectric strain constant (d ₃₃ ) is as low as 50 to 60 pC / N. It is not at a level that can be used as a piezoelectric ceramic.

The present invention relates to a compound represented by the general formula: Sr ₂ NaNb ₅ O ₁₅
In the tungsten bronze type composite oxide represented by the formula, the Curie temperature is as high as 150 ° C. or higher, and 80 pC / N
And to provide a lead-free piezoelectric porcelain having a more practical level piezoelectric strain constant of (d _33).

[0008]

A piezoelectric ceramic for an actuator according to the present invention comprises a tungsten bronze type composite oxide represented by the general formula: Sr ₂ NaNb ₅ O ₁₅ , and comprises Nb
Is mainly composed of crystal grains in which a part of is replaced by V and / or Ta. Here, part of Sr is Mg, Ca
And Ba are desirably substituted, and a part of Na is desirably substituted with K.

The piezoelectric ceramic for an actuator according to the present invention has a composition formula of (Sr _2-a A _a ) _x (Na
_1-b K _b ) _y (Nb _{5 -c} V _c ) O ₁₅ , wherein a, b, c, x and y are 0.10 ≦ a ≦ 0.65;
0.20 ≦ b ≦ 0.80, 0 <c ≦ 0.10, 0.96
It is desirable to satisfy ≦ x ≦ 1.04 and 0.80 ≦ y ≦ 1.20. Here, A is at least one of Mg, Ca and Ba.

The composition formula based on the atomic ratio is represented by (Sr _2-a
When expressed as _{A a) x (Na 1-} b K b) y (Nb 5-c Ta c) O 15, wherein a, b, c, x and y are 0.10
≦ a ≦ 0.65, 0.20 ≦ b ≦ 0.80, 0 <c ≦
0.50, 0.96 ≦ x ≦ 1.04, 0.80 ≦ y ≦
It is desirable to satisfy 1.20. Where A is M
At least one of g, Ca and Ba.

The piezoelectric ceramic for an actuator according to the present invention is characterized in that C
It is desirable that u and / or Mn be contained in a total of 0.1 to 1.5 parts by weight in terms of CuO and MnO ₂ .

[0012]

The piezoelectric ceramic for an actuator according to the present invention is made of a tungsten bronze type composite oxide represented by the general formula: Sr ₂ NaNb ₅ O ₁₅ , wherein crystal grains in which a part of Nb is substituted by V and / or Ta are used. Because it is mainly used, the Curie temperature (T _c ) can be increased to 150 ° C. or more,
The dielectric constant (ε _33T / ε ₀ ) and / or the electromechanical coupling coefficient (k ₃₃ ) are improved to increase the piezoelectric strain constant (d ₃₃ ) to 80.
It can be improved to a practical level of pC / N or more.

Further, the piezoelectric ceramic for an actuator according to the present invention does not contain lead, which has a bad influence on the environment, and does not contain volatile components such as bismuth, so that it can be fired in the air and is therefore easy to manufacture.

Further, part of Sr in the above general formula is Mg,
By substituting at least one of Ca and Ba and partially substituting Na with K, the Curie temperature (T _c ) can be increased and the relative dielectric constant (ε
_33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) can be improved to further increase the piezoelectric distortion constant (d ₃₃ ).

Further, Cu and / or Mn are replaced with C
By containing a predetermined amount in terms of uO and MnO ₂ , the firing temperature can be lowered without substantially lowering the piezoelectric properties of the porcelain, and the production cost of the porcelain can be reduced.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION A piezoelectric ceramic for an actuator according to the present invention comprises a tungsten bronze type composite oxide represented by the general formula: Sr ₂ NaNb ₅ O ₁₅ , and a part of Nb is V
And / or crystal particles substituted with Ta. Thus, the conventionally known Sr ₂ NaNb
By substituting a part of Nb of ₅ O ₁₅ with V and Ta, the relative dielectric constant (ε _33T / ε ₀ ) and / or the electromechanical coupling coefficient (k ₃₃ ) are improved, and the piezoelectric strain constant (d ₃₃ ) can be higher.

Further, a part of Sr is made of Mg, Ca and Ba.
It is desirable to substitute at least one of them and to partially replace Na with K. By such substitution, the Curie temperature (T _c ) can be increased, and the relative dielectric constant (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) can be further improved.

In the piezoelectric ceramic for an actuator according to the present invention,
In particular, the composition formula based on the atomic ratio is expressed as (Sr _2-a A _a ) _x (Na
_1-b K _b ) _y (Nb _5-c B _c ) O ₁₅ , wherein a, b, c, x and y are 0.10 ≦ a ≦ 0.65;
0.20 ≦ b ≦ 0.80, 0.96 ≦ x ≦ 1.04,
0.80 ≦ y ≦ 1.20, 0 when B is V
<C ≦ 0.10, 0 <c ≦ 0.50 when B is Ta
It is desirable to satisfy Here, A is at least one or more of Mg, Ca and Ba.

Here, the reason why a is set in the range of 0.10 ≦ a ≦ 0.65 is that when a is less than 0.10, the relative dielectric constant (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃₎
This is because when a is larger than 0.65, the relative dielectric constant (ε _33T / ε ₀ ) is significantly reduced. A is preferably 0.20 ≦ a ≦ 0.50 from the viewpoint that the dielectric constant (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) are excellent.

In the above-mentioned main components, the reason why b representing the ratio of Na and K is in the range of 0.20 ≦ b ≦ 0.80 is as follows.
In this range, the Curie temperature (T _c ) is high, the relative dielectric constant (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) are high.
This is because a porcelain having the following formula can be obtained. That is,
If b is smaller than 0.20, the electromechanical coupling coefficient (k ₃₃ ) decreases, and if b is larger than 0.80, the Curie temperature (T _c ) decreases. b is, in particular,
From the viewpoint that the electromechanical coupling coefficient (k ₃₃ ) is excellent, it is desirable that b is 0.50 ≦ b ≦ 0.80.

In the above-mentioned main component, a part of Nb is replaced by a specific metal element B (V and / or Ta) by c. When V is replaced by V, c is 0 <c ≦ 0. 1
When substituting with 0 and Ta, 0 <c ≦ 0.50 is satisfied.

When a part of Nb is replaced by V, sinterability is deteriorated if it is replaced too much. Therefore, c is desirably 0.10 or less. On the other hand, when a part of Nb is replaced with Ta, the Curie temperature (T _c ) decreases as the replacement amount increases. Therefore, c is preferably 0.50 or less. In particular, since a Curie temperature (T _c ) is high and the piezoelectric strain constant (d ₃₃ ) is excellent, the range of c when a part of Nb is replaced with V is 0.02 <c ≦ 0.05.
Is desirable, and when replacing with Ta, 0.0
It is particularly desirable that 5 ≦ c ≦ 0.30. In addition, Nb
May be replaced with V and Ta, but in this case, it is desirable that c be 0 <c ≦ 0.10.

Further, x in the above main component is 0.96.
The reason for the range of ≦ x ≦ 1.04 is that when x is less than 0.96, a different phase is likely to occur in the porcelain, the piezoelectric strain constant (d ₃₃ ) is reduced, and the value is larger than 1.04. This is because the sinterability of the porcelain deteriorates and the piezoelectric distortion constant (d ₃₃ ) decreases.

The reason for setting y to be in the range of 0.80 ≦ y ≦ 1.20 is that when y is less than 0.80, the relative dielectric constant (ε
_33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) decrease, and when y is larger than 1.20, the sinterability of the porcelain deteriorates, and the electromechanical coupling coefficient (k ₃₃ ) becomes remarkable. It is because it falls. From the viewpoint that the porcelain has good sinterability and a large piezoelectric strain constant (d ₃₃ ), x is 0.98 ≦ x ≦ 1.
02 and y are preferably in the range of 0.90 ≦ y ≦ 1.10.

Further, in the present invention, the composition formula based on the atomic ratio is expressed as (Sr _2-a A _a ) _x (Na _{1 -b} K _b ) _y (Nb _5-c B
_c ) With respect to 100 parts by weight of the main component composed of O ₁₅ , Cu and / or Mn are 0.1 to 0.1% in total in terms of CuO and MnO _2.
It is desirable to contain 1.5 parts by weight, because this lowers the firing temperature and facilitates the production of porcelain.
The reason that the total range of the added amounts of Cu and Mn is 0.1 to 1.5 parts by weight is that when the added amount is less than 0.1 part by weight, the effect of addition is hardly recognized, If the number is larger than the number of parts, a different phase is likely to occur in the porcelain, and the piezoelectricity of the porcelain is significantly reduced. In particular, low firing temperature of the porcelain, terms indicating a large piezoelectric strain constant (d _33), the addition amount of Cu and / or Mn total 0.4
Desirably, it is 1.0 part by weight.

The piezoelectric ceramic for an actuator according to the present invention has a general formula: (Sr _2-a A _a ) _x (Na _{1 -b} K _b )
_The main crystal phase is a tungsten bronze-type crystal phase represented by _y (Nb _5-c B _c ) O _{15. When} Cu and / or Mn is contained, most of these metal elements are as described above. Although it is a crystal phase dissolved in the main crystal phase, it may be partially present at the grain boundary of the main crystal phase.

In the piezoelectric ceramic for an actuator of the present invention,
Inevitable impurities such as Rb, Ce, Fe, Al, and Si may be mixed. Also, from the press molding die, etc., N
Metal elements such as i, Cr, Mo, and Ni may be mixed. Further, in order to improve temperature characteristics and heat resistance, L
i, Cr, Co, etc. may be added.

The piezoelectric ceramic for an actuator of the present invention can be manufactured, for example, as follows. First, S
_{rCO 3, MgCO 3, CaCO 3} , BaCO 3, Na
₂ CO ₃ , K ₂ CO ₃ , Nb ₂ O ₅ , V ₂ O ₅ , Ta ₂
O ₅ , CuO and MnO ₂ powders are mixed at a predetermined ratio, calcined at 900 to 1100 ° C. for 2 to 5 hours, and then pulverized to obtain a powder of a piezoelectric material having a desired composition.

An organic binder is mixed with the powder, molded into a desired shape by a die press, an isostatic press or the like, and then fired at 1100 to 1300 ° C. for 2 to 5 hours to obtain a porcelain. This is processed to a desired thickness as needed and used.

The same result can be obtained by adding CuO and / or MnO ₂ not only at the time of preparation but also after calcining and before pulverization. In this case, however, the total amount of CuO and MnO ₂ is 1 part by weight or less. Is desirably added. If the addition amount is larger than this, a remarkably different phase easily occurs in the porcelain, and the piezoelectric characteristics of the porcelain deteriorate.

Further, Cu and / or Mn is CuO,
Although it contains a predetermined amount in terms of MnO ₂ , it may be not only CuO and / or MnO ₂ powder but also other compound powder containing Cu and / or Mn. Further, SrCO ₃ , MgCO ₃ , CaCO ₃ , BaCO
₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Nb ₂ O ₅ , V
₂ O ₅ , Ta ₂ O ₅ , CuO and MnO ₂ powders can be prepared by firing any of compounds containing respective metal elements, such as oxides, carbonates and acetates, or compounds such as organic metals. There is no problem as long as it becomes an oxide.

[0032]

EXAMPLES As starting materials, SrCO ₃ , MgCO ₃ ,
CaCO ₃ , BaCO ₃ , Na ₂ CO ₃ , K ₂ CO ₃ ,
Nb ₂ O ₅ , V ₂ O ₅ , Ta ₂ O ₅ , CuO and Mn
Using the O ₂ powder, the composition of the sintered body is determined by the composition formula based on the molar ratio: (Sr _2-a A _a ) _x (Na _{1 -b} K _b ) _y (Nb _5-c
B _c ) Weigh so that a, b, c, x and y in O ₁₅ have the values shown in Table 1, and further, sample No. 30 in Table 1.
CuO in an amount shown in Table 2 with respect to 100 parts by weight of the main component
And / or MnO ₂ powder was added. This mixture was wet-mixed in a ball mill using ZrO ₂ balls for 12 hours.

Next, after drying this mixture, it was calcined in the air at 1000 ° C. for 3 hours, and the calcined product was pulverized again by the above-mentioned ball mill. Thereafter, a binder (PVA) was mixed with the pulverized material to granulate. The resulting powder is 1.5
It was press-molded into a cylinder having a diameter of 5 mm and a thickness of 8 mm at a pressure of t / cm ² .

These compacts were arranged on a plate made of MgO.
At 5 ° C. for 5 hours.
Fired for hours. The obtained porcelain was measured for its X-ray diffraction pattern and analyzed for peaks. The sample of the present invention was composed of a tungsten bronze-type composite oxide represented by Sr ₂ NaNb ₅ O ₁₅ , It was confirmed that the main component was a crystal particle whose part was substituted with V and / or Ta.

A silver electrode is baked on the piezoelectric ceramic thus obtained.
Polarization was performed by applying a DC electric field of 8 kV / mm in silicon oil at 50 ° C.

Then, the relative dielectric constant (ε _33T / ε ₀ ) and the longitudinal resonance / anti-resonance frequency were measured at room temperature using an impedance analyzer, and the electromechanical coupling coefficient (k ₃₃ ) and the elastic compliance (S _33E ) were measured. ) Was calculated to determine the piezoelectric strain constant (d ₃₃ ) of the porcelain.

Further, by plotting the relative dielectric constant of the piezoelectric ceramic as a function of temperature, the temperature at the phase transition point between the ferroelectric phase and the paraelectric phase (Curie temperature (T _c )) was determined. These results are shown in Tables 1 and 2.

[0038]

[Table 1]

[0039]

[Table 2]

From these Tables 1 and 2, all of the samples of the present invention have a high Curie temperature of 150 ° C. or more, can be used even at a temperature of 100 ° C., and have a piezoelectric strain constant ( d ₃₃₎ is 80 pC / N or more, and particularly it can be seen that the 100 pC / N or more.

On the other hand, it can be seen that the piezoelectric strain constant (d ₃₃ ) is low in the sample No. 17 of the comparative example in which a part of Nb is not replaced with V or Ta. In addition, Sr _{2 of} the composition formula Sr ₂ NaNb ₅ O ₁₅
It can be seen that in the conventional composition in which a part of was replaced by Ca, the piezoelectric strain constant (d ₃₃ ) was as low as 59 pC / N (No. 1).
8).

Also, when the substitution amount a of Sr with Mg, Ca, and Ba is between 0.10 and 0.65, it has a peak of the piezoelectric strain constant (d ₃₃ ) (Sample Nos. 1 to 5), K
It can be seen that the piezoelectric strain constant (d ₃₃ ) gradually increases when the amount of substitution b due to is increased from 0.2 to 0.8, but the Curie temperature (T _c ) decreases (sample Nos. 6 to 6).
8).

Further, the replacement amount c of Nb by V is 0.0
A peak of the piezoelectric strain constant (d ₃₃₎ between 2 to 0.10, the Curie temperature (T _c) it can be seen that gradually increases (sample No.19~22). In addition, the substitution amount c of Ta for Nb is in the range of 0.05 to 0.50, and the piezoelectric strain constant (d ₃₃ )
Gradually increase, but the Curie temperature (T _c ) gradually decreases (Sample Nos. 23 to 26).

Also, it can be seen that a peak of the piezoelectric strain constant (d ₃₃ ) exists when x is between 0.96 and 1.04, and that the Curie temperature (T _c ) gradually increases (sample Nos. 9 through 9). 1
2). When y is between 0.80 and 1.20, the piezoelectric strain constant (d
₃₃ ), and the Curie temperature ( _Tc ) gradually increases (Sample Nos. 13 to 16).

Further, it can be seen that as the content of CuO and MnO ₂ increases, the firing temperature can be lowered without substantially deteriorating characteristics such as the piezoelectric distortion constant (d ₃₃ ) (Sample No.
32 to 41). It can also be seen that it is desirable to add CuO and MnO ₂ at the same time in order to lower the sintering temperature without deteriorating the piezoelectric characteristics (Sample Nos. 32 to 34).
And 36).

On the other hand, it can be seen that when the added amount of CuO and MnO ₂ exceeds 1.5 parts by weight in total, the piezoelectric strain constant (d ₃₃ ) decreases (Sample No. 41).

[0047]

As described above, according to the piezoelectric ceramic for an actuator of the present invention, the Curie temperature (T _c ) is 15
A piezoelectric strain constant (d higher than 0 ° C. and 80 pC / N or more)
₃₃ ), and a lead-free piezoelectric material that can be practically used as a piezoelectric material for a multilayer actuator can be provided. Since it does not contain lead, it is a piezoelectric material that has no fear of adversely affecting the environment due to elution of lead by acid rain.
Further, the piezoelectric ceramic according to the present invention can be easily fired and can be fired at a low temperature, so that the manufacturing cost can be reduced.

Claims (5)

[Claims] 1. A tungsten bronze type composite oxide represented by the general formula: Sr ₂ NaNb ₅ O ₁₅ , characterized by being mainly composed of crystal grains in which a part of Nb is substituted by V and / or Ta. Piezoelectric ceramic for actuator. 2. Part of Sr is replaced by at least one of Mg, Ca and Ba, and part of Na is K
2. The piezoelectric ceramic for an actuator according to claim 1, wherein said piezoelectric ceramic is replaced by: 3. The composition formula based on the atomic ratio is _expressed as (Sr _2-a A _a ) _x (Na _{1 -b} K _b ) _y (Nb
_5-c V _c ) When expressed as O ₁₅ , the a, b, c, x and y are 0.10 ≦ a ≦ 0.65 0.20 ≦ b ≦ 0.80 0 <c ≦ 0.100 .96 ≦ x ≦ 1.04 0.80 ≦ y ≦ 1.20 A. At least one of Mg, Ca and Ba is satisfied. . 4. A composition formula based on an atomic ratio is represented by (Sr _2-a A _a ) _x (Na _{1 -b} K _b ) _y (Nb _5-c Ta
_c ) When expressed as O ₁₅ , the a, b, c, x and y are 0.10 ≦ a ≦ 0.65 0.20 ≦ b ≦ 0.80 0 <c ≦ 0.50 0.96 ≦ x ≦ 1.04 0.80 ≦ y ≦ 1.20 A ... At least one of Mg, Ca and Ba is satisfied, and the piezoelectric ceramic for actuators according to claim 1 or 2, is satisfied. 5. A method according to claim 3, wherein Cu and / or Mn is replaced by CuO, Mn with respect to 100 parts by weight of the main component.
Piezoelectric ceramic actuator, characterized in that O ₂ containing total 0.1 to 1.5 parts by weight basis.