JPH11278932A - Piezoelectric porcelain - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain non-lead-based piezoelectric porcelain having at least >=100 deg.C high upper limit of temperature used and piezoelectric strain constant (d33 ) in practical level of >=100 pC/N. SOLUTION: This piezoelectric porcelain consists mainly of crystal particles comprising tungsten-bronze type compound oxide represented by the formula; Sr2 NaNb5 O15 and substituting a part of Sr with at least one kind of (Bi1/2 Li1/2 ), (Bi1/2 Na1/2 ) and (Bi1/2 K1/2 ) and at least one kind of element among Mg, Ca and Ba. In the porcelain, it is desirable that a part or all of Na is substituted with K and a part of Nb is substituted with V and/or Ta.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[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 drive source.
Applications to optical path length control of optical devices, flow control valves, ultrasonic motors, automobile brake devices, and the like have been developed. As the piezoelectric material used for the actuator,
Lead zirconate titanate (P
ZT) has been most widely used. However, recently, when lead-based waste is exposed to acid rain or the like, lead is eluted, which has a problem of adversely affecting the environment. Therefore, it can be used as a substitute for PZT containing lead at about 60% of its own weight. There is a need for a piezoelectric material that does not contain lead. As a lead-free piezoelectric material, use of a BaTiO ₃ ceramic composition is conceivable. For example, JP-A-2-15979 and JP-A-2-29430 propose to use a BaTiO ₃ -based piezoelectric ceramic composition. Ba
The TiO ₃ -based porcelain composition is characterized by high relative dielectric constant (ε _33T / ε ₀ ) and high electromechanical coupling coefficient (k ₃₃ ), and has a large piezoelectric strain constant (d ₃₃ ) of about 300 pC / N.
Thus, it can be used as a piezoelectric material for a lead-free actuator.

On the other hand, Ferroelectrics, 19
94, Vol160, the p265 is, Sr _2-x Ca _x NaNb
_{It describes} the relative dielectric constant (ε _33T / ε ₀ ), piezoelectric strain constant (d ₃₃ ), and Curie temperature (Tc) of a single crystal of a tungsten bronze composite oxide represented by ₅ O ₁₅ . According to this document, in the single crystal, the relative dielectric constant (ε
_33T / ε ₀ ) is 1700 and the piezoelectric distortion constant (d ₃₃ ) is 2
It has a characteristic that the Curie temperature (Tc) is 270 ° C. at 70 pC / N.

[0004]

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.
Although a ceramic composition having a large piezoelectric strain constant (d ₃₃ ) of about 0 pC / N can be obtained, the Curie temperature (Tc) of BaTiO ₃ itself is as low as about 120 ° C., and a large piezoelectric strain constant (d ₃₃ ) is obtained. To obtain the Curie temperature (T
There is a problem that the reduction of c) is inevitable, and the upper limit of the operating temperature is lower than 100 ° C.

On the other hand, the present inventors have prepared a piezoelectric ceramic having 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, and The dielectric constant (ε _33T / ε ₀ ) and the Curie temperature (Tc) of the _sample are almost the same as those of the single crystal, but the piezoelectric strain constant (d ₃₃ ) is 50 to 60 pC / N.
It was found that this was not at a level usable as a piezoelectric material for an actuator.

According to the present invention, the upper limit of the operating temperature is at least one.
An object of the present invention is to provide a lead-free piezoelectric ceramic having a high piezoelectric strain constant (d ₃₃ ) of as high as 50 ° C. or more and a practical level of 100 pC / N or more.

[0007]

The piezoelectric ceramic 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 , and a part of Sr is (Bi)
_1/2 Li _1/2 ), (Bi _1/2 Na _1/2 ) and (Bi
_1/2 K _1/2 ) and crystal grains substituted by at least one of Mg, Ca and Ba.

Here, it is desirable that part or all of Na is substituted with K and part of Nb is substituted with V and / or Ta.

[0009] The piezoelectric ceramic of the present invention, the composition formula by atomic ratio _{(Sr 2- (a + b)} A a B b) x (Na 1-c K c) y (Nb
_5-d C _d ) O ₁₅ , wherein a, b, c, d, x and y are
0.10 ≦ a ≦ 0.65, 0 <b ≦ 0.40, 0 ≦ c ≦
1.0, 0 ≦ d ≦ 0.10 when C is V, 0 when C is Ta
≦ d ≦ 0.50, 0.96 ≦ x ≦ 1.04, 0.80 ≦
It is desirable to satisfy y ≦ 1.20. Where A
Is at least one of Mg, Ca and Ba, and B is (Bi _1/2 Li _1/2 ), (Bi _1/2 N
a _1/2) and at least one of (Bi _1/2 K _1/2)
Indicates the species.

[0010]

The piezoelectric ceramic of the present invention has a general formula: Sr ₂ NaNb
_It is composed of a tungsten bronze-type composite oxide represented by ₅ O ₁₅ , and a part of Sr is (Bi _1/2 Li _1/2 ), (Bi
_1/2 Na _1/2 ) and (Bi _1/2 K _1/2 ) and at least one of Mg, Ca and Ba replaced by crystal grains, so that the Curie temperature (Tc ) Is as high as 150 ° C. or higher, and the piezoelectric strain constant (d ₃₃ )
Can be improved to a practical level of 100 pC / N or more.

Further, the piezoelectric ceramic of the present invention does not contain lead, which has an adverse effect on the environment, and can be fired in the air, so that it is easy to manufacture.

Further, by substituting a part or all of Na with K and substituting a part of Nb with V and / or Ta, 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 ).

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric ceramic of the present invention has a general formula: S
A tungsten bronze composite oxide represented by r ₂ NaNb ₅ O ₁₅ , wherein a part of Sr is (Bi _1/2 Li
_1/2 ), (Bi _1/2 Na _1/2 ) and (Bi
_1/2 K _1/2 ) and crystal grains substituted with at least one of Mg, Ca and Ba.

Thus, the conventionally known Sr ₂ NaN
Part of b ₅ O ₁₅ is (Bi _1/2 Li _1/2 ), (Bi _1/2 N
a _1/2 ) and (Bi _1/2 K _1/2 ) and at least one of Mg, Ca and Ba, _{thereby obtaining} a relative dielectric constant (ε _33T / ε ₀ ) and an electromechanical coupling coefficient (k). ₃₃ ) can be higher. In addition, it is desirable to partially or entirely replace Na with K and partially replace Nb with V and / or Ta. By such substitution, the relative dielectric constant (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) are improved, and the piezoelectric strain constant (d ₃₃ ) can be further increased.

In the piezoelectric ceramic of the present invention, in particular, the composition formula based on the atomic ratio is represented by (Sr _{2− (a + b)} A _a B _b ) _x (Na
_{1-cK c} ) _y (Nb _5-d C _d ) O ₁₅ , a, b, c, d, x and y are 0.10 ≦ a ≦ 0.6
5, 0 <b ≦ 0.40, 0 ≦ c ≦ 1.00.96 ≦ x ≦
1.04, 0.80 ≦ y ≦ 1.20, 0 ≦ d ≦ 0.10 when C is V, and 0 ≦ d when C is Ta
It is desirable to satisfy ≦ 0.50. Where A is M
g, at least one of Ca and Ba, and B is at least one of (Bi1 _/ 2Li1 _{/ 2} ), (Bi1 _/ 2Na1 _{/ 2} ) and (Bi1 _/ 2K1 _{/ 2} ). One kind.

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 ) decreases. Relative permittivity (ε
_A is preferably 0.20 ≦ a ≦ 0.50 from the viewpoint of excellent _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ).

In the above main component, b is 0 <b ≦ 0.4.
The reason for _setting the range to 0 is that in this range, it is possible to obtain a porcelain having a high Curie temperature (Tc) and a high relative dielectric constant (ε _33T / ε ₀ ) and an electromechanical coupling coefficient (k ₃₃ ). . As b increases, the Curie temperature (Tc) decreases, but the relative permittivity (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) are significantly improved. In particular, b is 0 <b ≦ 0.30 in that it has a high Curie temperature (Tc) and is excellent in relative permittivity (ε _33T / ε ₀ ) and electromechanical coupling coefficient (k ₃₃ ).
It is desirable that

In the above general formula, when a part of Na is replaced with K, the Curie temperature (Tc) decreases, but the relative dielectric constant (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) increase. There is an effect of doing. Na and K have high Curie temperature (Tc) and are excellent in relative dielectric constant (ε _33T / ε ₀ ) and electromechanical coupling coefficient (k ₃₃ ).
Is preferably in the range of 0.5 ≦ c ≦ 0.80.

Further, in the above general formula, a part of Nb is replaced with a specific metal element C (at least one of V and Ta).
Substituting with (seed) can further improve the piezoelectric distortion constant (d ₃₃ ). When a part of Nb is replaced by V, the Curie temperature (Tc) and the electromechanical coupling coefficient (k
₃₃ ) has the effect of improving. However, excessive substitution with V causes deterioration of the sinterability, so that d is 0 ≦ d ≦
It is desirable to be in the range of 0.10. On the other hand, when a part of Nb is replaced with Ta, the Curie temperature (Tc) decreases, but the relative permittivity (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) improve. Is recognized.
Curie temperature (Tc) is high and relative dielectric constant (ε _33T /
From the viewpoint of excellent ε ₀ ) and electromechanical coupling coefficient (k ₃₃ ), d is desirably 0.50 or less when substituted with Ta. In particular, the Curie temperature (Tc) is higher, in terms of showing the large piezoelectric strain constant (d _33),
When a part of Nb is replaced by V, the range of d is 0.02 ≦
It is preferable that d ≦ 0.04, and the range of d when Ta is substituted is 0.20 ≦ d ≦ 0.40.

Further, x in the above main component is 0.96.
The reason for ≦ 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 ) decreases, and when x is greater than 1.04, This is because the sinterability of the porcelain deteriorates, and the piezoelectric distortion constant (d ₃₃ ) decreases. On the other hand, y is set to 0.80 ≦ y ≦ 1.20
The reason is that when y is less than 0.80, both the relative dielectric constant (ε _33T / ε ₀ ) and the electromechanical coupling coefficient (k ₃₃ ) decrease, and y is larger than 1.20. If it is large, the sinterability of the porcelain deteriorates, and mainly the electromechanical coupling coefficient (k ₃₃ ) decreases. X is 0.98 ≦ x ≦ 1.02, and y is 0.90 ≦ y ≦ 1.10, since the porcelain has good sintering and exhibits a large piezoelectric strain constant (d ₃₃ ).
Is particularly desirable.

The piezoelectric ceramic of the present invention has a general formula: (S
_{r 2- (a + b) A} a B b) x (Na 1-c K c) y (Nb 5-d
C _d ) A tungsten bronze-type crystal phase represented by O ₁₅ is used as a main crystal phase, and most of the metal elements are in a solid solution with the main crystal phase. In the piezoelectric ceramic of the present invention, inevitable impurities such as Rb, Ce, Fe, Al, and Si may be mixed. Also, from press molding dies, etc.,
In some cases, metal elements such as Ni, Cr, Mo, and Ni are mixed. Furthermore, in order to improve temperature characteristics and heat resistance, C
u, Mn, Cr, Co, etc. may be added.

The piezoelectric ceramic of the present invention can be manufactured, for example, as follows. First, SrCO ₃ , MgC
O ₃ , CaCO ₃ , BaCO ₃ , Bi ₂ O ₃ , Li ₂ C
O ₃ , Na ₂ CO ₃ , K ₂ CO ₃ , Nb ₂ O ₅ , V ₂ O
₅ , each powder of Ta ₂ O ₅ is mixed at a predetermined ratio and 900
After calcining at １1100 ° C. for 2 to 5 hours, the resultant is crushed to obtain a piezoelectric material powder 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 1200 to 1280 ° C. for 2 to 5 hours to obtain a porcelain. This is processed to a desired thickness as needed and used.

Note that SrCO ₃ , MgCO ₃ , CaCO
₃ , BaCO ₃ , Bi ₂ O ₃ , Li ₂ CO ₃ , Na ₂ C
O ₃ , K ₂ CO ₃ , Nb ₂ O ₅ , V ₂ O ₅ , Ta ₂ O ₅
The powder may be any of oxides, carbonates, acetates, and other compounds containing the respective metal elements, or compounds of organic metals and the like, as long as they become oxides by firing.

[0024]

EXAMPLES As starting materials, SrCO ₃ , MgCO ₃ ,
CaCO ₃ , BaCO ₃ , Bi ₂ O ₃ , Na ₂ CO ₃ ,
Using K ₂ CO ₃ , Nb ₂ O ₅ , V ₂ O ₅ , Ta ₂ O ₅ , and powder, the composition of the sintered body is determined by a molar ratio of a composition formula: (Sr
_{2- (a + b) A a} B b) x (Na 1-c K c) y (Nb 5-d C
_d ) It was weighed so that a, b, c, d, x and y at O ₁₅ became the values shown in Table 1. This mixture was wet-mixed in a ball mill using ZrO ₂ balls for 12 hours. Next, after drying this mixture, 900-110
The calcined product was calcined at 0 ° C. for 3 hours, and the calcined product was pulverized again by the ball mill. Then, a binder (PVA) is added to the pulverized material.
Was mixed and granulated. 1.5 t / cm ^{2 of the} obtained powder
At a pressure of 5 mm to form a cylinder having a diameter of 5 mm and a thickness of 8 mm.

These compacts are arranged on a plate made of MgO, and are heated at 1200 ° C. to 1280 ° C. in the air.
Fired for ~ 5 hours. The obtained porcelain was measured by X-ray diffraction measurement.
a tungsten bronze-type composite oxide represented by r ₂ NaNb ₅ O ₁₅ or Sr ₂ KNb ₅ O _15;
1/2 Li _1/2 ), (Bi _1/2 Na _1/2 ) and (Bi
_1/2 K _1/2 ), Mg, Ca and B
It was confirmed that at least one of a, or a crystal phase in which V or Ta was dissolved was mainly used.

A silver electrode is baked on the obtained piezoelectric ceramic,
5 to 8 kV / mm in silicon oil at 20 to 150 ° C
Was applied to perform polarization processing. The relative permittivity (ε _{33 T} / ε ₀ ) and the longitudinal resonance / anti-resonance frequency are measured at room temperature using an impedance analyzer to calculate the electromechanical coupling coefficient (k ₃₃ ) and the elastic compliance (S _33E ). and, porcelain piezoelectric strain constant (d ₃₃₎
I asked.

Further, the relative permittivity (ε _33T /
By plotting ε ₀ ) 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 Table 2.

[0028]

[Table 1]

[0029]

[Table 2]

From Tables 1 and 2, it can be seen that the samples of the present invention all have a Curie temperature (Tc) higher than 150 ° C. Moreover, the piezoelectric strain constant (d ₃₃ ) is 1
It is excellent at 00 pC / N or more, particularly 150 pC / N or more, and it can be seen that it is at a practical level as a piezoelectric ceramic.

On the other hand, a part of Sr ₂ NaNb ₅ O ₁₅ is converted to Ca
In the conventional composition substituted by the above, the piezoelectric strain constant (d ₃₃ ) is 5
It turns out that it is as low as 9 pC / N (sample No. 1).

Further, it can be seen that the substitution amount a of Sr with Mg, Ca, and Ba has a peak of the piezoelectric strain constant (d ₃₃ ) between 0.10 and 0.65 (sample Nos. 19 to 19).
23). (Bi _1/2 Li _1/2 ), (Bi _1/2 Na)
_It can be seen that the Curie temperature (Tc) decreases and the piezoelectric strain constant (d ₃₃ ) increases as the amount of substitution b by ( _1/2 ) and (Bi _1/2 K _1/2 ) increases (Sample No. 2). ~ 5).

Further, it can be seen that when a part of Na is replaced with K, the Curie temperature (Tc) is lowered and the piezoelectric strain constant (d ₃₃ ) is further improved (Sample Nos. 15 to 18).

The replacement amount d of Nb by V is 0.01
It has a peak of the piezoelectric strain constant (d ₃₃ ) between の 間 0.10 and the Curie temperature (Tc) gradually increases (samples Nos. 6 to 10). On the other hand, as the substitution amount d of Nb with Ta increases, the piezoelectric strain constant (d ₃₃ ) gradually increases, but the Curie temperature (Tc) decreases (samples Nos. 11 to 14).

On the other hand, 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 (Tc) gradually increases as x increases. (Sample Nos. 24 to 28). y is a peak exists in the piezoelectric strain constant (d ₃₃₎ between 0.80 to 1.20, the Curie temperature (Tc) is gradually to be seen higher with an increase of y (sample No.29~32 ).

Sample No. For 33-35, 200
Despite having a high Curie temperature (Tc) of ℃
It can be seen that the piezoelectric strain constant (d ₃₃ ) is excellent at 120 pC / N or more. In Table 1, BiLi, BiNa, B
The _{iK, (Bi 1/2 Li 1/} 2), (Bi 1/2 N
a _1/2 ) and (Bi _1/2 K _1/2 ).

[0037]

As described above, according to the piezoelectric ceramic of the present invention, the Curie temperature (Tc) is higher than 150 ° C.
A lead-free piezoelectric ceramic having a piezoelectric strain constant (d ₃₃ ) of 100 pC / N or more and practically usable as a piezoelectric material for a laminated actuator can be provided. Since it does not contain lead, it does not adversely affect the environment due to elution of lead by acid rain.

Claims (4)

[Claims] 1. A tungsten bronze composite oxide represented by the general formula: Sr ₂ NaNb ₅ O ₁₅ , wherein part of Sr is (Bi _1/2 Li _1/2 ) or (Bi _1/2 Na _{1 / 2} ) and at least one of (Bi _1/2 K _1/2 ) and M
A piezoelectric ceramic mainly comprising crystal grains substituted with at least one of g, Ca and Ba. 2. The piezoelectric ceramic according to claim 1, wherein a part or all of Na is substituted with K and a part of Nb is substituted with V and / or Ta. 3. A formula according to the atomic ratio _{(Sr 2- (a + b)} A a B b) x (Na 1-c K c) y (Nb
_{5-dV d} ) O ₁₅ , where a, b, c, d, x and y are 0.10 ≦ a ≦ 0.65 0 <b ≦ 0.40 0 ≦ c ≦ 1.00 ≦ d ≦ 0.10 0.96 ≦ x ≦ 1.04 0.80 ≦ y ≦ 1.20 A ... At least one of Mg, Ca and Ba
seed. B: (Bi _1/2 Li _1/2 ), (Bi _1/2 Na _1/2 )
The piezoelectric ceramic according to claim 1 or 2, wherein at least one of (Bi1 _/ 2K1 _{/ 2} ) is satisfied. Wherein the composition formula by atomic ratio _{(Sr 2- (a + b)} A a B b) x (Na 1-c K c) y (Nb
_5-d Ta _d ) O _{15 where} a, b, c, d, x and y are 0.10 ≦ a ≦ 0.65 0 <b ≦ 0.40 0 ≦ c ≦ 1.00 ≦ d ≦ 0.50 0.96 ≦ x ≦ 1.04 0.80 ≦ y ≦ 1.20 A ... At least one of Mg, Ca and Ba
seed. B: (Bi _1/2 Li _1/2 ), (Bi _1/2 Na _1/2 )
The piezoelectric ceramic according to claim 1 or 2, wherein at least one of (Bi1 _/ 2K1 _{/ 2} ) is satisfied.