JP2874495B2 - Piezoelectric material - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a piezoelectric ceramic material based on lead titanate (PbTiO ₃ ), and more particularly to a piezoelectric ceramic material used for a piezoelectric vibrator, a resonator, a ceramic filter and the like.

[0002]

2. Description of the Related Art Piezoelectric ceramic materials have conventionally been used as piezoelectric materials by taking advantage of the fact that distortion occurs when an electric field is applied. For example, piezoelectric ceramic materials include piezoelectric vibrators, piezoelectric resonators, piezoelectric oscillators, and ceramics. Examples include a filter, a surface acoustic wave filter, and a pyroelectric element. As is well known, piezoelectric ceramic materials of this type include those containing PbTiO ₃ as a main component or those containing Pb (Ti, Zr) O ₃ as a main component, and further include a second component or a third component. As Pb (Mn _1/3 Nb _2/3 ) O
₃ , Pb (Ni _1/3 Nb _2/3 ) O _{3 and the} like are available.

[0003] Among them, PbTiO ₃ piezoelectric ceramic material is
Various studies have been made on the modified position, and a piezoelectric porcelain material that has a large electromechanical coupling coefficient for vibration in the thickness direction compared to vibration in the spreading direction and a small dielectric constant has been found. (JP-A-61-236176).

[0004]

The above-mentioned conventional PbTiO ₃
Thermal aging (temporal change) for system piezoelectric ceramic materials
The characteristics are inferior, and there is a problem that if the PbTiO ₃ -based piezoelectric ceramic is left at a high temperature, the piezoelectric characteristics and the electric characteristics are rapidly deteriorated with time.

[0005] Further, there has been another problem that the device is unstable even against a rapid change in ambient temperature (thermal shock), and the resonance frequency is liable to change when subjected to a thermal shock.

Further, the PbTiO ₃ -based piezoelectric ceramic material containing the above-mentioned additives such as Pb (Mn _1/3 Nb _2/3 ) O ₃ is hard to be sintered, and it is difficult to obtain a dense structure. There is also a problem that characteristics are deteriorated and polarization is difficult.

[0007] The present invention has been made in view of the above-mentioned problems, and has good thermal aging characteristics, stable resonance frequency against thermal shock, and improved sintering characteristics during firing. An object of the present invention is to provide a PbTiO ₃ -based piezoelectric ceramic material having a dense structure and excellent polarization characteristics.

[0008]

Means for Solving the Problems In order to achieve the above object, a piezoelectric ceramic material according to the present invention comprises yPb (Fe _1/3 Nb _2/3 ) O ₃ −
(1-y) {Pb _{a-3x / 2} (La _1-z Nd _z ) _x } TiO ₃ (where x = 0.02 ~
0.20, y = 0.01-0.10, z = 0.02-1.0, a = 0.9-1.1
) As the main component, and the {Pb _{a-3x / 2} (La _1-z N
d _{z) x}} a part of Pb is Ca among TiO ₃ component, Sr, substituted with at least one element of Ba, it is characterized in that it further contains MnO ₂ (1). Further, in the piezoelectric ceramic material according to the present invention, in the piezoelectric ceramic material according to the above (1), part of Pb in the {Pb _{a-3x / 2} (La _1-z Nd _z ) _x } TiO ₃ component is Ca , Sr, and Ba are substituted by at least one element in an amount of 1 to 10 mol%, and MnO ₂ is added in an amount of 0.1 to 2.0 wt%.
It is characterized by containing (2).

In the piezoelectric ceramic material described above, the values of x and z in the main component, the value of y in the main component, the amount of MnO ₂ contained in the main component, or the {Pb _{a-3x / 2} (La
_1-z Nd _z ) _x } C which partially replaces Pb in the TiO ₃ component
If the amount of at least one of a, Sr, and Ba exceeds the upper and lower limits of the above-described predetermined range, the characteristics thereof are deteriorated.
The value of x in the main component is {Pb _{a-3x / 2} (La _1-z Nd _z ) _x } TiO
It is a value related to the ratio of the _three components Pb and (La _1-z Nd _z ),
When the value of x is in the range of 0.02 to 0.20, the sintering characteristics of the porcelain are good, but when it is less than 0.02, the grain growth is remarkable, it becomes difficult to obtain a dense piezoelectric ceramic, and it exceeds 0.20. In this case, the piezoelectric characteristics such as the electromechanical coupling coefficient (Kt) of the vibration in the thickness direction tend to deteriorate.

The value of y in the main component is two components of the main component, Pb (Fe _1/3 Nb _2/3 ) O ₃ and {Pb _{a-3x / 2} (La _1-z Nd _z ) _x } TiO
_When the value of y is less than 0.01, the rate of change of the resonance frequency becomes large when subjected to a thermal shock, and when the value of y exceeds 0.10, the electromechanical coupling of the vibration in the spreading direction is performed. Since the coefficient (Kp) increases, the electromechanical coupling coefficient (Kp) and the electromechanical coupling coefficient (K
The value of Kt / Kp, which is the ratio of t), becomes small, and the resonance frequency characteristic of the vibration in the thickness direction tends to deteriorate.

[0011] The amount of MnO ₂ contained in the main component is 0.
If the amount is less than 1% by weight, the sintering characteristics of the piezoelectric ceramic deteriorate, and it becomes difficult to obtain a dense sintered body. On the other hand, when the content exceeds 2.0% by weight, the specific resistance of the piezoelectric ceramic material becomes small, so that polarization becomes difficult.

In the above {Pb _{a-3x / 2} (La ₁ -zNd _z ) _x } TiO ₃ component, the amount of at least one of Ca, Sr, and Ba partially substituted for Pb is less than 1 mol%. In the case of (1), the thermal aging characteristic tends to deteriorate, and when it exceeds 10 mol%, the Curie point decreases, and the piezoelectric characteristic also tends to deteriorate.

The value of z in the main component is {Pb
_{a-3x / 2 (La 1} -z Nd z) x} La was substituted for Pb position of TiO ₃ component
_1-z Nd _z is a value related to the proportion of, for z = 1, that is, the sintering properties are improved even in the presence of Nd alone, if z weight is less than 0.02 poor temperature characteristics of the resonance frequency Tend to fall.

Further, since Pb is quantitatively flexible,
_1-z Nd _z) ± from the amount of _x in terms of corrected taking into account the valency 0.0
0 to 0.10 mol, that is, the value of a can be increased or decreased in the range of 0.9 to 1.1. When the value of a exceeds 1.1, it is difficult to obtain a dense piezoelectric ceramic due to remarkable grain growth in the firing step, and when the value of a is less than 0.9, the electromechanical coupling coefficient (Kt) of vibration in the thickness direction, etc. Tend to degrade the piezoelectric characteristics of.

[0015]

According to the above construction, the main component is yPb (Fe
_{1/3 Nb 2/3) O 3 - (} 1-y) {Pb
_{a-3x / 2 (La 1} -z Nd z) x} TiO 3 ( where, x-0.02~0.20, y-0.01~0.1
0, z = 0.02 to 1.0) a = a value in the range of 0.9 to 1.1), and Pb (Fe _1/3 N
Since b _2/3) containing the O ₃ component are improved sintering characteristics to become a dense sintered body, and changes in resonant frequency even when subjected to thermal shock is reduced.

Further, {Pb _{a-3x / 2} (La _1-z N
In d _{z) x}} TiO ₃ component, part of Pb is Ca, Sr, B
Since it is replaced by at least one of a, the polarization of the piezoelectric ceramic is stabilized, and the absolute value of the thermal aging characteristic is reduced.

Also, {Pb _{a-3x / 2} (La _1-z N
Since part of Pb is replaced by Nd in the d _z ) _x } TiO ₃ component, the crystal lattice becomes more isotropic, the occurrence of crystal distortion due to temperature change is reduced, and the temperature of the resonance frequency is reduced. The characteristics are improved.

Further, {Pb _{a-3x / 2} (La _1-z N
In the d _z ) _x } TiO ₃ component, a part of Pb is replaced by La and Nd, so that the crystal lattice becomes more isotropic, anisotropic grain growth of the grains is suppressed, and the sintering properties are reduced. Has been improved,
Further, since MnO ₂ is contained, the MnO ₂ serves as a sintering aid to further improve the sintering characteristics, and the sintered body has a dense structure and is easily polarized.

[0019] In the piezoelectric ceramic material of (1), at least one of the _{{Pb a-3x / 2 (} La 1-z Nd z) x} a part of Pb is Ca among TiO ₃ component, Sr, Ba 1 to 10 depending on the element
When substituted by mol% and further containing 0.1 to 2.0% by weight of MnO ₂ , the heat aging characteristics and the like are further improved, and the sintered body becomes more dense and easily polarized.

[0020]

Examples and Comparative Examples Examples of piezoelectric ceramic materials according to the present invention will be described below. PbO (or Pb ₃ O as raw material
_{4), TiO 2, La 2} O 3, Nd 2 O 3, CaCO 3, SrCO 3, BaC
Using O ₃ , Fe ₂ O ₃ , Nb ₂ O ₅ , and MnO ₂ , the compositions shown in Table 1 below were weighed and wet-mixed in a pot mill. As a raw material, a compound that eventually becomes the above oxide, for example, MnCO ₃ or the like may be used instead of MnO ₂ . After the wet mixing, the mixture was dehydrated and dried, and calcined at 800 to 1100 ° C for 2 hours. Next, the calcined powder is further pulverized by using a pot mill or the like, and then an organic binder is added thereto, so that 0.5 to 2.0 t / cm ²
It was pressed into a disc having a diameter of 20 mm and a thickness of 1.5 mm under a moderate pressure, and then calcined at a temperature of about 1200 to 1300 ° C. for 2 hours to obtain a piezoelectric ceramic. The piezoelectric ceramic obtained in this way is 0.5 mm thick
After polishing, electrodes are formed on both sides by silver evaporation,
The polarization treatment was performed at 150 ° C. and 2 to 6 KV / mm for about 10 minutes.

The piezoelectric properties and electrical properties of the piezoelectric ceramic obtained by the above steps were measured. That is, the thermal aging characteristics of the electromechanical coupling coefficient (Kt) of the thickness direction vibration, the rate of change of the resonance frequency (fr) of the thickness direction vibration after thermal shock, the temperature coefficient, and the electromechanical coupling coefficient (Kt) of the thickness direction vibration. It was measured. The results are shown in Table 1 below.

The conditions of the thermal shock are as follows: the temperature of the piezoelectric ceramic is lowered to -40 ° C., and the temperature is raised to 80 ° C.
Leave for a minute. Perform the same operation with the above operation as one cycle
Repeated 100 cycles.

The measurement of the temperature coefficient was performed in the range of -20 ° C to 80 ° C.

The thermal aging characteristic is shown by the rate of change of the electromechanical coupling coefficient (Kt) of the vibration in the thickness direction before and after heat treatment at 200 ° C. for 1 hour for each piezoelectric ceramic.

The temperature coefficient of the resonance frequency (ppm / ° C.)
Is a value obtained by the following equation.

[0026]

(Equation 1)

In Table 1, the asterisks indicate those of Comparative Examples which are outside the scope of the present invention, and all other examples are those within the scope of the present invention.

[0028]

[Table 1]

[0029]

[Table 1-2]

As is apparent from Table 1, the value of y is 0, that is, No. 5 containing no Pb (Fe _1/3 Nb _2/3 ) O _3.
In this case, the sintered density is low, and the amount of change in the resonance frequency after thermal shock is large. In No. 16 in which substitution with Ca, Sr, and Ba was not performed, the heat aging characteristics were not improved.

No. 20 having a large amount of MnO ₂ is difficult to polarize,
No. 15 which does not contain MnO ₂ has no improvement in the resonance frequency change rate after thermal shock and the thermal aging characteristics. The value of x is 0, that is, La and Nd are not contained at all.
No. 26 and No. 27 having a large amount of Pb both had difficulty in sintering.

In the case of No. 31 having a small amount of PbO, neither the change rate of the resonance frequency after the thermal shock nor the thermal aging characteristic was improved.

No. 24 in which the value of z is 0, that is, No. 24 containing no Nd, has a large temperature coefficient.

In contrast to these comparative examples, those within the scope of the present invention are, as apparent from Table 1, the electromechanical coupling coefficient (Kt) of the vibration in the thickness direction and the resonance frequency (fr) of the vibration in the thickness direction. The rate of change after thermal shock, the temperature coefficient, and the electromechanical coupling coefficient (Kt of the thickness direction vibration) all show favorable values.

[0035]

As described above in detail, in the piezoelectric ceramic material according to the present invention, yPb (Fe _1/3 Nb _2/3 ) O ₃ − (1−y) {Pb
_{a-3x / 2} (La _1-z Nd _z ) _x } TiO ₃ (where x = 0.02 to 0.20, y =
0.01 to 0.10, z = 0.02 to 1.0, a = a value in the range of 0.9 to 1.1) as the main component, and the {Pb _{a-3x / 2} (La _1-z Nd _z ) _x } TiO
Of the _three components, Pb is partially replaced by at least one element of Ca, Sr, and Ba, and further contains MnO ₂ , so that the thermal aging characteristics are good, the resonance frequency against thermal shock is stable, and the temperature is low. A PbTiO ₃ piezoelectric ceramic material having a small change in resonance frequency, a small temperature coefficient, improved sintering characteristics during firing, a dense structure, and excellent polarization characteristics can be obtained.

Further, at least one in the piezoelectric ceramic material, a portion of the _{{Pb a-3x / 2 (} La 1-z Nd z) x} Pb among TiO ₃ component Ca, Sr, and Ba of (1) 1 to 10 depending on the element
are mol% substituted, if further containing the MnO ₂ 0.1 ~ 2.0 wt%, thermal aging characteristics, etc. can be more improved, be more becomes dense sintered body, to obtain a polarization easily PbTiO ₃ based piezoelectric ceramic material it can.

Therefore, the obtained piezoelectric ceramic material is suitably used for applications such as a pyroelectric element, a resonator, and a filter. In particular, when the piezoelectric ceramic material is used as a reference symbol of a digital IC or an oscillator used for an oscillation circuit. Demonstrates excellent effects.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) C04B 35/42-35/49 H01L 41/18

Claims (2)

(57) [Claims] (Claim 1) yPb (Fe _1/3 Nb _2/3 ) O ₃ − (1−y) {Pb
_{a-3x / 2} (La _1-z Nd _z ) _x } TiO ₃ (where x = 0.02 to 0.20, y =
0.01 to 0.10, z = 0.02 to 1.0, a = a value in the range of 0.9 to 1.1) as the main component, and the {Pb _{a-3x / 2} (La _1-z Nd _z ) _x } TiO
A piezoelectric ceramic material characterized in that a part of Pb among the _three components is replaced by at least one element of Ca, Sr, and Ba, and further contains MnO ₂ . 2. A part of Pb in the {Pb _{a-3x / 2} (La ₁ -zNd _z ) _x } TiO ₃ component is substituted by 1 to 10 mol% with at least one element of Ca, Sr and Ba. , And MnO _{2 in the range} of 0.1 to 2.0
The piezoelectric ceramic material according to claim 1, wherein the piezoelectric ceramic material is contained by weight%.