JPH0561222B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a piezoelectric composition suitable for a vibrator that generates sound waves, and more specifically, the basic composition is
It consists of a three-component system of PbTiO ₃ , PbZrO ₃ and Pb(Co _1/3 Nb _2/3 )O ₃ , and the A of the structure of perovskite ABO ₃
This invention relates to a piezoelectric ceramic composition in which part of the Pb present in the lattice positions is replaced by Sr ions, Nb present in the B lattice positions is added in a smaller amount than its stoichiometric amount, and MnCO ₃ and WO ₃ are added simultaneously. [Prior art and its problems] Conventionally, piezoelectric ceramic compositions include PZT [Pb
(Ti _x Zr _y ) O ₃ ] system or a ternary system containing a composite oxide with a small amount of additives added, but the PZT system has a very high sintering temperature and is difficult to sinter. Since PbO evaporates during the process, it is difficult to control the exact chemical composition, and the physical properties can be adjusted depending on the application field only by adjusting the additives and the proportions of Zr and Ti, so the range of selection is limited. In a three-component system, the dielectric loss coefficient (tanδ)
is small, and the mechanical quality factor (Mechanical
It was not possible to obtain a material with large values of both quality factor (Qm) and piezoelectric constant (d ₃₃ ).
In general conventional piezoelectric ceramic compositions,
As the value of Qm increases, d ₃₃ decreases, and d ₃₃
As the value of increases, Qm tends to decrease,
In particular, it was unsuitable as a composition for a vibrator. The value of _d33 indicates the degree of displacement caused by the voltage applied to the piezoelectric ceramic element.
The larger d ₃₃ is, the larger the displacement that occurs in the piezoelectric ceramic element in the same electric field, making it suitable for use as a vibrator. Furthermore, when the piezoelectric ceramic vibrates mechanically, the value of Qm is inversely proportional to the energy that is dissipated into heat per cycle and cannot be used again as vibration energy, so the higher the Qm value, the lower the loss in the piezoelectric ceramic element. , and the heat dissipation is reduced. if
If the value of Qm is low, a lot of heat will be dissipated when used as a vibrator, which will accelerate the deterioration of the physical properties of the piezoelectric ceramic element and shorten its life. [Object of the Invention] Therefore, an object of the present invention is to provide a piezoelectric composition used for a vibrator, which has high values of both Qm and d ₃₃ and has a low dielectric loss coefficient. [Means for solving the problems] In order to achieve the above object, the present invention provides PbTiO ₃ −
In the ternary system of PbZrO ₃ −Pb(Co _1/3 Nb _2/3 )O ₃ , the amount of Nb filling the PCN system is generally
After adding a small amount of Pb ions and replacing some of the Pb ions with Sr,
Regarding a piezoelectric ceramic composition characterized in that a small amount of WO ₃ and MnCO ³ (MnO is also possible, but MnCO is described below as a representative for convenience), more specifically, the above three-component system is xPbTiO ₃ −
In the formula expressed by yPbZrO ₃ −zPb(Co _1/3 Nb _2/3 )O ₃ , the molar ratio is 0.43≦x≦0.48, 0.04≦z≦
0.15, and x+y+z=1. Furthermore, the amount of Nb is smaller than the amount of Nb that satisfies general PCN systems.
The limit of quantity is 0<δ≦0.2 in molar ratio, and Pb
The range of a in which is substituted with Sr is 0<a≦ in mol%
It is 0.06. and added mWO ₃ and
The mol% of _nMnCO3 is 0≦m≦2, 0<n, respectively.
≦2.2. Therefore, in the structure of perovskite ABO ₃ in the present invention, the amount of Nb present in the B lattice position is insufficient compared to the amount that satisfies the PCN system, and some of the Pb ions present in the A lattice position are replaced by Sr. For convenience, the structure is expressed as follows, where the amount of Nb lacking is represented by δ, the substitution of Pb with Sr by a amount is represented by a formula, and the final usage formula is represented as follows. (Pb _1-a Sr _a ) {Ti _x Zr _y [Co _1/3 Nb(1-δ) _2/3 ] _Z }O ₃
+ m mol % WO ₃ + n mol % MnCO ₃ In the above formula, expressed as a molar ratio, 0.43≦x≦0.48,
0.04≦z≦0.15, x+y+z+=1, 0<δ≦
0.2, 0≦a≦0.06, expressed in mol%, 0<
m<2, 0<n≦2.2. [Action of the invention] In the piezoelectric composition of the invention, xPbTiO ₃ −
Limiting the content of the _PbTiO3 component in the ternary system (x+y+z=1) of yPbZrO3 _- zPb[Co1 _/3Nb (1-δ) _2/3 ] _O3 in the range of 43 to 47 mol%. This is because both d ₃₃ and Qm are improved and have stable values in this range, and if less than 43 mol% or 48
When there is a mol% excess, d ₃₃ and Qm tend to decrease, which is not desirable. In addition, Pb[Co _1/3
Limiting the content of the Nb(1-δ) _2/3 ]O ₃ component to 4 to 15 mol% prevents the sintering temperature from decreasing due to the inclusion of this component, which is a composite oxide in the form of a compound. However, if the content is less than 4 mol%, the sintering temperature will not drop significantly compared to the conventional PZT binary system, and if the content exceeds 15 mol%, the dielectric loss coefficient will decrease. (tanδ) increases, d ₃₃
The value of is low, making it unsuitable for use in vibrators. By the way, in the three-component system of the present invention, one component Nb
Due to the shortage of (Pb _1-a Sr _a ) {Ti _x Zr _y [Co _1/3 Nb(1
−δ) _2/3 ] _Z }O ₃ +mmol%WO ₃ +nmol%
Although expressed as MnCO ₃ , one component is actually a complex oxide (1-δ)Pb(Co _1/3 Nb _2/3 )O ₃ + (2/3)δPb
(Co _1/2 W _1/2 ) O + (1/3) δpb (Mn _1/2 W _1/2 ) O ₃ , so if we talk about the component system of the present invention in detail,
_PbZrO3 , _PbTiO3 , Pb(CoCo1 _/ 3Nb2 _{/ 3} )O3, Pb
(Co _1/2 W _1/2 ) O ₃ and Pb (Mn _1/2 W _1/2 ) O ₃ are considered to be a solid solution, but Pb
Considering that (CO _1/2 W _1/2 )O ₃ and Pb(Mn _1/2 W _1/2 )O ₃ are small amounts, the above formula was adopted as a three-component system for convenience. In the above three-component system of the present invention, as δ increases, d ₃₃ decreases little by little, but Qm increases to a certain amount and then decreases. Therefore, when δ exceeds 0.2,
This is not desirable because Qm decreases significantly. In partially substituting a part of Pb with Sr in the ternary basic composition of the present invention, it is desirable that the substitution molar ratio a of Sr is in the range of 0 to 0.06, and within that range, d ₃₃ and Qm both increase. However, if you substitute beyond that range, d ₃₃ and
Qm is rather undesirable because it decreases rapidly. The contents of the present invention explained above will be explained in more detail with reference to the attached drawings. FIG. 1 illustrates the optimum composition ratio of the three basic components in the three-component piezoelectric composition of the present invention, where the numbers in the parallel squares indicate the numbers of the examples. Figure 2 shows the amount of insufficient Nb δ set to 0.13, m
and n are fixed to 1.4 and 1.0, respectively, and represent the changes in d ₃₃ and Qm by changing the value of a, which is the replacement value of Sr, that is, (Pb _1-a Sr _a ) {TiO _0.45 Zr _0.45
[Co _1/3 Nb _(1-0.13)2/3 ] _0.1 ] O ₃ + 1.4 mol% WO + 1.0 mol% MnCO ₃ This shows the change in d ₃₃ and Qm due to the change in a of Pb lattice. Sr substituted in position
As the amount of increases, the values of _d33 and Qm also increase, but
When 6 mol% or more is substituted, d ₃₃ and Qm tend to decrease rapidly. Figure 3 shows that the value of a, which is the replacement value of Sr, is 0.04.
The values of m and n are fixed at 1.4 and 1.0, respectively, and the values of changes in d ₃₃ and Qm are expressed by changing the value of the Nb deficiency amount δ. That is, (Pb _1-0.04 Sr _0.04 ) {Ti _0.45 Zr _0.45 [Co _1/3
Nb(1-δ) _2/3 ] _0.01 }O ₃ + 1.4 mol% WO ₃ + 1.0 mol MnCO ₃ This shows the change in d ₃₃ and Qm due to the change in δ, and as δ increases, Qm The value increases rapidly, but after reaching the maximum value, it suddenly begins to decrease again at the 20 mol% line. To reiterate the piezoelectric composition of the present invention,
_PbTiO3 , _PbZrO3 , Pb[Co1 _/3 Nb(1-δ) _2/3 ] _O3
It is a composition consisting of a solid solution of general PCN
In the Pb (Co _1/3 Nb _2/3 ) O ₃ system, some of the Nb is deficient, and this is compensated for with additives of WO ₃ and MnCO ₃ , and some of the Pb is replaced with Sr. It is characterized by further improving d ₃₃ and Qm at the same time through substitution. Generally, when Qm increases, d ₃₃ decreases, but in the present invention, d ₃₃ and Qm can be simultaneously improved because the compositions and composition ratios of all the compositions described above are satisfied in a complex manner. The composition of the present invention has very suitable performance for use in piezoelectric vibrators. [Example] The manufacturing method of the present invention and its effects will be explained in more detail with reference to Examples below. However, the present invention is not limited to the following examples. Example 1-55 PbO, TiO ₂ , ZrO ₂ , CoO, with a purity of 99% or more
After weighing SrCO ₃ , WO ₃ , Nb ₂ O ₅ and MnCO ₃ powders to have the compositions shown in Tables 1 and 2 below, acetone was added using a planetary ball meal, nylon jar and ZrO ₂ balls. This was used as a dispersion medium and wet mixed for 4 hours. The mixed powder was dried in an oven and wet-pulverized using an electrofilter at 830° C. for 2 hours in the same manner as the mixing after baking. The crushed powder is molded under a pressure of 91 tons/cm ² to a thickness of 2 mm and a diameter of 25 mm.
I made a mm disk. The thus obtained molded body was sintered at 1180°C for 2 hours and polished on both sides, then silver electrodes were attached, and a direct current electric field of 3 KV/mm was applied for 15 minutes in insulating oil at 120°C to perform polarization treatment, thereby forming a piezoelectric material. I got it. The piezoelectric ceramic as described above was left at room temperature for 24 hours after polarization, and then its piezoelectric properties and dielectric properties were measured. Piezoelectric properties are measured from the thickness vibration mode, and physical properties are measured using a piezo d ₃₃
Meter (Piezo d ₃₃ Meter, manufactured by Berlin Court)
Measure d ₃₃ using an impedance/gain phase analyzer (Impedance/Gain Phase Analyzer).
phase analyzer; Hp4194A) at 1KHz.
Measure the dielectric properties of Cp, tanδ, resonance frequency, anti-resonance frequency, resonance resistance, etc. and obtain Qm (mechanical quality factor).
and K (electromechanical coupling coefficient) are determined and the respective results are shown in Tables 1 and 2. The formula used for the calculation is as follows. (1/kt ² ) = 0.405 (fRt / Δf) + 0.810 qm = f ² _At / [2πRoCPfR _t (f ² _At − f ² _Rt )] Kt = Electromechanical coupling coefficient in thickness vibration mode f _R = Resonance Frequency f _Rt = Resonant frequency in thickness vibration mode f _A = Anti-resonant frequency f _At = Anti-resonant frequency Δf in thickness vibration mode = (f _At −f _Rt ) Ro = Resonant resistance Cp = Capacitance

【table】

【table】

【table】 [Brief explanation of drawings]

Fig. 1 shows the optimum composition ratio of the three basic components in the ternary piezoelectric composition of the present invention, and Fig. 2 shows the change values of d ₃₃ and Qm with respect to a. , FIG. 3 shows the change values of d ₃₃ and Qm with respect to δ.

Claims (1)

[Claims] 1. Adding Nb in an amount less than the theoretical value to the three-component system of PbTiO ₃ −PbZrO ₃ −Pb(Co _1/3 Nb _2/3 )O ₃ and replacing some of the Pb ions with Sr. and a small amount of _WO3 and _MnCO3
The following formula (Pb _{1-a Sra} ) {Ti _x −Zr _Y − [Co _1/3 Nb _2/3 (1−δ)] _Z
}O ₃ +mmol% _WO3 +nmol% _MnCO3 (However, x, y, z, a, δ, m, n in the formula are,
0.43≦x≦0.48, 0.04≦z≦0.15, x+, respectively
y+z=1, 0<a≦0.06, 0<δ≦0.2, 0<
A piezoelectric ceramic composition represented by m≦2, 0<n≦2.2.