JP2007230792A - Piezoelectric ceramic composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition having a large electromechanical coupling factor and excellent in thermal resistance. <P>SOLUTION: This piezoelectric ceramic composition comprises a sintered compact whose main component is expressed by formula (1): Pb<SB>α</SB>[(Mg<SB>1/3</SB>Nb<SB>2/3</SB>)<SB>x</SB>Ti<SB>y</SB>Zr<SB>z</SB>]O<SB>3</SB>(where α, x, y and z each represents a molar ratio and satisfies following inequalities: 0.985≤α≤1.02; 0.04≤x≤0.06; 0.43≤y≤0.49: 0.47≤z≤0.53; provided that x+y+z=1) and is characterized in that the coercive electric field at 25°C is ≥1.38 kV/mm. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a piezoelectric ceramic composition suitable for a filter, a resonator and the like.

Since it was discovered that a Pb (Zr · Ti) O ₃ composition close to the morphotropic phase boundary exhibits excellent piezoelectricity, this piezoelectric ceramic composition has a high Curie temperature, a temperature change / time change, Since it has an excellent coupling coefficient, it can be used as a filter element.
The piezoelectric ceramic composition has a function of freely converting and taking out electrical energy and mechanical energy, and is used as a filter, a resonator, an actuator, an ignition element, an ultrasonic motor, or the like.
For example, when a piezoelectric ceramic composition is used as a filter, a large electromechanical coupling coefficient is required.
Therefore, for example, in Patent Document 1, the general formula aPb (Mg _1/3 Nb _2/3 ) O ₃ —bPbTiO ₃ —cPbZrO ₃ (a, b, c are 1 ≦ a ≦ 10, 42 ≦ b ≦ 60, 30 respectively. ≦ c ≦ 57, where a, b and c are mol%, and 0.5 to 5 mol% of Pb atoms of lead zirconate titanate represented by a + b + c = 100) are substituted with Mg, and Cr Has proposed a piezoelectric porcelain characterized by containing 0.1 to 1 wt% of Cr ₂ O ₃ in terms of Cr ₂ O ₃ .

Japanese Patent No. 3322241

In recent years, surface-mounted components have been widely used, and a piezoelectric ceramic composition having high heat resistance is required for passing through a solder reflow furnace when mounted on a printed circuit board. That is, a piezoelectric ceramic composition having a large electromechanical coupling coefficient and excellent heat resistance has been required.
The present invention has been made based on such a technical problem, and an object of the present invention is to provide a piezoelectric ceramic composition having a large electromechanical coupling coefficient and excellent heat resistance.

The present inventor newly found out that heat resistance can be improved by increasing the coercive electric field in a piezoelectric ceramic composition containing a perovskite compound containing Pb, Zr and Ti as main components. That is, the present invention relates to Pb _α [(Mg _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ Formula (1)
(In the formula (1), 0.985 ≦ α ≦ 1.02,
0.04 ≦ x ≦ 0.06,
0.43 ≦ y ≦ 0.49,
0.47 ≦ y ≦ 0.53,
x + y + z = 1.
In the formula (1), α, x, y and z each represent a molar ratio. And a coercive electric field composition at 25 ° C. of 1.38 kV / mm or more.
In the present invention, Cr is 0.10 to 0.40 wt% in terms of Cr ₂ O ₃ , Al is 0.005 to 0.050 wt% in terms of Al ₂ O ₃ , and Si is SiO. It is preferable to contain 0.005-0.070 wt% in conversion of ₂ .

  The piezoelectric ceramic composition of the present invention can have an absolute value (| ΔFr |) of heat resistance ΔFr of 10 kHz or less by adopting the above configuration. Although the definition of | ΔFr | will be described later in detail, it is specified by the amount of change in the resonance frequency before and after applying the thermal shock.

  According to the present invention, a piezoelectric ceramic composition having a large electromechanical coupling coefficient and excellent heat resistance is provided by specifying a coercive electric field.

Hereinafter, a piezoelectric ceramic composition according to the present invention will be described in detail based on embodiments.
<Chemical composition>
The piezoelectric ceramic composition according to the present invention includes a perovskite compound containing Pb, Zr, and Ti as main components. Moreover, Cr, Al, and Si can be contained as subcomponents. By including all of Cr, Al, and Si as subcomponents, a piezoelectric ceramic composition having a large electromechanical coupling coefficient kt and excellent heat resistance can be obtained. The inclusion of Cr is effective in increasing the electromechanical coupling coefficient kt and improving the heat resistance. Further, Al and Si contribute to the improvement of strength.

The main component according to the present invention is given by the following formula (1).
Pb _α [(Mg _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ Formula (1)
However, 0.985 ≦ α ≦ 1.02,
0.04 ≦ x ≦ 0.06,
0.43 ≦ y ≦ 0.49,
0.47 ≦ z ≦ 0.53,
In the formula (1), α, x, y and z each represent a molar ratio. Further, x + y + z = 1.

Next, the reasons for limiting α, x, y, and z in formula (1) will be described.
Α indicating the amount of Pb is in the range of 0.985 ≦ α ≦ 1.02. If α is less than 0.985, it is difficult to obtain a dense sintered body. On the other hand, when α exceeds 1.02, good heat resistance cannot be obtained. Therefore, α is preferably in the range of 0.985 ≦ α ≦ 1.02, more preferably 0.99 ≦ α ≦ 1.01, and 0.995 ≦ α ≦ 1.005. More desirable.

  X indicating the Mg amount and the Nb amount is preferably in the range of 0.04 ≦ x ≦ 0.06. When x is less than 0.04, the temperature characteristics are deteriorated. On the other hand, when x exceeds 0.06, good heat resistance cannot be obtained. Therefore, x is preferably in the range of 0.04 ≦ x ≦ 0.06, more preferably 0.04 ≦ x ≦ 0.058, and 0.045 ≦ x ≦ 0.055. Is more desirable.

  Y indicating the amount of Ti is in the range of 0.43 ≦ y ≦ 0.49. If y is less than 0.43, good heat resistance cannot be obtained. On the other hand, if y exceeds 0.49, it is difficult to obtain good temperature characteristics. Therefore, y is preferably in the range of 0.43 ≦ y ≦ 0.49, more preferably 0.44 ≦ y ≦ 0.47, and 0.445 ≦ y ≦ 0.465. Is more desirable.

  Z indicating the amount of Zr is in the range of 0.47 ≦ z ≦ 0.53. When z is less than 0.47 or more than 0.53, good temperature characteristics cannot be obtained. Therefore, z is preferably in the range of 0.47 ≦ z ≦ 0.53, more preferably 0.48 ≦ z ≦ 0.51, and 0.485 ≦ z ≦ 0.505. Is more desirable.

In the piezoelectric ceramic composition of the present invention, Cr is 0.10 to 0.40 wt% in terms of Cr ₂ O ₃ and Al is 0.005 to 0 in terms of Al ₂ O ₃ with respect to the main component. 0.050 wt% and Si can be contained in an amount of 0.005 to 0.070 wt% in terms of SiO ₂ .
When the Cr content is less than 0.10 wt% in terms of Cr ₂ O _{3 with} respect to the main component, the Al content is less than 0.005 wt% in terms of Al ₂ O ₃ , and the Si content is less than 0.005 wt% in terms of SiO ₂ , Cr The effect of increasing the electromechanical coupling coefficient kt and improving the heat resistance, and the effect of improving the strength of Al and Si cannot be fully enjoyed.
On the other hand, when the Cr amount exceeds 0.40 wt% in terms of Cr ₂ O ₃ , the resistance decreases and polarization becomes difficult. When the Al amount exceeds 0.050 wt% in terms of Al ₂ O ₃ , the heat resistance deteriorates even if the Si amount exceeds 0.070 wt% in terms of SiO ₂ .

More preferable range of Cr content is 0.15～0.35Wt% in terms _{of Cr} 2 _{O 3,} more preferable range is 0.20～0.35Wt% in terms _{of Cr} 2 _{O 3.}
A more desirable range of the Al amount is 0.007 to 0.045 wt% in terms of Al ₂ O ₃ , and a more desirable range is 0.01 to 0.03 wt% in terms of Al ₂ O ₃ .
A more desirable range of Si amount is 0.007 to 0.060 wt% in terms of SiO ₂ , and a more desirable range is 0.010 to 0.050 wt%.

  The piezoelectric ceramic composition of the present invention has a coercive field at 25 ° C. of 1.38 kV / mm or more. Here, the ferroelectric has a domain structure like a ferromagnet, and the dipole moment in one domain is directed in the same direction to generate spontaneous polarization. When an electric field E is applied thereto, the change in the polarization P as a whole draws a hysteresis curve as shown in FIG. In other words, once the electric field is applied, the residual polarization Pr remains without returning to the original domain structure even when the electric field is removed. The electric field strength Ec in the reverse direction that cancels this residual polarization Pr is a coercive electric field. In FIG. 2, when the intercept of the x-axis is a coercive electric field, the coercive electric field on the positive side is Ec1, and the absolute value of the coercive electric field on the negative side is Ec2, the coercive electric field Ec is an average value of Ec1 and Ec2.

  It is generally well known that the coercive electric field varies depending on the composition and additives such as Pb, Mg, Nb, Ti, and Zr, but can be changed by changing the firing temperature or the atmosphere during firing. is there. In order to make the coercive electric field 1.38 kV / mm, for example, it can be achieved by setting the firing temperature as high as possible.

<Manufacturing method>
Next, the desirable manufacturing method of the piezoelectric ceramic composition according to the present invention will be described in the order of the steps.
(Raw material powder, weighing)
As a raw material of the main component, an oxide or a powder of a compound that becomes an oxide by heating is used. Specifically, PbO powder, TiO ₂ powder, ZrO ₂ powder, MnCO ₃ powder, or the like can be used. Each raw material powder is weighed so as to have the composition of the formula (1).
Next, with respect to the total weight of each weighed powder, Cr is 0.10 to 0.40 wt% in terms of Cr ₂ O ₃ and Al is 0.005 to 0.050 wt in terms of Al ₂ O ₃ as subcomponents. %, Si is added in an amount of 0.005 to 0.070 wt% in terms of SiO ₂ . Cr ₂ O ₃ powder, Al ₂ O ₃ powder, and SiO ₂ powder are prepared as subcomponent raw material powders. What is necessary is just to select suitably the average particle diameter of each raw material powder in the range of 0.1-3.0 micrometers.
In addition, not only the raw material powder mentioned above but it is good also considering the powder of the complex oxide containing 2 or more types of metals as raw material powder.

(Calcination)
After the raw material powder is wet-mixed, calcination is performed in a range of 700 to 950 ° C. for a predetermined time. The atmosphere at this time may be N ₂ or air. What is necessary is just to select suitably the holding time of calcination in the range of 0.5 to 5 hours.
In addition, after mixing the raw material powder of the main component and the raw material powder of the subcomponent, both were shown to be subjected to calcining, but the timing of adding the raw material powder of the subcomponent is not limited to that described above. Absent. For example, first, only the main component powder is weighed, mixed, calcined and pulverized. And you may make it add and mix a predetermined amount of raw material powder of a subcomponent with the powder of the main component obtained after calcining pulverization.

(Granulation / molding)
The pulverized powder is granulated into granules in order to smoothly execute the subsequent molding process. At this time, a small amount of a suitable binder such as polyvinyl alcohol (PVA) is added to the pulverized powder, and these are mixed well, and then granulated by passing through a 350 μm mesh to obtain granulated powder. Next, the granulated powder is pressure-molded at a pressure of 200 to 300 MPa to obtain a molded body having a desired shape.

(Baking)
After removing the binder added during molding, the molded body is heated and held for a predetermined time within a range of 1100 to 1250 ° C. to obtain a sintered body. The atmosphere at this time may be N ₂ or air. The heating and holding time may be appropriately selected within the range of 0.5 to 4 hours.

(Polarization treatment)
After the electrode for polarization treatment is formed on the sintered body, the polarization treatment is performed. In the polarization treatment, an electric field of 1.0 to 2.5 Ec (Ec is a coercive electric field) is applied to the sintered body at a temperature of 50 to 300 ° C. for 0.5 to 30 minutes.
When the polarization treatment temperature is less than 50 ° C., Ec increases, so that the polarization voltage increases and polarization becomes difficult. On the other hand, when the polarization treatment temperature exceeds 300 ° C., the insulation of the insulating oil is remarkably lowered, so that polarization becomes difficult. Therefore, the polarization treatment temperature is 50 to 300 ° C. A desirable polarization treatment temperature is 60 to 250 ° C, and a more desirable polarization treatment temperature is 80 to 200 ° C.
Moreover, if the electric field to be applied is less than 1.0 Ec, polarization does not proceed. On the other hand, when the applied electric field exceeds 2.5 Ec, the actual voltage becomes high and the sintered body tends to break down, making it difficult to produce a piezoelectric ceramic composition. Therefore, the electric field applied during the polarization treatment is 1.0 to 2.5 Ec. A desirable applied electric field is 1.1 to 2.2 Ec, and a more desirable applied electric field is 1.3 to 2.0 Ec.

When the polarization treatment time is less than 0.5 minutes, the polarization is insufficient and sufficient characteristics cannot be obtained. On the other hand, when the polarization treatment time exceeds 30 minutes, the time required for the polarization treatment becomes long and the production efficiency is inferior. Therefore, the polarization treatment time is 0.5 to 30 minutes. A desirable polarization treatment time is 0.7 to 20 minutes, and a more desirable polarization treatment time is 0.9 to 15 minutes.
The polarization treatment is performed in an insulating oil heated to the above-described temperature, for example, a silicon oil bath. The polarization direction is determined according to a desired vibration mode. Here, when the vibration mode is thickness longitudinal vibration, the polarization direction is the direction shown in FIG.

After the piezoelectric ceramic composition is polished to a desired thickness, a vibrating electrode is formed. Next, after being cut into a desired shape by a dicing saw or the like, it functions as a piezoelectric element.
The piezoelectric ceramic composition in the present invention is suitably used as a material for piezoelectric elements such as filters, resonators, actuators, ignition elements, and ultrasonic motors.

By selecting a composition recommended by the present invention, the electromechanical coupling coefficient kt can be 30% or more, and further 35% or more. Further, the heat resistance | ΔFa | can be set to 10 kHz or less, further 8 kHz or less, and more preferably 6 kHz or less.
Here, the electromechanical coupling coefficient kt in the present invention is measured using an impedance analyzer (HP4194A manufactured by Hured Packard) at a measurement frequency of about 10 MHz. The electromechanical coupling coefficient kt was obtained based on the following formula (2).

kt ² = (π / 2) · (fr / fa) · cot ((π / 2) · (fr / fa)) (2)
fr: resonance frequency fa: anti-resonance frequency

Further, | ΔFa | in the present invention was determined as follows.
The sample was wrapped with aluminum foil, impregnated in a solder bath at 250 ° C. for 30 seconds, the aluminum foil was removed, and then left at room temperature for 1 hour, and the resonance frequency (Fa ₁ ) was measured. Further, after 100 hours had passed thereafter, the resonance frequency (Fa ₁₀₀ ) was measured again and determined by the equation | ΔFa | = | Fa ₁ -Fa ₁₀₀ |. In the examples described later, | ΔFa | was determined in the same procedure.

As starting materials, lead oxide (PbO) powder, titanium oxide (TiO ₂ ) powder, zirconium oxide (ZrO ₂ ) powder, manganese carbonate (MnCO ₃ ) powder, niobium oxide (Nb ₂ O ₅ ) powder, chromium oxide (Cr ₂₎ O ₃ ) powder, aluminum oxide (Al ₂ O ₃ ) powder, and silicon oxide (SiO ₂ ) powder were prepared.
This raw material powder was weighed so as to have the composition shown in Table 1, and then ball mill mixed for 0.5 hour with Zr balls in pure water. After the obtained slurry was sufficiently dried, it was press-molded and calcined at 800 to 950 ° C. in the air.
The calcined body was pulverized with a ball mill (average particle size: 0.7 μm) and then dried. An appropriate amount of PVA was added as a binder to the finely pulverized powder and granulated.
About 3 g of the granulated powder was placed in a mold cavity having a length of 20 mm and a width of 20 mm, and molded with a load of 245 MPa using a uniaxial press molding machine. After the binder was removed by heating the molded sample, it was fired at 1170 to 1250 ° C. for 2 hours to obtain a porcelain sample.

  After both surfaces of the porcelain sample were processed to a thickness of 0.3 mm with a lapping machine, they were cut into a length x width = 15 mm x 15 mm with a dicing saw, and a temporary electrode for polarization (vertical x width = 14 mm x 14 mm) on both sides ) Was formed. Thereafter, a polarization treatment was performed by applying an electric field of 3 kV / mm for 30 minutes in a silicone oil bath at a temperature of 120 ° C. The polarization direction was the direction shown in FIG. Thereafter, the temporary electrode was removed. The sample size after removal of the temporary electrode is 15 mm long × 15 mm wide × 0.3 mm thick. After polishing again to a thickness of approximately 0.22 mm with a lapping machine, the wafer was cut with a dicing saw into length × width = 7.5 mm × 7.0 mm.

As shown in FIG. 4, the vibrating electrode 2 was formed on both surfaces (polished both surfaces) of the test piece 1 using a vacuum vapor deposition apparatus, and a sample for measuring the electromechanical coupling coefficient kt was obtained. FIG. 5 shows a cross section of the test piece 1 (cross section in the XX direction in FIG. 4), and the overlap of the vibrating electrode 2 is 1.0 mm. The vibrating electrode 2 is composed of a Cr underlayer having a thickness of 0.01 μm and Ag having a thickness of 2 μm.
For each measurement sample, the electromechanical coupling coefficient kt was calculated from the above equation (2). The results are shown in Table 1. All the samples according to the present invention have an electromechanical coupling coefficient kt of 35% or more.

In addition, the front and back surfaces of the porcelain sample were flattened to a thickness of 0.35 mm with a lapping machine, and then cut into vertical x horizontal = 6 mm x 6 mm with a dicing saw, and Ag electrodes were formed on both the front and back surfaces by vacuum evaporation to form residual polarization. A sample for (Pr) measurement was obtained. The obtained sample was applied with 2000V by RT-6000HVS manufactured by Radiant Technology in a 25 ° C. silicone oil bath, the PE hysteresis curve (FIG. 2) was measured, and the coercive electric field was determined as described above. The results are shown in Table 1.
Further, the heat resistance | ΔFa | was determined by the above-described method for the sample whose electromechanical coupling coefficient kt was measured. The results are shown in Table 1.

  FIG. 1 shows the relationship between the coercive electric field and heat resistance | ΔFa | obtained as described above. As shown in FIG. 1, it was found that there is a correlation between the coercive electric field and the heat resistance | ΔFa |. The composition of the sample plotted in FIG. 1 is diverse, and basically this correlation is established regardless of the composition. In order to set the heat resistance | ΔFa | to 10 kHz or less, the coercive electric field needs to be 1.38 kV / mm or more. In order to obtain high heat resistance | ΔFa |, the coercive electric field is preferably 1.4 kV / mm or more, more preferably 1.6 kV / mm or more, and more preferably 1.8 kV / mm or more. The coercive electric field is about 2.0 kV / mm at maximum.

  On the other hand, sample numbers 39 and 40, sample numbers 42 and 43, and sample numbers 44 and 45 in Table 1 have the same main component and subcomponent. However, the coercive electric fields are different from each other, and Sample No. 40, Sample No. 43, and Sample No. 45 having larger coercive electric fields have better heat resistance | ΔFa |. The reason why the coercive electric fields are different while these samples have the same composition is that the firing temperatures are different. That is, sample numbers 39, 42, and 44 have a firing temperature of 1160 ° C, while sample numbers 40, 43, and 45 have a firing temperature of 1250 ° C.

In Table 1, let us focus on α (Pb amount). When α is as small as 0.980 or as large as 1.025, the coercive electric field is low and the heat resistance | ΔFa | is inferior.
Further, for example, by comparing the coercive electric fields of the following sample numbers, it can be seen that the coercive electric field tends to decrease as α increases.
Sample number 4, 13, 26, 40
Sample number 5, 14, 27, 41
Sample number 6, 15, 28, 43
Sample number 7, 16, 29, 45

In Table 1, attention is paid to x (Mn and Nb amounts). For example, by comparing the coercive electric field of the following sample numbers, it can be seen that the coercive electric field tends to increase as x increases.
Sample number 10, 14, 29
Sample number 23, 27, 32
Sample number 36, 41, 48

In Table 1, attention is paid to y (Ti amount). For example, by comparing the coercive electric fields of the following sample numbers, it can be seen that the coercive electric field tends to increase as y increases. This tendency is opposite for z (Zr amount), and the coercive electric field tends to decrease as z increases.
Sample numbers 3-7, sample numbers 12-16, sample numbers 25-29, sample numbers 34-37

It is a graph which shows the relationship between a coercive electric field and heat resistance | (DELTA) Fa |. It is a figure which shows the example of a PE hysteresis curve. It is a figure which shows the polarization direction in case vibration mode is thickness longitudinal vibration. It is a perspective view of the test piece in which the vibration electrode was formed. It is sectional drawing of the XX direction of FIG.

Explanation of symbols

  1 ... Test piece, 2 ... Vibrating electrode

Claims (2)

Pb _α [(Mg _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ Formula (1)
(In the formula (1), 0.985 ≦ α ≦ 1.02,
0.04 ≦ x ≦ 0.06,
0.43 ≦ y ≦ 0.49,
0.47 ≦ z ≦ 0.53,
x + y + z = 1.
In the formula (1), α, x, y and z each represent a molar ratio. ) And a sintered body having a main component represented by
A piezoelectric ceramic composition having a coercive electric field at 25 ° C. of 1.38 kV / mm or more. For the main component, Cr is 0.10 to 0.40 wt% in terms of Cr ₂ O ₃ , Al is 0.005 to 0.050 wt% in terms of Al ₂ O ₃ , and Si is in terms of SiO _{2 as} subcomponents. It contains 0.005-0.070 wt%, The piezoelectric ceramic composition of Claim 1 characterized by the above-mentioned.

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