JP4442467B2 - Piezoelectric ceramic composition - Google Patents

Description

The present invention relates to a piezoelectric ceramic composition suitable for a resonator and the like, and more particularly, to a piezoelectric ceramic composition having excellent heat resistance and electrical characteristics _Qmax .

Most piezoelectric ceramic compositions that are currently in practical use have strong perovskite structures such as tetragonal or rhombohedral PZT (PbZrO ₃ —PbTiO ₃ solid solution) systems and PT (PbTiO ₃ ) systems near room temperature. It is composed of a dielectric.

A piezoelectric ceramic composition has a function of freely converting and extracting electrical energy and mechanical energy, and is used as a resonator, a filter, an actuator, an ignition element, an ultrasonic motor, or the like. For example, when a piezoelectric ceramic composition is used as a resonator, it is required that Q _max as an electrical characteristic (Q _max = tan θ: θ is a phase angle) is large. In recent years, surface-mounted components have become widespread, and when mounted on a printed circuit board, high heat resistance is required to pass through a solder reflow furnace. Therefore, by replacing the third component such as Pb (Mg _1/3 Nb _2/3 ) O ₃ or Pb (Mn _1/3 Nb _2/3 ) O ₃ or adding various subcomponents, (For example, Patent Document 1 (Japanese Patent Laid-Open No. 2000-103684, Patent Document 2 (Japanese Patent Laid-Open No. 2003-128462)).

JP 2000-103694 A JP 2003-128462 A

However, piezoelectric ceramic compositions have been proposed heretofore, could not be combine excellent heat resistance and electrical characteristics Q _max. The present invention has been made based on such a technical problem, and an object thereof is to provide a piezoelectric ceramic composition having excellent heat resistance and electrical characteristics _Qmax .

The present inventors examined improvement in heat resistance by using the rate of change of oscillation frequency before and after applying thermal shock to the piezoelectric ceramic composition as an index of heat resistance. As a result, there is a correlation between the heat resistance and the remanent polarization (Pr), and by controlling the remanent polarization within a predetermined range, it will be described in detail that an extremely excellent heat resistance that | ΔF ₀ | I was able to prepare. It has been found that such remanent polarization can be controlled by the type and amount of subcomponents added in addition to the main components constituting the piezoelectric ceramic composition, and further by the composition of the main components. The present invention is based on such new knowledge, and Pbα [(Mn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ Formula (1) (in Formula (1), 0.96 ≦ α ≦ 1.01, 0.04 ≦ x ≦ 0.16, 0.48 ≦ y ≦ 0.58, 0.32 ≦ z ≦ 0.42, x + y + z = 1, in formula (1) , Α, x, y, and z each represents a molar ratio.), And the residual polarization at 150 ° C. is from 23.81 to 13.31 μC / cm ^2. And a piezoelectric ceramic composition.

In order to obtain a sintered body having a remanent polarization at 150 ° C. of 23.81 to 13.31 μC / cm ^{2 as} in the piezoelectric ceramic composition of the present invention, the subcomponent is selected by the above formula (1). It is effective to specify α of the main component shown. When obtaining a piezoelectric ceramic composition comprising a sintered body, subcomponents are added based on various purposes. Depending on the type of the subcomponent, the remanent polarization at 150 ° C. can be set to 23.81 to 13.31 μC / cm ² . Specifically, Al as an auxiliary component, Ta, Ru using at least one element selected from Cr and Sc. This element, 0.01~15.0wt% in the terms of oxides (except, Al is 0.20~15.0wt%) Ru is contained in the range of.

According to the present invention, a piezoelectric ceramic composition having excellent electrical characteristics Q _max and heat resistance can be provided.

<Residual polarization>
Piezoelectric elements are polarized by direct high voltage, give direction to the direction of spontaneous polarization inside, and have residual polarization (Pr) to obtain piezoelectricity. The present inventors have confirmed that there is a correlation between this residual polarization (Pr) and heat resistance, specifically | ΔF ₀ | shown below.
Here, the heat resistance in the present invention means that the piezoelectric ceramic composition is immersed in a solder bath at 265 ° C. for 10 seconds and then left at room temperature for 24 hours, and the rate of change in oscillation frequency before and after leaving the solder bath for 24 hours. To identify. That is, when the oscillation frequency of the piezoelectric ceramic composition before immersion in the solder bath is F ₁ and the oscillation frequency of the piezoelectric ceramic composition after being left for 24 hours is F ₂ , the heat resistance | ΔF ₀ | is expressed by the following equation (2): Is required.
| ΔF ₀ | = | F ₂ −F ₁ | / F ₁ × 100 (%) (2)

  The remanent polarization (Pr) can be obtained by measuring a polarization-electric field (PE) hysteresis curve. FIG. 1 shows an example of the PE hysteresis curve, and the residual polarization (Pr) is a polarization value when the applied electrolysis is zero. Note that a specific method for obtaining the remanent polarization (Pr) is as described in the column of Examples described later.

When the remanent polarization (Pr) and the heat resistance | ΔF ₀ | were determined for various piezoelectric ceramic compositions, as shown in FIG. 2, there is a correlation between the remanent polarization (Pr) and | ΔF ₀ |. Although this correlation is also shown in FIG. 2, it can be specified by the following equation (3). This indicates that the quality of heat resistance can be determined by the residual polarization (Pr) when a piezoelectric ceramic composition that requires heat resistance is selected.
| ΔF ₀ | = −0.0353 × Pr + 1.1051 (3)

In the present invention, in order to regulate | ΔF ₀ | to 0.3% or less, the residual polarization (Pr) of the piezoelectric ceramic composition is specified based on the above formula (3). That is, the present invention sets the remanent polarization (Pr) in the range of 23.81 to 13.31 μC / cm ² . If the remanent polarization (Pr) is less than 23.81 μC / cm ² , | ΔF ₀ | exceeds 0.3% from the above equation (3). If | ΔF ₀ | is 0%, the remanent polarization (Pr) based on the above equation (3) is 31.31 μC / cm ² , so the upper limit of the remanent polarization (Pr) is 31.31 μC / cm ² . did. A preferable remanent polarization (Pr) is 26.0 μC / cm ² or more, and a more preferable remanent polarization (Pr) is 29.0 μC / cm ² or more.

Although the present invention does not matter how to make the residual polarization (Pr) of the piezoelectric ceramic composition in the range of 23.81 to 13.31 μC / cm ² , the chemical composition of the piezoelectric ceramic composition is adjusted as described below. Thus, the remanent polarization (Pr) can be in the above range.

<Chemical composition>
The composition of the piezoelectric ceramic composition according to the present invention will be described.
The piezoelectric ceramic composition of the present invention includes a perovskite compound containing Pb, Zr, Ti, Mn, and Nb as main components, and has a main component represented by the following formula (1). The chemical composition here refers to the composition after sintering.

Pbα [(Mn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ Formula (1)
In the formula (1), 0.96 ≦ α ≦ 1.01,
0.04 ≦ x ≦ 0.16,
0.48 ≦ y ≦ 0.58,
0.32 ≦ z ≦ 0.42,
x + y + z = 1.
In the formula (1), α, x, y and z each represent a molar ratio.

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 0.96 ≦ α ≦ 1.01. When α is less than 0.96, it is difficult to obtain a dense sintered body. On the other hand, when α exceeds 1.01, the heat resistance deteriorates. Therefore, α is set to a range of 0.96 ≦ α ≦ 1.01. α is preferably 0.97 ≦ α ≦ 1.005, and more preferably 0.98 ≦ α ≦ 1.005.

X indicating the amount of Mn and the amount of Nb is preferably in the range of 0.04 ≦ x ≦ 0.16. When x is less than 0.04, the electrical characteristic Q _max is small. On the other hand, when x exceeds 0.16, good heat resistance cannot be obtained. Therefore, x is in the range of 0.04 ≦ x ≦ 0.16. x is preferably 0.05 ≦ x ≦ 0.14, and more preferably 0.06 ≦ x ≦ 0.11.

  Y indicating the amount of Ti is in a range of 0.48 ≦ y ≦ 0.58. If y is less than 0.48, good heat resistance cannot be obtained. On the other hand, when y exceeds 0.58, it is difficult to obtain good temperature characteristics. Therefore, y is set to a range of 0.48 ≦ y ≦ 0.58. y is preferably 0.49 ≦ y ≦ 0.57, and more preferably 0.50 ≦ y ≦ 0.55.

  Z indicating the amount of Zr is in the range of 0.32 ≦ z ≦ 0.42. If z is less than 0.32 or exceeds 0.42, good temperature characteristics cannot be obtained. Therefore, z is set to a range of 0.32 ≦ z ≦ 0.42. z is preferably 0.33 ≦ z ≦ 0.42, and more preferably 0.34 ≦ z ≦ 0.40.

The piezoelectric ceramic composition according to the present invention having the above main components preferably contains one or two elements selected from Al, Ta, Cr and Sc as subcomponents. These elements are effective elements for making the remanent polarization (Pr) in the range of 23.81 μC / cm ² or more. These elements are also effective in obtaining a piezoelectric ceramic composition having excellent electrical characteristics _Qmax . These elements are 0.01 to 15.0 wt% in terms of oxides of the elements with respect to Pbα [(Mn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ in the formula (1) (however, , Al is 0.20 to 15.0 wt%) , preferably 0.05 to 10.0 wt%, and more preferably 0.20 to 5.0 wt%. The oxides of these elements are Al ₂ O ₃ , Ta ₂ O ₃ , Cr ₂ O ₃ , and Sc ₂ O ₃ . In addition, it is most preferable to use Al as a subcomponent.

The piezoelectric ceramic composition according to the present invention may contain SiO ₂ as an accessory component. SiO ₂ is effective in improving the strength of the sintered body. In the case of adding SiO ₂ , the preferable amount of SiO ₂ is 0.005 to 0.15 wt% with respect to Pbα [(Mn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O _{3 in} the formula (1). The more preferable amount of SiO ₂ is 0.01 to 0.12 wt%, and the more preferable amount of SiO ₂ is 0.01 to 0.10 wt%.

<Manufacturing method>
Next, the preferable 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, Nb ₂ O ₅ powder and the like can be used. Each raw material powder is weighed so as to have the composition of the formula (1).

Next, an oxide powder of one or two elements selected from Al, Ta, Cr, and Sc is added as an auxiliary component to the total weight of each weighed powder in the amount described above. Al ₂ O ₃ , Ta ₂ O ₃ , Cr ₂ O ₃ , Sc ₂ O ₃ powder can be used as the raw material powder of the accessory component. In addition to these subcomponents, when SiO ₂ is contained, a SiO ₂ powder is further prepared. 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 wet mixing the raw material powders of the main component and subcomponent, calcination is carried out for a predetermined time within a range of 700 to 950 ° C. 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 2.0 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 preferable polarization treatment temperature is 60 to 250 ° C, and a more preferable 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 2.0 Ec, the actual voltage becomes high and the sintered body tends to break, making it difficult to produce the piezoelectric ceramic composition. Therefore, the electric field applied during the polarization process is 1.0 to 2.0 Ec. A preferable applied electric field is 1.1 to 1.8 Ec, and a more preferable applied electric field is 1.2 to 1.6 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 preferable polarization treatment time is 0.7 to 20 minutes, and a more preferable 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 desired to be a thickness shear vibration, the polarization direction is set to the direction shown in FIG. The thickness shear vibration is vibration as 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 a piezoelectric element such as a resonator, a filter, a resonator, an actuator, an ignition element, or an ultrasonic motor.

Lead oxide (PbO) powder, titanium oxide (TiO ₂ ) powder, zirconium oxide (ZrO ₂ ) powder, manganese carbonate (MnCO ₃ ) powder, and niobium oxide (Nb ₂ O ₅ ) powder were prepared as starting materials for the main components. . Moreover, the oxide powder shown in the column of the subcomponent of Table 1 and Table 2 was prepared as a starting material of a subcomponent. Further, SiO ₂ powder was also prepared as a raw material for other subcomponents. These raw material powders were weighed so as to have the compositions shown in Tables 1 and 2, and wet-mixed for 10 hours in pure water using a ball mill (using ZrO ₂ balls). The amount of SiO ₂ powder added was constant at 0.02 wt%. The obtained slurry was sufficiently dried and then press-molded. Thereafter, calcination was performed in the air at 800 to 950 ° C. for 2 hours. After finely pulverizing with a ball mill until the calcined body had an average particle size of 0.7 μm, the finely pulverized powder was dried. An appropriate amount of PVA (polyvinyl alcohol) as a binder was added to the dried finely pulverized powder and granulated. The granulated powder was inserted into a 20 mm × 20 mm mold of a uniaxial press molding machine and then molded at a pressure of 245 MPa. After the binder removal treatment was performed on the obtained molded body, sintering was performed in air at 1150 to 1250 ° C. for 2 hours to obtain a sintered body (sample).

Residual polarization (Pr) of the sintered body obtained above was measured as follows.
The front and back surfaces of the sintered body were flattened to a thickness of 0.35 mm with a lapping machine, and then cut into dimensions of 6 mm length × 6 mm width × 0.35 mm thickness with a dicing saw. Thereafter, Ag electrodes were formed on both the front and back surfaces of this sample by vacuum vapor deposition to obtain a residual polarization (Pr) measurement sample.
An electric field was applied to the obtained sample in a silicone oil bath at 150 ° C. by RT-6000HVS manufactured by Radiant Technology, and a PE hysteresis curve was measured. Based on this PE hysteresis curve, the remanent polarization (Pr) of each sample was determined. The results are shown in Table 1. The applied electric field is the coercive electric field Ec of the average value of Ec1 and Ec2, where Ec1 is the positive coercive field of the PE hysteresis curve, and Ec2 is the absolute value of the negative coercive field. The electric field was 2 to 3 times Ec.

Next, the electrical characteristics Q _max of the sintered body obtained above were measured as follows.
After flattening both sides of the sample to a thickness of 0.5 mm with a lapping machine, cut with a dicing saw to 15 mm long × 5.0 mm wide to form temporary electrodes for polarization at both ends (5.0 mm direction) did. Thereafter, a polarization treatment was performed by applying an electric field of 3 kV / mm for 15 minutes in a silicon oil bath at a temperature of 150 ° C. The polarization direction was the direction shown in FIG. Thereafter, the temporary electrode was removed. In addition, the size of the sample after removal of the temporary electrode is 15 mm long × 4.0 mm wide × 0.5 mm thick. The thickness was again polished to about 0.3 mm with a lapping machine, and the vibrating electrodes 2 were formed on both the front and back surfaces (polished surfaces) of the test piece 1 as shown in FIG. 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. The overlap of the vibrating electrode 2 was 1.5 mm.

Subsequently, a piezoelectric element having a length of 4 mm, a width of 0.7 mm, and a thickness of 0.3 mm was cut out from the above test piece 1 to obtain a sample for measuring the electrical characteristics _Qmax . The electrical characteristic Q _max was measured using an impedance analyzer (4294A manufactured by Agilent Technologies) at around 4 MHz. The results are shown in Table 1. The electric characteristic Q _max represents the maximum value of Q (= tan θ, θ: phase angle (deg)) between the resonance frequency fr and the anti-resonance frequency fa, and is one of important characteristics as a resonator. Larger _max contributes to low voltage driving.

From Tables 1 and 2, sample Nos. Included in 23.13 to 31.95 μC / cm ² whose remanent polarization (Pr) is within the scope of the present invention. 12, 19 and 53 show that | ΔF ₀ | has excellent heat resistance of 0.3% or less. These samples 12,19,53 are electrical characteristics Q _max is achieved a more than 145 values, show excellent values in both heat resistance and electrical properties.

A piezoelectric ceramic composition (sintered body) having the composition shown in Table 3 was prepared in the same manner as in Example 1 as the main component raw material powder and subcomponent raw material powder similar to Example 1. With respect to the obtained sintered body, the remanent polarization (Pr), the heat resistance | ΔF ₀ |, and the electrical property Q _max were measured in the same manner as in Example 1. The results are shown in Table 3.

From Table 3, the remanent polarization (Pr) varies depending on the value of α in the formula (1) indicating the composition of the main component, and when Al ₂ O ₃ is used as a subcomponent, a peak exists in the remanent polarization (Pr). I understand that

Al ₂ O ₃ was prepared as the main component raw material powder and subcomponent raw material powder as in Example 1, and a piezoelectric ceramic composition (sintered body) having the composition shown in Table 4 was prepared in the same manner as in Example 1. . With respect to the obtained sintered body, the remanent polarization (Pr), the heat resistance | ΔF ₀ |, and the electrical property Q _max were measured in the same manner as in Example 1. The results are shown in Table 4.

From Table 4, when Al ₂ O ₃ is used as the subcomponent, the remanent polarization (Pr) is in the range of 26 to 28 μC / cm ² , and the heat resistance | ΔF ₀ | is extremely low at 0.1% or less. The value can be regulated. In addition, the piezoelectric ceramic composition using Al ₂ O ₃ as the accessory component has a high electric characteristic Q _{max of} 120 or more.

Al ₂ O ₃ was prepared as the main component raw material powder and subcomponent raw material powder as in Example 1, and a sintered body sample as a piezoelectric ceramic composition was prepared in the same manner as in Example 1. With respect to the obtained sintered body, the remanent polarization (Pr), the heat resistance | ΔF ₀ |, and the electrical property Q _max were measured in the same manner as in Example 1. The results are shown in Table 5.

From Table 5, x in the formula (1) representing the composition of the main component, the y and z be varied within the scope of the present invention, in the residual polarization (Pr) is in the range of the present invention | [Delta] F ₀ Has an excellent heat resistance of 0.1% or less, and an electric characteristic Q _max exceeding 150 is also obtained, confirming that a piezoelectric ceramic composition excellent in heat resistance and electric characteristic Q _max can be obtained. did it.

It is a figure which shows the example of a PE hysteresis curve. It is a graph which shows the relationship between remanent polarization (Pr) and heat resistance | ΔF ₀ |. It is a figure for demonstrating the polarization direction. It is sectional drawing of the test piece in the state in which the vibration electrode was formed in upper and lower surfaces.

Explanation of symbols

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

Claims (2)

Pbα [(Mn _1/3 Nb _2/3 ) _x Ti _y Zr _z ] O ₃ Formula (1)
(In formula (1), 0.96 ≦ α ≦ 1.01,
0.04 ≦ x ≦ 0.16,
0.48 ≦ y ≦ 0.58,
0.32 ≦ z ≦ 0.42,
x + y + z = 1.
In the formula (1), α, x, y and z each represent a molar ratio. Have a main component represented by), Al as the minor component, Ta, at least one element selected from Cr and Sc, 0.01~15.0wt% in terms of oxide of each element (however, Al Is composed of a sintered body containing 0.20 to 15.0 wt%) ,
A piezoelectric ceramic composition having a remanent polarization at 150 ° C. of 23.81 to 13.31 μC / cm ² . The piezoelectric ceramic composition according to claim 1, wherein 0.98 ≦ α ≦ 1.005 in the formula (1).

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