JP2001181037A - Piezoelectric porcelain composition and piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a piezoelectric porcelain composition capable of being fired at a temperature of <1,150 deg.C, having a large mechanical quality factor and having small deterioration of the mechanical quality factor in high electric field driving and a piezoelectric transformer using the piezoelectric porcelain composition. SOLUTION: This piezoelectric porcelain composition is obtained by including a composition represented by the composition formula: (PbuA1-u)u[(Zn1/3 Nb2/3)xTiyZrz]2-vO3 (wherein, A is at least one kind of element selected from the group composed of La, Nd, Pr and Bi; and (u), (v), (x), (y) and (z) satisfy reflectively 0.92<=u<=0.99, 0.97<=v<=1.03, 0.06<=x<=0.18, 0.43<=y<=0.53, 0.29<=z<=0.51 and x+y+z=1) and adding Mn in an amount of 0.7-3 mol% expressed in terms of MnO2 based on the composition, Al in an amount of 0.7-2.4 mol% expressed in terms of Al2O3 based on the composition and Si in an amount of 0.1-1.5 mol% expressed in terms of SiO2 based on the composition to the composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition suitable for, for example, an ultrasonic vibrator, an actuator, a piezoelectric transformer, and the like, and a piezoelectric transformer using the piezoelectric ceramic composition.

[0002]

2. Description of the Related Art Various devices using piezoelectric materials, such as ultrasonic vibrators, actuators and piezoelectric transformers, have been developed. For example, a piezoelectric transformer is a device that converts input electric energy into mechanical vibration energy in a driving unit and converts it into electric energy again in a power generation unit to increase or decrease the input voltage. With the miniaturization of, they have begun to be applied to inverters for cold cathode tubes used as backlights of liquid crystal displays.

A piezoelectric material applied to such a piezoelectric device is a material that converts electric energy into mechanical vibration energy or mechanical vibration energy into electric energy, and has a large electromechanical coupling coefficient and mechanical quality. It is required to have a coefficient. As an example of the piezoelectric material, Pb (Zn _1/3 Nb _2/3 ) O ₃ -Pb (Sn
There is a piezoelectric ceramic composition in which MnO ₂ is added to a _1/3 Nb _2/3 ) O ₃ —PbTiO ₃ —PbZrO ₃ composition, and it has been revealed that the composition exhibits excellent piezoelectricity (Japanese Patent Publication No. 56-56). 3
0714).

[0004]

In recent years, a piezoelectric device has been required to be driven at a high electric field in response to a demand for higher output. However, although the conventional piezoelectric ceramic composition shows relatively excellent piezoelectricity in low electric field driving,
In high electric field driving, the mechanical quality factor is significantly reduced. Therefore, there is a problem in that when driving in a high electric field, there is a possibility that heat is rapidly generated due to internal energy loss.

In addition, the conventional piezoelectric ceramic composition has a high firing temperature, and it is difficult to fire simultaneously with an electrode material such as a silver-palladium paste when manufacturing a piezoelectric device having a laminated structure.

[0006] In addition, a piezoelectric transformer using a piezoelectric ceramic composition is required to be small and thin with the downsizing of electronic devices. Furthermore, if the driving frequency is high, the conversion efficiency of the entire circuit may be reduced due to the influence of stray capacitance around the circuit including the piezoelectric transformer, and therefore it is required that the circuit can be driven by a low-frequency AC electric signal. ing. However, the conventional piezoelectric transformer using the piezoelectric ceramic composition has a problem that the conversion efficiency of the piezoelectric transformer itself is significantly reduced due to the reduction in size and thickness of the piezoelectric body and the reduction in the driving frequency.

The present invention is a piezoelectric ceramic composition which can be fired at a relatively low temperature, has a large mechanical quality factor, and has a small decrease in the mechanical quality factor under high electric field driving. It is an object of the present invention to provide a piezoelectric ceramic composition capable of ensuring a sufficiently high conversion efficiency when applied to a piezoelectric ceramic, and a piezoelectric transformer using the piezoelectric ceramic composition.

[0008]

Means for Solving the Problems To achieve the above object, a first piezoelectric ceramic composition of the present invention comprises a composition represented by the following composition formula (I) and Mn converted to MnO _2. and 0.7 to 3 mol% with respect to the composition Te, the Al Al ₂
And 0.7 to 2.4 mol% relative to the composition in terms of O _3, relative to the composition in terms of Si to SiO ₂ containing 0.1 to 1.5 mol% It is characterized by the following.

[0009] _{(Pb u A 1-u)} v {(Zn 1/3 Nb 2/3) x Ti y Zr z} 2-v O 3 (I) where, in the above composition formula (I), A La , Nd, P
r and Bi are at least one element selected from the group consisting of r and Bi, and u and v are each 0.92 ≦ u ≦ 0.
99, 0.97 ≦ v ≦ 1.03, and x, y and z
Are respectively 0.06 ≦ x ≦ 0.18 and 0.43 ≦ y ≦
0.53, 0.29 ≦ z ≦ 0.51, and x +
The relationship of y + z = 1 is satisfied.

By adopting such a constitution, a piezoelectric ceramic composition which can be fired at a relatively low temperature, has a large mechanical quality factor, and has a small decrease in the mechanical quality factor under high electric field driving. It can be. Further, a piezoelectric ceramic composition capable of securing a sufficiently high conversion efficiency when applied to a piezoelectric transformer can be obtained.

In order to achieve the above object, a second piezoelectric ceramic composition according to the present invention comprises a composition represented by the following composition formula (II) and the above composition obtained by converting Al to Al ₂ O ₃ . And 0.7 to 2.4 mol% with respect to the composition, and 0.1 to 1.5 mol% with respect to the composition when Si is converted to SiO ₂ .

[0012] _{t (Pb u A 1-u} ) v [(Zn 1/3 Nb 2/3) x Ti y Zr z] 2-v O 3 - (1-t) YMnO 3 (II) where the composition In the formula (II), A is La, Nd, P
at least one element selected from the group consisting of r and Bi, wherein t, u and v are each 0.970 ≦ t
≤ 0.994, 0.92 ≤ u ≤ 0.99, 0.97 ≤ v
≦ 1.03, and x, y and z are each 0.06
≦ x ≦ 0.18, 0.43 ≦ y ≦ 0.53, 0.29 ≦
z ≦ 0.51 and the relationship x + y + z = 1 is satisfied.

With such a configuration, a piezoelectric ceramic composition which can be fired at a relatively low temperature, has a large mechanical quality factor, and has a small decrease in the mechanical quality factor when driven by a high electric field. It can be. Further, a piezoelectric ceramic composition capable of securing a sufficiently high conversion efficiency when applied to a piezoelectric transformer can be obtained.

In order to achieve the above object, a piezoelectric transformer according to the present invention is characterized in that the piezoelectric transformer contains the first piezoelectric ceramic composition or the second piezoelectric ceramic composition. With such a configuration, a sufficiently high conversion efficiency can be ensured even when the size and thickness are reduced and the driving frequency is reduced. In general, output voltage control tends to be difficult with miniaturization. However, according to the piezoelectric transformer of the present invention, the capacitance of the power generation unit can be made relatively small. Even in this case, the output voltage can be controlled relatively easily.

In the piezoelectric transformer, it is preferable that the piezoelectric transformer includes a piezoelectric body composed of a piezoelectric ceramic composition, and the piezoelectric body has a lengthwise polarization part and a thickness direction polarization part. Here, the “thickness direction” is a direction of the thickness of the plate-shaped piezoelectric body, and the “length direction” is a direction orthogonal to the thickness direction.

In the piezoelectric transformer, the piezoelectric body includes a first longitudinally polarized portion and a second longitudinally polarized portion which are separated from each other, and the thickness directionally polarized portion includes the first longitudinally polarized portion. Preferably, it exists between the vertical polarization part and the second longitudinal polarization part. According to this preferred example, it is possible to lower the drive frequency while ensuring a sufficiently high conversion efficiency.

In the piezoelectric transformer, the piezoelectric body preferably excites a fundamental vibration mode. According to this preferred example, it is possible to lower the drive frequency while ensuring a sufficiently high conversion efficiency.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the first piezoelectric ceramic composition of the present invention is obtained by adding Mn, Al and Si to the composition represented by the composition formula (I).

[0019] In _{(Pb u A 1-u)} v {(Zn 1/3 Nb 2/3) x Ti y Zr z} 2-v O 3 (I) a composition formula (I), A is La, Nd, Pr and B
i is at least one element selected from the group consisting of i.

U is in the range of 0.92 to 0.99.
If the ratio is outside the above range, a sufficient mechanical quality factor cannot be obtained. Further, it is preferable that 0.92 ≦ u ≦ 0.96. Also, v is in the range of 0.97 to 1.03. If the ratio is outside the above range, a sufficient mechanical quality factor cannot be obtained.

X is in the range of 0.06 to 0.18.
If the ratio is outside the above range, a sufficient mechanical quality factor cannot be obtained. Further, it is preferable that 0.125 ≦ x ≦ 0.18. y is in the range of 0.43 to 0.53. If the ratio is outside the above range, a sufficient mechanical quality factor cannot be obtained. z is in the range of 0.29 to 0.51. If the ratio is outside the above range, a sufficient mechanical quality factor cannot be obtained. Further, x, y and z are x + y + z
= 1 is satisfied.

Mn is added at a ratio of 0.7 to 3 mol% with respect to the composition represented by the composition formula (I) in terms of MnO ₂ . If the ratio is outside the above range, a sufficient mechanical quality factor cannot be obtained. In particular, Mn is MnO ₂
It is preferable to add 1.9 to 3 mol% with respect to the composition in terms of the composition. Mn is Mn ₂
O ₃ and MnCO ₃ are preferably added to the composition.

Al is converted to Al ₂ O _3, and is 0.7 to 2.4 mol% based on the composition represented by the composition formula (I).
At a rate of If the ratio is outside the above range, a sufficient mechanical quality factor cannot be obtained. Al is Al
Preferably, it is added to the composition as ₂ O ₃ .

Si is 0.1 to 1.5 mol% in terms of SiO ₂ with respect to the composition represented by the composition formula (I).
At a rate of If the ratio is outside the above range, a sufficient mechanical quality factor cannot be obtained. Si is Si
Preferably, it is added to the composition as O ₂ .

As described above, the second piezoelectric ceramic composition of the present invention contains Al and S in the composition represented by the composition formula (II).
i is added.

[0026] _{t (Pb u A 1-u} ) v [(Zn 1/3 Nb 2/3) x Ti y Zr z] 2-v O 3 - (1-t) YMnO 3 (II) where the composition In the formula (II), A is La, Nd, P
at least one element selected from the group consisting of r and Bi, wherein t, u and v are each 0.970 ≦ t
≤ 0.994, 0.92 ≤ u ≤ 0.99, 0.97 ≤ v
≦ 1.03, and x, y and z are each 0.06
≦ x ≦ 0.18, 0.43 ≦ y ≦ 0.53, 0.29 ≦
z ≦ 0.51 and the relationship x + y + z = 1 is satisfied.

Here, the reason for setting 0.970 ≦ t ≦ 0.994 is that a sufficient mechanical quality factor cannot be obtained if the value is outside the above range. Furthermore, 0.98 ≦ t ≦ 0.99
4 is particularly preferred.

The composition represented by the composition formula (II) is as follows:
It is obtained by adding Mn as YMnO ₃ to the composition represented by the composition formula (I). Therefore, u, y, v, x, y
The ranges of z and z are set to be the same as in the first piezoelectric ceramic composition for the same reason as described above. Also, A
The addition ratios of 1 and Si can be the same as in the first piezoelectric ceramic composition described above.

The piezoelectric ceramic composition according to the present invention can be applied to all piezoelectric devices such as a piezoelectric transformer, an ultrasonic transducer, and an actuator.

The piezoelectric ceramic composition of the present invention can be fired at a relatively low temperature, specifically, at less than 1150 ° C. by having the above composition. Furthermore, a large mechanical quality factor can be realized, and a decrease in the mechanical quality factor during high electric field driving can be suppressed.

Further, by applying the piezoelectric ceramic composition of the present invention, it is possible to reduce the thickness and the size of the piezoelectric device while ensuring sufficient characteristics of the piezoelectric device. Also,
Since the piezoelectric ceramic composition can be fired at a relatively low temperature, it can be fired at the same time as the electrode material during its production, and is suitable for application to a piezoelectric device having a laminated structure.

Next, the piezoelectric transformer of the present invention will be described.

The piezoelectric transformer of the present invention is constituted by using the piezoelectric ceramic composition of the present invention as described above. FIG.
It is a perspective view showing an example of a piezoelectric transformer concerning the present invention.
Note that, in FIG. 1, arrows indicate the polarization direction of the piezoelectric body.

This piezoelectric transformer includes a piezoelectric body 1 including a piezoelectric body driving section 1a and a piezoelectric body power generation section 1b, input electrodes 2a and 2b, and an output electrode 3.

The piezoelectric body 1 is composed of the first or second piezoelectric ceramic composition of the present invention. The piezoelectric body is not particularly limited, but usually has a plate shape.

In the piezoelectric body driving section 1a, input electrodes 2a and 2b are formed on two main surfaces (hereinafter, referred to as "upper surface" and "lower surface") of the piezoelectric body 1, respectively.
This is a portion where the piezoelectric body 1 is sandwiched in the thickness direction by the input electrodes 2a and 2b. The piezoelectric body driving section 1a is processed so as to be polarized in the thickness direction between the input electrodes 2a and 2b.

The piezoelectric power generating section 1b is a portion of the piezoelectric body 1 adjacent to the piezoelectric driving section 1a, and the output electrode 3 is provided on the upper surface (or lower surface) of the end opposite to the piezoelectric driving section 1a. Is formed. The piezoelectric power generation unit 1b is processed so as to be polarized in the length direction between the input electrodes 2a and 2b and the output electrode 3.

Next, the operation of the piezoelectric transformer shown in FIG. 1 will be described. When an AC electric signal is applied between the input electrodes 2a and 2b, mechanical vibration due to the inverse piezoelectric effect is excited in the piezoelectric body driving section 1a. Due to this mechanical vibration, an electric field is generated by the piezoelectric effect in the piezoelectric power generation unit 1b, and a voltage is generated between the input electrodes 2a and 2b and the output electrode 3. By extracting this voltage as an electric signal, the input voltage is converted to an output voltage. The relationship between the input voltage and the output voltage depends on the dimensions of the piezoelectric body 1, the frequency of the applied AC electric signal, and the like.

In this piezoelectric transformer, when the secondary vibration mode of the longitudinal stretching vibration of the piezoelectric body 1 is excited,
Voltage conversion is performed most efficiently. Therefore, it is preferable to drive the piezoelectric transformer with an AC electric signal having a frequency that causes resonance in the secondary vibration mode of the longitudinal stretching vibration.

Further, the piezoelectric transformer can be driven by an AC electric signal having a frequency that causes resonance in a fundamental vibration mode of longitudinal stretching vibration. in this case,
The driving frequency can be reduced to 比 べ compared with the case where the secondary vibration mode is resonated.

FIG. 2 is a perspective view showing another example of the piezoelectric transformer according to the present invention. Note that, in FIG. 2, arrows indicate the polarization direction of the piezoelectric body.

The piezoelectric transformer includes a piezoelectric body 4 including a piezoelectric body driving section 4a and piezoelectric body power generation sections 4b and 4c.
, Input electrodes 5a and 5b, output electrodes 6a and 6b,
6c and 6d.

The piezoelectric body 4 is composed of the first or second piezoelectric ceramic composition of the present invention. The piezoelectric body is not particularly limited, but usually has a plate shape.

The piezoelectric body driving section 4a has input electrodes 5a and 5b formed on the upper and lower surfaces of the piezoelectric body 4, respectively.
This is a portion where the piezoelectric body 4 is sandwiched in the thickness direction by the input electrodes 5a and 5b. The piezoelectric body driving section 4a is processed so as to be polarized in the thickness direction between the input electrodes 5a and 5b.

The piezoelectric power generating sections 4b and 4c are portions of the piezoelectric body 4 adjacent to the piezoelectric driving section 4a, respectively, on the upper and lower surfaces of the end opposite to the piezoelectric driving section 4a.
Output electrodes 6a and 6b, 6c and 6d are formed respectively. The piezoelectric power generation unit 4b includes input electrodes 5a and 5
b and the output electrodes 6a and 6b are processed so as to be polarized in the length direction. Similarly, the piezoelectric power generation unit 4c is processed so as to be polarized in the length direction between the input electrodes 5a and 5b and the output electrodes 6c and 6d.

The piezoelectric driving section 4a is disposed near the center of the piezoelectric element 4, the piezoelectric power generating section 4b is disposed near one end of the piezoelectric substance 4, and the piezoelectric power generating section 4c is connected to the other side of the piezoelectric substance 4. It is arranged near the end of. That is, the piezoelectric power generating units 4b and 4c are respectively disposed on both sides of the piezoelectric driving unit 4a.

Next, the operation of the piezoelectric transformer will be described. When an AC electric signal is applied between the input electrodes 5a and 5b, mechanical vibration due to the inverse piezoelectric effect is excited in the piezoelectric body driving unit 4a. Due to this mechanical vibration, an electric field is generated by the piezoelectric effect in the piezoelectric power generation unit 4b, and a voltage is generated between the input electrodes 5a and 5b and the output electrodes 6a and 6b. Similarly, an electric field is generated by the piezoelectric effect in the piezoelectric power generation unit 4c, and a voltage is generated between the input electrodes 5a and 5b and the output electrodes 6c and 6d. By extracting these voltages as electrical signals,
The input voltage is converted to an output voltage. The relationship between the input voltage and the output voltage depends on the size of the piezoelectric body 4, the frequency of the applied AC electric signal, and the like.

In this piezoelectric transformer, when the fundamental vibration mode of the longitudinal expansion and contraction vibration of the piezoelectric body 4 is excited,
Voltage conversion is performed most efficiently. Therefore, it is preferable that the piezoelectric transformer be driven by an AC electric signal having a frequency that causes resonance in the fundamental vibration mode of the longitudinal stretching vibration.

By using the piezoelectric ceramic composition of the present invention, a sufficiently high conversion efficiency can be ensured in the piezoelectric transformer of the present invention even when the size and thickness of the piezoelectric transformer are reduced and the driving frequency is reduced. Further, since the capacitance of the power generation unit can be made relatively small, the output voltage can be controlled relatively easily even when the size is reduced.

[0050]

(Example 1) Chemically high-purity P as a raw material
bO, La ₂ O ₃ , Nd ₂ O ₃ , Pr ₂ O ₃ , Bi ₂ O ₃ , Zn
O, Nb ₂ O ₅ , TiO ₂ , ZrO ₂ , MnCO ₃ , Al ₂ O
₃ , SiO ₂ and Y ₂ O ₃ were weighed so as to have a predetermined composition, and were wet-mixed by a ball mill using zirconia balls. The mixture was taken out of the ball mill and dried, and then calcined in the air at 850 to 1000 ° C. for 2 hours. The calcined powder was wet-pulverized by a ball mill using zirconia balls, the pulverized slurry was taken out from the ball mill, dried, and granulated by adding a polyvinyl alcohol solution. The obtained granulated powder was formed into a disk having a diameter of 20 mm and a thickness of about 2 mm using a mold and a press. After the molded body was held in air at 700 ° C. for 1 hour to remove the binder, it was heated in air at 100 ° C.
It baked by holding at 0-1260 degreeC for 2 hours. After processing the fired body into a disk having a diameter of about 16 mm and a thickness of about 1 mm, silver electrodes were baked on the upper and lower surfaces thereof. A DC electric field of 1 to 5 kV / mm was applied to the device in an insulating oil at 100 ° C. to perform a polarization treatment.

By the above operation, 52 types of samples (sample numbers 1 to 52) having different compositions were prepared. For each sample,
The mechanical quality factor (Qm value) of the disk radial vibration was calculated from the measurement by the resonance anti-resonance method using the impedance analyzer. The Qm value was determined for each of the cases where the applied voltage was 0.1 Vrms and 5 Vrms.

The results are shown in Tables 1 and 2 together with the composition and firing temperature of each sample. The coefficients (u, v, x, y, z) and element (A) in Table 1 are in accordance with the composition formula (I), and the coefficients (t, u, v, x, y,
z) and the element (A) are in accordance with the composition formula (II). In addition, the display of mol% of Mn, Al and Si is as follows.
The ratios (mol%) with respect to the composition represented by the composition formula (I) or (II) in terms of MnO ₂ , Al ₂ O ₃ and SiO ₂ are shown. In addition, (*) written on the right side of the sample number indicates that the sample was prepared as a comparative example outside the scope of the present invention.

[0053]

[Table 1]

[0054]

[Table 2]

As shown in Tables 1 and 2, the sample according to the embodiment of the present invention was driven at a low electric field (driving voltage 0.1 Vrm).
s) shows a high Qm value of 1800 or more, and
1500 even at high electric field driving (driving voltage 5Vrms)
It was confirmed that a high Qm value as described above was exhibited.

In particular, as shown in Table 2, the composition formula (I
In the example in which Al and Si were added to the composition represented by I), the Qm value was 1900 or more at the time of low electric field driving,
In addition, it exhibited a high value of 1700 or more during high electric field driving.

Furthermore, in the sample of the example, this high Qm value could be realized at a relatively low firing temperature of less than 1150 ° C.

On the other hand, it was confirmed that the sample of the comparative example had a low Qm value, and was extremely low particularly when driven by a high electric field.

(Example 2) A granulated powder obtained in the same manner as in Example 1 was weighed to a length of 50 mm and a width of 1 using a mold and a press.
It was formed into a rectangular plate having a thickness of 0 mm and a thickness of about 3 mm. After the molded body was held in air at 700 ° C. for 1 hour to remove the binder, it was held in air at 1000 to 1260 ° C. for 2 hours and fired to obtain a fired body.

A piezoelectric transformer having a structure similar to that of FIG. 1 was manufactured using the fired body. First, make the fired body 3
It was processed into a rectangular plate of 9 mm, width 8 mm, thickness 1.8 mm or 0.9 mm. In a portion corresponding to the piezoelectric body driving unit, after silver and palladium pastes were baked on the upper and lower surfaces of the fired body to form input electrodes, polarization processing was performed between the input electrodes in the thickness direction. In addition, in a portion corresponding to the piezoelectric power generation unit, after baking silver-palladium paste on the upper surface of the fired body to form an output electrode having a width of 1 mm, polarization processing is performed in the length direction between the input electrode and the output electrode. gave. In addition, the length of the piezoelectric body drive unit and the piezoelectric body power generation unit are respectively
It was 19.5 mm.

By the above operation, 28 kinds of piezoelectric transformers (sample numbers 53 to 80) were produced, and a load resistance of 120 kΩ was connected to the output electrode. For each sample, an AC electric signal was applied between the input electrodes to determine the conversion efficiency. The conversion efficiency [%] is a value represented by P _out / P _in × 100 when the input power is P _in and the output power is P _out .

The conversion efficiency depends on whether the driving is performed with an AC electric signal having a frequency (80 kHz) that resonates the secondary vibration mode of the longitudinal stretching vibration, or the frequency (40 kHz) that resonates the fundamental vibration mode. Each case of driving by an electric signal was evaluated. Note that the input power P
_in was 3 W.

The results are shown in Tables 3 and 4 together with the composition and thickness of the piezoelectric material of each sample. The coefficients (u, v, x, y, z) and element (A) in Table 3 are in accordance with the composition formula (I), and the coefficients (t, u, v, x, y,
z) and the element (A) are in accordance with the composition formula (II). In addition, the display of mol% of Mn, Al and Si is as follows.
The ratios (mol%) with respect to the composition represented by the composition formula (I) or (II) in terms of MnO ₂ , Al ₂ O ₃ and SiO ₂ are shown. In addition, (*) written on the right side of the sample number indicates that the sample was prepared as a comparative example outside the scope of the present invention.

[0064]

[Table 3]

[0065]

[Table 4]

As shown in Tables 3 and 4, the sample according to the embodiment of the present invention has a drive for exciting the secondary vibration mode,
That is, in high-frequency driving, a high conversion efficiency of 87% or more was exhibited even when the piezoelectric body was as thin as 0.9 mm. In addition, a high conversion efficiency of 83% or more was exhibited even in driving for exciting the fundamental vibration mode, that is, in low-frequency driving.

In particular, as shown in Table 4, the composition formula (I
Examples in which Al and Si were added to the composition represented by I) exhibited high conversion efficiencies of 90% in high-frequency driving and 86% or more in low-frequency driving.

Furthermore, the sample of the example was able to realize this high conversion efficiency at a relatively low firing temperature of less than 1150 ° C. From this, it was found that by using the piezoelectric ceramic composition having the same composition as that of the sample of the example, it is possible to manufacture a laminated piezoelectric transformer by firing simultaneously with the silver palladium paste. Actually, using a piezoelectric ceramic composition having the same composition as that of Sample Nos. 58 and 70, a laminated piezoelectric transformer in which nine piezoelectric ceramic composition layers and ten silver palladium electrode layers are alternately laminated. Was manufactured and its characteristics were evaluated. As a result, it was confirmed that the device exhibited high conversion efficiency and a high step-up ratio.

On the other hand, it was confirmed that the conversion efficiency of the sample of the comparative example was low, especially when the piezoelectric body was as thin as 0.9 mm. Also, it was confirmed that the conversion efficiency was significantly reduced even when driving at a low frequency.

(Embodiment 3) The granulated powder obtained in the same manner as in Embodiment 1 was weighed to a length of 50 mm and a width of 1 using a mold and a press.
It was formed into a rectangular plate having a thickness of 0 mm and a thickness of about 3 mm. After the molded body was held in air at 700 ° C. for 1 hour to remove the binder, it was held in air at 1000 to 1260 ° C. for 2 hours and fired to obtain a fired body.

Using the fired body, a piezoelectric transformer having the same structure as that of FIG. 2 was manufactured. First, make the fired body 3
It was processed into a rectangular plate having a width of 9 mm, a thickness of 8 mm, and a thickness of 0.9 mm. In the portion corresponding to the piezoelectric body driving section, after the input electrodes were formed on the upper and lower surfaces of the fired body by silver baking, polarization processing was performed between the input electrodes in the thickness direction. In addition, in a portion corresponding to the piezoelectric power generation unit, a silver-palladium paste is baked on the upper and lower surfaces of the fired body to form an output electrode having a width of 1 mm. Was given. The length of the piezoelectric body driving section was 23 mm, and the length of the piezoelectric body power generation section was 8 mm.

With the above operation, 14 kinds of piezoelectric transformers (sample numbers 81 to 94) were produced, four leads were connected to a load resistance of 120 kΩ, and each lead was connected to each output electrode. For each sample, an AC electric signal was applied between the input electrodes to evaluate the conversion efficiency. The conversion efficiency is P _out / P _in × 1 when the input power is P _in and the output power is P _out.
It is a value represented by 00.

The conversion efficiency was evaluated by driving with an AC electric signal having a frequency (40 kHz) that resonates the fundamental vibration mode of longitudinal stretching vibration. The input power is 3W
And

The results are shown in Tables 5 and 6, together with the composition and firing temperature of the piezoelectric material of each sample. The coefficients (u, v, x, y, z) and element (A) in Table 5 are in accordance with the composition formula (I), and the coefficients (t, u, v, x,
y, z) and the element (A) are in accordance with the composition formula (II). In addition, the expression of mol% of Mn, Al and Si means the ratio (mol) of the composition represented by the composition formula (I) or (II) in terms of MnO ₂ , Al ₂ O ₃ and SiO ₂ respectively. %). In addition, (*) written on the right side of the sample number indicates that the sample was prepared as a comparative example outside the scope of the present invention.

[0075]

[Table 5]

[0076]

[Table 6]

The resonance frequency of the longitudinal stretching vibration of the piezoelectric body differs depending on the vibration mode and depends on the length of the piezoelectric body. When the resonance frequency is 40 kHz, the length of the piezoelectric body is set to about 80 mm when excited in the secondary vibration mode, and the length of the piezoelectric body is about 40 mm when excited in the fundamental vibration mode.
Must be set to That is, in order to realize a small-sized piezoelectric transformer, it is effective to excite the piezoelectric body in the fundamental vibration mode. However, as described above, when excitation is performed in the basic vibration mode, the driving frequency is reduced, and the conversion efficiency of the piezoelectric transformer tends to decrease.

However, as shown in Tables 5 and 6, according to the sample of this embodiment, the driving frequency was 40 k
Even when driving at a low frequency of Hz, 86
%. From this, it was confirmed that the sample according to the present example can be driven at a low frequency, that is, excited in the fundamental vibration mode, while ensuring high conversion efficiency.

On the other hand, the sample of the comparative example had a remarkably low conversion efficiency in low frequency driving.

Further, from the comparison between Table 3 and Table 5, it was confirmed that the piezoelectric transformer having the structure shown in FIG. 2 exhibited higher conversion efficiency than the piezoelectric transformer having the structure shown in FIG. .

However, when the external shape is the same, the capacitance of the power generation unit of the piezoelectric transformer is about four times larger in the configuration of FIG. 2 than in the configuration of FIG. It is considered to be. Actually, when the samples of the comparative examples (sample numbers 81, 87, 88, and 94) were mounted on a 3 W cold-cathode tube inverter and subjected to a lighting test, an unstable operation of repeating lighting and extinguishing was shown.

On the other hand, in the sample according to the present example, it was confirmed that the capacitance of the power generation unit was relatively small, and was about ３ to ／ of the sample of the comparative example. Actually, the samples according to the present example (sample numbers 82 to 86, 89
To 93), a lighting test of the cold cathode tube was similarly performed, and stable operation was shown.

[0083]

As described above, the piezoelectric ceramic composition of the present invention can be fired at a relatively low temperature, has a large mechanical quality factor, and has a high mechanical strength under high electric field driving. A piezoelectric ceramic composition with a small decrease in quality factor can be obtained. Furthermore, according to the piezoelectric ceramic composition of the present invention,
When applied to a piezoelectric transformer, it is possible to ensure a sufficiently high conversion efficiency.

According to the piezoelectric transformer of the present invention, a sufficiently high conversion efficiency can be ensured even when the size and thickness are reduced and the driving frequency is reduced.

[Brief description of the drawings]

FIG. 1 is a perspective view showing an example of a piezoelectric transformer according to the present invention.

FIG. 2 is a perspective view showing another example of the piezoelectric transformer according to the present invention.

[Explanation of symbols]

 1, 4 Piezoelectric body 1a, 4a Piezoelectric body driving section 1b, 4b, 4c Piezoelectric power generation section 2a, 2b, 5a, 5b Input electrode 3, 6a, 6b, 6c, 6d Output electrode

Continuing from the front page (72) Inventor Masamitsu Nishida 1006 Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. Person Hiroyuki Hase 1006 Kazuma Kadoma, Kadoma City, Osaka Prefecture F-term in Matsushita Electric Industrial Co., Ltd. (reference) 4G031 AA07 AA09 AA11 AA12 AA14 AA19 AA26 AA29 AA30 AA32 AA35 BA10

Claims (6)

[Claims] 1. A composition represented by the following composition formula (I), wherein Mn is converted to MnO ₂ and the composition is added to the composition in an amount of 0.1 to 0.1%.
0 and 7-3 mol%, and 0.7 to 2.4 mol% relative to the composition in terms of Al to Al ₂ O _3, relative to the composition in terms of Si to SiO _2. A piezoelectric ceramic composition comprising 1 to 1.5 mol%. _{(Pb u A 1-u)} v {(Zn 1/3 Nb 2/3) x Ti y Zr z} 2-v O 3 (I) where, in the above composition formula (I), A is La, Nd, P
r and Bi are at least one element selected from the group consisting of r and Bi, and u and v are each 0.92 ≦ u ≦ 0.
99, 0.97 ≦ v ≦ 1.03, and x, y and z
Are respectively 0.06 ≦ x ≦ 0.18 and 0.43 ≦ y ≦
0.53, 0.29 ≦ z ≦ 0.51, and x +
The relationship of y + z = 1 is satisfied. 2. A composition represented by the following composition formula (II), wherein Al is converted to Al ₂ O ₃ , and the composition is added to the composition in an amount of 0.
A piezoelectric ceramic composition comprising ₇ to 2.4 mol% and 0.1 to 1.5 mol% of Si in terms of SiO ₂ with respect to the composition. _{t (Pb u A 1-u} ) v [(Zn 1/3 Nb 2/3) x Ti y Zr z] 2-v O 3 - (1-t) YMnO 3 (II) where the composition formula (II ), A is La, Nd, P
r and Bi are at least one element selected from the group consisting of
≤ 0.994, 0.92 ≤ u ≤ 0.99, 0.97 ≤ v
≦ 1.03, and x, y and z are each 0.06
≦ x ≦ 0.18, 0.43 ≦ y ≦ 0.53, 0.29 ≦
z ≦ 0.51 and the relationship x + y + z = 1 is satisfied. 3. A piezoelectric transformer comprising the piezoelectric ceramic composition according to claim 1. 4. The piezoelectric transformer according to claim 3, further comprising a piezoelectric body composed of a piezoelectric ceramic composition, wherein the piezoelectric body includes a lengthwise polarization part and a thickness direction polarization part. 5. The piezoelectric body includes a first longitudinally polarized portion and a second longitudinally polarized portion that are separated from each other, and the thickness directionally polarized portion includes the first longitudinally polarized portion and the second longitudinally polarized portion. The piezoelectric transformer according to claim 4, wherein the piezoelectric transformer exists between the second longitudinally polarized portion and the second longitudinally polarized portion. 6. The piezoelectric transformer according to claim 5, wherein the piezoelectric body excites a fundamental vibration mode.