JP2003026477A - Porcelain material for piezoelectric transformer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a porcelain material for a piezoelectric transformer which can be driven even at a high vibrating speed of >=2 times the vibrating speed of the conventional material or large amplitude and has a high specific dielectric constant and electro-mechanical coupling coefficient. SOLUTION: The porcelain material for the piezoelectric transformer is >=0.45 m/s in Vmax, if the vibrating speed when the rising temperature at the vibration node of a piezoelectric vibrator attains 20 deg.C in the state that the piezoelectric vibrator is kept resonantly driven at ordinary temperature is defined as a vibrating speed threshold Vmax in addition, the material described above is >=500 in specific dielectric constant εr and is >=0.50 in the electromechanical coupling coefficient K33 in a longitudinal vibration mode. The porcelain material for the piezoelectric transformer is expressed by a composition formula aPbZrO3 -bPbTiO3 -cPb(Mn1/3 Sb2/3 )O3 (where a+b+c=1) and the composition range thereof exists within a region (not inclusive of the ranges on lines) enclosed by the lines connecting the composition points W(a=0.59, b=0.40, c=0.01), X(a=0.40, b=0.59, c=0.01), Y(a=0.33, b=0.59, c=0.01) and Z(a=0.52, b=0.40, c=0.08).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a piezoelectric ceramic material used for a piezoelectric transformer.

[0002]

2. Description of the Related Art In recent years, piezoelectric transformers using piezoelectric materials have been widely used in inverters for liquid crystal display backlights because they have higher efficiency and booster ratio than electromagnetic transformers and are suitable for low profile. It is used. With the increase in the size of liquid crystal displays and the size reduction of inverters, further increase in mechanical output is required for piezoelectric materials used in piezoelectric transformers.

Further, it is required to suppress energy loss when converting the electric energy of the piezoelectric material into mechanical vibration energy. As the operating vibration amplitude or vibration speed increases, heat is generated due to internal energy loss, so the vibration amplitude that can be excited eventually reaches the limit value,
That is, the vibration velocity limit value is reached, and further dielectric breakdown of the material is caused. Now, assuming that the vibration speed is the maximum vibration amplitude ξm of the vibrator and the effective vibration speed V that can be calculated from the measurement of the resonance frequency fr of the vibrator,
V is represented by the following formula 1. (Reference: Seiji Hirose, IEICE Technical Report, US92-3 Automatic measurement of high power characteristics of piezoelectric vibrators, see)

[Equation 1] In this way, when the vibration level is expressed by the vibration speed, the limit of the vibration speed (20 ° C
Vibration speed when generating heat, Vmax) is 0.2 m / s
It stayed around.

In the case of a piezoelectric transformer, its output value P
Out has a relation of the following formula 2 with the relative dielectric constant εr, which is a material characteristic value, the electromechanical coupling coefficient K, and the vibration velocity V.

[0005]

[Equation 2] From the equation (2), in order to obtain a high output, it is important in the material properties that the usable vibration velocity level is high, but it is also necessary that the values of εr and K are large. Therefore, it can be said that it is difficult to achieve a high output with a material having a low εr and a low K even if only Vmax is high.

[0006]

As described above, since the conventional piezoelectric ceramic material is driven at a low vibration speed with an upper limit of about 0.2 m / s, the output characteristics of the piezoelectric transformer are further improved. Was difficult.

Therefore, the technical problem of the present invention is that a porcelain material for a piezoelectric transformer that can be driven at a high vibration speed or a large amplitude which is more than twice that of conventional materials, and has a high relative dielectric constant and electromechanical coupling coefficient. To provide.

[0008]

SUMMARY OF THE INVENTION The present invention is intended to be a high vibration velocity was found composition range drivable piezoelectric ceramic material, the composition formula aPbZrO ₃ -bPbTiO ₃ -cPb
(Mn _1/3 Sb _2/3 ) O ₃ (where a + b + c =
1) and its composition range is represented by the following composition points shown in the three-component composition diagram of FIG. 1: W (a = 0.59, b = 0.4).
0, c = 0.01); X (a = 0.40, b = 0.5)
9, c = 0.01); Y (a = 0.33, b = 0.5)
9, c = 0.08); Z (a = 0.52, b = 0.4)
0, c = 0.08) within a region surrounded by a line (not including the line), and the average grain size of the sintered body is 5 μm.
It has been found that by the following, a porcelain material for a piezoelectric transformer that can be stably driven without mechanical destruction can be obtained.

That is, by controlling the composition range and the average particle size range of the sintered body according to the present invention, the vibration velocity limit V, which has been difficult to achieve in the past, can be obtained.
Vmax ≧ 0.45m / where max is more than twice that of conventional products
A piezoelectric ceramic material having a relative permittivity εr of 500 or more and an electromechanical coupling coefficient K ₃₃ in the longitudinal vibration mode of 0.50 or more can be obtained.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a three-component composition diagram of the piezoelectric ceramic material of the present invention. The piezoelectric ceramic material of the present invention comprises a sintered body,
Used in piezoelectric transformers, W, X, Y, and Z in the drawings represent composition points, and the composition range of the present invention is from the composition of the composition region not included in the range indicated by diagonal lines in the drawing and the boundary line thereof. Become.

That is, in the porcelain material for piezoelectric transformer of the present invention, the composition formula aPbZrO ₃ -bPbTiO ₃ -cPb is used.
(Mn _1/3 Sb _2/3 ) O ₃ (where a + b + c =
1) and its composition range is represented by the following composition points shown in the three-component composition diagram of FIG. 1: W (a = 0.59, b = 0.4).
0, c = 0.01); X (a = 0.40, b = 0.5)
9, c = 0.01); Y (a = 0.33, b = 0.5)
9, c = 0.08); Z (a = 0.52, b = 0.4)
0, c = 0.08), which is within a region surrounded by a line connecting the lines (not including the line).

Specific examples of the present invention will be described below.

(Example) As a starting material for obtaining the material of the present invention
PbO, ZrO_Two, TiO_Two, MnCO _Three, Sb_Two
O_ThreeEach powder of was used.

A predetermined amount of each raw material powder was weighed, wet mixed with a ball mill, and the mixed powder was calcined in the atmosphere for 2 hours. The calcined powder was crushed, mixed with a binder, molded, further debindered, and baked in the atmosphere for 2 hours. After cutting the sintered body and processing it into a rectangular plate of 43 × 7 × 1 mm, silver electrodes were baked on both main surfaces facing each other, and a DC electric field of 4 kV / mm in silicon oil was applied at 100 ° C. for 15 minutes. It was polarized.

After the polarization treatment, it was left at room temperature for 24 hours to excite the fundamental mode of piezoelectric transverse effect longitudinal vibration, and the vibration velocity limit was measured.

The vibration velocity is represented by the following formula 3 effective vibration velocity V which can be calculated from the measurement of the maximum tip vibration amplitude ξm of the vibrator and the resonance frequency fr of the vibrator, as described in the prior art.

[0018]

[Equation 3] The vibration velocity limit is the temperature rise (difference between the room temperature and the temperature of the vibrator) ΔT that is excited by the internal energy loss of the vibrator by measuring the temperature at the vibration node of the piezoelectric vibrator.
The vibration speed at 0 ° C. was expressed as Vmax, and this was defined as the vibration speed limit.

The measurement results are shown in Table 1 below. here,
Samples marked with "*" are comparative samples that are outside the scope of the present invention.

Next, the reason for limiting the compounding ratio (composition ratio) of each compound will be described below.

First, Pb (Mn _1/3 Sb _2/3 ) O ₃
When the amount c is 1 mol% or less, the loss due to internal friction accompanying the movement of the ferroelectric domain wall is large, so the vibration velocity limit is low, and the relative permittivity and electromechanical coupling coefficient are low. Also,
When the amount of c is 8 mol% or more, the relative dielectric constant and the electromechanical coupling coefficient decrease, which is not preferable.

If the compounding ratio of the PbZrO ₃ amount a is set to a ratio not within the claims, the relative permittivity and the electromechanical coupling coefficient are also extremely lowered, which is not suitable. PbTiO ₃ amount b is a,
If c is decided, it will be decided inevitably.

Therefore, a relative permittivity of 500 or more and 0.50
The above-mentioned longitudinal vibration mode electromechanical coupling coefficient and the vibration velocity limit of 0.45 m / s or more are limited within the composition range of the present invention. Further, here, let us try to calculate a parameter that is an output coefficient that can determine the magnitude of the output value of the piezoelectric transformer. The output coefficient Pc is a value defined by the following Expression 4.

[0024]

[Equation 4] Table 1 below shows the calculation results by the above-mentioned equation (4). From this, it is expected that Pc will be 45 or more in the composition of the present invention, and a higher output piezoelectric transformer can be realized. on the other hand,
Outside the scope of this claim, since Pc <45, even if Vm
Even if ax is high, a high output transformer cannot be realized.

[0025]

[Table 1] In addition, as shown in FIG. 2, it was confirmed that Vmax tends to decrease as the average particle size of the sintered body increases, and further, 5 μm.
Exceeding m may cause mechanical breakdown during driving, and is therefore excluded from the scope of the present invention.

[0026]

As described above, the material according to the present invention has high vibration velocity, relative permittivity and electromechanical coupling coefficient,
Therefore, the output characteristics of the piezoelectric transformer can be improved, and the industrial value is great.

[Brief description of drawings]

FIG. 1 is a three-component composition diagram showing a composition range (claim 2) of a porcelain composition for a piezoelectric transformer of the present invention.

2 is an example No. of the present invention. For the composition of 24, V
It is a figure showing the relationship between max and a particle size.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Katsuno Choshi             6-7-1, Koriyama, Taihaku-ku, Sendai City, Miyagi Prefecture             Tokin Co., Ltd. (72) Inventor Yoichi Mamiya             6-7-1, Koriyama, Taihaku-ku, Sendai City, Miyagi Prefecture             Tokin Co., Ltd. (72) Inventor Toshiyuki Tachikawa             231 Sugazawa, Yamazaki-cho, Shiawasu-gun, Hyogo Prefecture             Kinceramics Co., Ltd. F term (reference) 4G031 AA11 AA12 AA19 AA32 AA34                       BA10 CA04

Claims (3)

[Claims] 1. The temperature rise at the vibration node of the piezoelectric vibrator is 2 when the piezoelectric vibrator is resonantly driven at room temperature.
When the vibration velocity when reaching 0 ° C. is defined as the vibration velocity limit Vmax, Vmax is 0.45 m / s or more, the relative dielectric constant εr is 500 or more, and the electromechanical coupling coefficient K ₃₃ in the longitudinal vibration mode is 0.50. The above is a porcelain material for piezoelectric transformers. 2. The porcelain material for piezoelectric transformer according to claim 1, wherein the composition formula is aPbZrO ₃ -bPbTiO ₃ -c.
Pb (Mn _1/3 Sb _2/3 ) O ₃ (however, a + b +
c = 1), and the composition range is the following composition point shown in the three-component composition diagram of FIG. 1; W (a = 0.59, b = 0.40, c = 0.01) X ( a = 0.40, b = 0.59, c = 0.01) Y (a = 0.33, b = 0.59, c = 0.08) Z (a = 0.52, b = 0. 40, c = 0.08) within a region (not included on the line) surrounded by a line connecting the two. 3. The porcelain material for a piezoelectric transformer according to claim 2, which is substantially composed of a sintered body having an average particle diameter of 5 μm or less.