JP2008280204A - Piezoelectric ceramic composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition having large relative permittivity (εr) and an electromechanical coupling coefficient (k) and vibration limit speed Vmax to attain high output of a piezoelectric transformer. <P>SOLUTION: In the composition of a main component which is expressed by aPb(Mn<SB>1/3</SB>Sb<SB>2/3</SB>)O<SB>3</SB>-bPb(Mn<SB>1/3</SB>Nb<SB>2/3</SB>)O<SB>3</SB>-cPb(Sb<SB>1/2</SB>Nb<SB>1/2</SB>)O<SB>3</SB>-yPbZrO<SB>3</SB>-zPbTiO<SB>3</SB>(where, a+b+c+y+z=1) and in which the a, b, c, x, y and z is in a range of 0.46≤y/(y+z)≤0.54 and 0.03<a+b+c≤0.10, Fe is added in a range of 0<Fe≤0.5 wt.%. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a piezoelectric ceramic composition mainly composed of lead zirconate titanate used for various piezoelectric devices, and more particularly to a piezoelectric ceramic composition suitable as a high-power piezoelectric transformer element material.

  In recent years, a piezoelectric transformer using a piezoelectric ceramic composition has been used for an inverter for a backlight of a liquid crystal display because it has a higher efficiency and a step-up ratio than those of an electromagnetic transformer and is suitable for a low profile.

  With the increase in the size of liquid crystal displays and the size of inverters, the piezoelectric material used for piezoelectric transformers is required to further increase its mechanical output. Further, it is required to suppress energy loss when converting the electrical 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 speed limit value, and further causes dielectric breakdown of the material. It is.

  Now, assuming that the vibration speed is a vibration speed V that can be calculated from the measurement of the maximum tip vibration amplitude ξm of the vibrator and the resonance frequency fr of the vibrator, V is expressed by Expression (1). As described in Non-Patent Document 1.

  V = 2 × π × fr × ξm (1)

  The effective vibration speed Ve is expressed by Expression (2).

Ve = 2 ^1/2 × π × fr × ξm (2)

  Next, the vibration speed limit value will be described. The piezoelectric inverter is required to be able to be driven in a 40 ° C. environment, which is the upper limit of the operating environment temperature of a device such as a personal computer. This is to prevent the piezoelectric inverter from stopping due to a rise in the temperature of each component as the environmental temperature rises and thermal runaway. Regarding the piezoelectric transformer, it has been confirmed that if the temperature rise of a single unit during driving is 20 ° C., the use environment conditions of the apparatus can be satisfied. When the vibration speed when the rising temperature at the vibration node of a piezoelectric vibrator that is resonantly driven at room temperature reaches 20 ° C. is defined as the vibration speed limit Vmax, the vibration speed limit Vmax is 0 in the conventional piezoelectric ceramic composition. It was 3 m / s.

Furthermore, Patent Document 1 discloses an example of a piezoelectric ceramic composition that can be driven at a high vibration speed. Here, defining an average particle size range of composition formula _{aPbZrO 3 -bPbTiO 3 -cPb (Mn 1/3} Sb 2/3) O 3 ( where, a + b + c = 1 ) specific composition range represented by the sintered body As a result, the vibration limit speed Vmax ≧ 0.45 m / s was realized.

  Further, the output value Pout of the piezoelectric transformer has a relation of the relative dielectric constant εr, the electromechanical coupling coefficient k, and the vibration speed V, which are material characteristic values, as shown in Expression (3).

Pout∝εr × k ² × V ² (3)

  In order to obtain a higher output than Expression (3), it is important that the usable vibration speed level is high in the material characteristics, but it is also necessary that the values of εr and k be large.

  In a device used at a high vibration speed level, such as a piezoelectric transformer, the mechanical strength of ceramics is required to be high. Even if a material satisfying high characteristics (εr, k, Vmax) is obtained, if the mechanical strength is low, it cannot be used stably at a high vibration speed level, and the reliability as a product is also lowered. Because it does.

JP 2003-26477 A Seiji Hirose, “Automatic Measurement of High Power Characteristics of Piezoelectric Vibrators”, IEICE Technical Report, IEICE, April 21, 1992, US92-3, P.A. 17-22

  However, in the technique described in Patent Document 1, if an operation is performed at a high vibration speed in order to obtain a high-output piezoelectric transformer, there is a risk that the piezoelectric transformer itself may break down due to the distortion generated, which is stable. There was a problem that the piezoelectric transformer characteristics could not be secured.

  Accordingly, an object of the present invention is to provide a high relative dielectric constant εr, electromechanical coupling coefficient k, vibration, in order to ensure a long life and stable high output characteristics of a piezoelectric transformer in response to a demand for high output of an inverter. It is to provide a piezoelectric ceramic composition having a critical speed Vmax.

That is, according to the present invention, the composition formula of the main component is aPb (Mn _1/3 Sb _2/3 ) O ₃ -bPb (Mn _1/3 Nb _2/3 ) O ₃ -cPb (Sb _1/2 Nb _{1 / 2} ) O ₃ —yPbZrO ₃ —zPbTiO ₃ (where a + b + c + y + z = 1), and a, b, c, y, z in the composition formula are 0.03 <a + b + c ≦ 0.10, 0.46 ≦ The piezoelectric ceramic composition is characterized in that y / (y + z) ≦ 0.54.

  The present invention is the above-described piezoelectric ceramic composition, wherein Fe is added in a range of 0 <Fe ≦ 0.5 wt%.

  The present invention is the above-described piezoelectric ceramic composition, wherein the Pb content is reduced in a range of 0 <Pb ≦ 1.0 mol%.

The present invention is characterized in that the vibration velocity limit Vmax is 0.3 m / s or more, the relative dielectric constant is 600 or more, and the electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode is 0.6 or more. The piezoelectric ceramic composition. Here, the vibration speed limit is a vibration speed at which the rising temperature at the vibration node of the piezoelectric vibrator that is resonantly driven at room temperature reaches 20 ° C.

  The present invention is the above-described piezoelectric ceramic composition, wherein the temperature change rate of the relative permittivity is 35% or less. Here, the temperature change rate of the relative permittivity is based on the relative permittivity of the piezoelectric ceramic composition at 20 ° C., and the temperature is increased by 80 ° C., that is, the relative permittivity at 100 ° C. is obtained. The temperature change rate is obtained.

As described above, according to the present invention, a piezoelectric material having an electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode of 0.6 or more, a relative dielectric constant εr of 600 or more, and a vibration limit speed Vmax of 0.3 m / s or more. A porcelain composition can be obtained.

  Also, by adding other elements and reducing the amount of Pb, the balance between crystal grain growth and sintering densification can be adjusted, so the temperature change rate of the relative dielectric constant of the material should be reduced to 35% or less. Therefore, the rate of change in material characteristics with respect to the temperature change in the usage environment is reduced, and a stable piezoelectric transformer can be obtained.

  Therefore, according to the present invention, a piezoelectric ceramic composition for a piezoelectric transformer capable of high output can be provided.

  Hereinafter, a piezoelectric ceramic composition according to the present invention will be described in detail based on embodiments.

The piezoelectric ceramic composition according to the invention _{aPb (Mn 1/3 Sb 2/3) O} 3 -bPb (Mn 1/3 Nb 2/3) O 3 -cPb (Sb 1/2 Nb 1/2) O 3 -yPbZrO _3- zPbTiO ₃ (where a + b + c + y + z = 1) is a multi-component PZT piezoelectric ceramic Pb (Mn _1/3 Sb _2/3 ) O in which a composite perovskite, which is a ceramic composition for a piezoelectric transformer, is dissolved as a third component. _3- PbZrO ₃ -PbTiO ₃ to which Pb (Mn _1/3 Nb _2/3 ) O ₃ and Pb (Sb _1/2 Nb _1/2 ) O ₃ are added as the fourth and fifth main components. It can increase a, b, c, y, by selecting the composition range of z, the relative dielectric constant .epsilon.r, and an electromechanical coupling coefficient k _33.

Optimum composition range of the present invention, a + b + c is at greater than 0.03 to 0.10, y / (y + z) is 0.46 or more 0.54 or less, .epsilon.r 600 or more, k ₃₃ 0.6 The above is obtained.

If a + b + c is less than 0.03, k ₃₃ is not obtained at least 0.6.

When a + b + c is larger than 0.10, k ₃₃ cannot be 0.6 or more.

If y / (y + z) is greater than 0.54 and a + b + c is less than 0.03, k ₃₃ cannot be 0.6 or more.

  If a + b + c is larger than 0.03 and not larger than 0.10 and y / (y + z) is not smaller than 0.46 and not larger than 0.54, the vibration speed limit Vmax is not smaller than 0.3.

  When a + b + c is less than 0.03, the vibration speed limit Vmax is smaller than that when 0.0+ or more.

  The temperature change rate of the relative permittivity in the piezoelectric ceramic composition of the present invention is 37% or more without adding Fe, but when Fe is added in the range of 0 to 0.6 wt% or less, the temperature of the relative permittivity is increased. The rate of change can be reduced to 35% or less.

Here, in the piezoelectric ceramic composition of the present invention, the electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode with respect to the added amount of Fe is within a range of Fe from 0 to 0.5 wt% and y / (y + z) is 0. If it is .46 or more and 0.54 or less, it will be 0.6 or more.

  However, in the piezoelectric ceramic composition of the present invention, when the addition amount of Fe is 0.6 wt%, y / (y + z) is 0.46 to 0.47, 0.52 to 0.54 or less, and 0.6. The above cannot be obtained.

  From these conditions, the desirable addition amount of Fe for obtaining the effects of the present invention is greater than 0 and 0.5 wt% or less.

  Further, in the piezoelectric ceramic composition of the present invention, with respect to the Pb weight loss, the sintering density is 1100 ° C., which is the same as the sintering density even if the Pb content is reduced from 0 to 1 mol%. is there.

  When the amount of Pb was reduced from 0 to 1 mol% and the piezoelectric ceramic composition having the same sintering density at a sintering holding temperature of 1100 ° C. was measured, the vibrational electromechanical coupling coefficient kr in the radial direction was measured. When the amount is decreased from 0 to 1 mol%, Kr is improved and a high electromechanical coupling coefficient is obtained.

Examples of the present invention will be described in detail. As starting materials for obtaining a piezoelectric ceramic composition, lead oxide (PbO), titanium oxide (TiO ₂ ), zirconium oxide (ZrO ₂ ), manganese carbonate (MnCO ₃ ), antimony oxide (Sb ₂ O ₃ ), niobium oxide (Nb) ₂ O ₅ ) and calcium carbonate (CaCO ₃ ) powders were used.

  A predetermined amount of each raw material powder was weighed and wet-mixed with a ball mill, the mixed powder was dehydrated, dried and then pre-fired in an alumina mortar, and each pre-fired powder was wet-ground with a ball mill.

  Next, a binder is mixed with the pre-fired pulverized powder obtained by dehydration and drying, and pressed to form a shape of φ20 × thickness 3 mm. This molded body was fired at a temperature of 900 to 1260 ° C. for 2 to 6 hours.

  Each sintered body was cut into a thickness of 1 mm. Next, silver paste was applied to both surfaces, baked at 450 ° C., and electrodes were formed, thereby preparing samples for evaluation of piezoelectric magnetic compositions having different compositions.

  For evaluation of the vibration speed limit Vmax, a rectangular plate having a length of 12 mm, a width of 3 mm, and a thickness of 1 mm was processed.

The evaluation of the electromechanical coupling coefficient k _33, was processed into a rectangular plate of 3mm × 3mm × 10mm.

  For evaluation of the fracture vibration speed, a Rosen-type piezoelectric transformer having a shape of 40 × 4 × 1.5 mm was processed.

  Each sample was subjected to polarization treatment and allowed to stand at room temperature for 24 hours to evaluate the characteristics.

  The vibration speed was calculated from the equation (2) as the effective vibration speed V as described in the prior art.

Ve = 2 ^1/2 × π × fr × ξm (2)

  The vibration speed limit is a vibration speed at which the temperature rise (difference between room temperature and the temperature of the vibrator) ΔT is 20 ° C., which is excited by the internal energy loss of the vibrator by measuring the temperature at the vibration node of the piezoelectric vibrator. This was expressed as Vmax, which was defined as the vibration speed limit.

In Table 1, the evaluation result of each sample composition of the piezoelectric ceramic composition of the present invention is shown. Composition _{formula, aPb (Mn 1/3 Sb 2/3)} O 3 -bPb (Mn 1/3 Nb 2/3) O 3 -cPb (Sb 1/2 Nb 1/2) O 3 -yPbZrO 3 -zPbTiO _{3 For the} piezoelectric ceramic composition represented by (where a + b + c + y + z = 1), samples were prepared with 29 types of compositions, and as a result of piezoelectric property evaluation, relative permittivity εr, vibration speed limit Vmax, electromechanical coupling in longitudinal vibration mode A coefficient k ₃₃ and a radial electromechanical coupling coefficient kr are shown. Samples with * in front of the sample number are samples outside the scope of the present invention.

  In Table 1, sample numbers 1 to 3 are samples outside the scope of the present invention, and a + b + c is larger than 0.1 and 0.1020. Sample numbers 4 to 7 are samples within the scope of the present invention, and a + b + c = 0.0870 and y / (y + z) = 0.480 to 0.510. Sample numbers 8 to 14 are samples within the scope of the present invention, and a + b + c = 0.0726 and y / (y + z) = 0.460 to 0.540. Sample numbers 15 to 21 are samples within the scope of the present invention, and a + b + c = 0.580 and y / (y + z) = 0.480 to 0.530. Sample numbers 22 to 24 are samples within the scope of the present invention, and a + b + c = 0.0435 and y / (y + z) = 0.510 to 0.530. Sample numbers 25 to 29 are samples outside the scope of the present invention, and a + b + c is smaller than 0.03 and 0.0290. For sample number 29, y / (y + z) is also larger than 0.54 and 0.550 outside the scope of the present invention.

In Table 1, in sample numbers 1 to 3, which are samples outside the scope of the present invention, k ₃₃ is less than 0.600.

Sample No. 4-7 as a sample in claims of the present invention, k ₃₃ was obtained more than 0.600.

Among sample numbers 8 to 14, which are samples within the scope of the present invention, in sample number 8 where y / (y + z) = 0.460, k ₃₃ = 0.602 and y / (y + z) = 0 For sample number 14 which is .540, k ₃₃ = 0.600. Then, the y / (y + z) = 0.480~0.525 sample No. is 9 to 13, k ₃₃ was greater than 0.600.

Among sample numbers 15 to 21, which are samples within the scope of the present invention, sample number 15 where y / (y + z) = 0.480 and sample number 21 where y / (y + z) = 0.530 are K ₃₃ = 0.600. Then, in sample numbers 16 to 20 where y / (y + z) = 0.490 to 0.520, k ₃₃ is greater than 0.600, and in sample number 18 where y / (y + z) = 0.505. , k ₃₃ is 0.719 becomes the maximum value is obtained.

In No. 22 to 24 are samples in claims of the present invention, k ₃₃ is obtained at least 0.6.

In sample numbers 25 to 29, which are samples outside the scope of the present invention, k ₃₃ is less than 0.6.

FIG. 1 is a graph of measured values of k ₃₃ for each composition of the piezoelectric ceramic composition of the present invention, where the horizontal axis is y / (y + z) and the vertical axis is k ₃₃ . Samples other than the sample numbers 1 to 3 which are a sample outside the scope of the present invention and have a + b + c = 0.102 and samples Nos. 25 to 29 which have a + b + c = 0.029 have k ₃₃ of 0.600 or more. .

From these results, 0.033 <a + b + c ≦ 0.10, 0.46 ≦ y / (y + z) ≦ 0.54, which is within the scope of the present invention, and k ₃₃ satisfied 0.600 or more. .

  In Table 1, the relative dielectric constant εr was 600 or more for any sample.

  Further, in Table 1, regarding the vibration speed limit Vmax, the sample number 29 which is a sample outside the claimed range of the present invention has a minimum value of 0.280 m / s. Sample number 7 with a + b + c = 0.0870 and y (y + z) = 0.510 was the maximum value, and Vmax was 0.740 m / s. In the composition range of the piezoelectric ceramic composition of the present invention 0.03 <a + b + c ≦ 0.10 and 0.46 ≦ y / (y + z) ≦ 0.54, Vmax was 0.47 m / s or more.

From the above, the composition range of the piezoelectric ceramic composition of the present invention is such that εr ≧ 600, k ₃₃ ≧ 0.600 when 0.03 <a + b + c ≦ 0.10 and 0.46 ≦ y / (y + z) ≦ 0.54. Vmax ≧ 0.30 m / s or more is optimal.

2 and 3 show the samples shown in Table 1, in which a + b + c = 0.0726, which is within the composition range of the piezoelectric ceramic composition of the present invention, and y / (y + z) is 0.46 to 0.54. It is the result of evaluating the temperature change rate of the relative permittivity when Fe is added to the numbers 8 to 14 and the electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode.

  FIG. 2 is a graph of the temperature change rate of the relative permittivity of the piezoelectric ceramic composition of the present invention, and is a result of obtaining the temperature change rate of the relative permittivity by adding Fe to each sample. The horizontal axis is y / (y + z), and the vertical axis is the temperature change rate of the dielectric constant.

  Here, the temperature change rate of the relative permittivity is obtained by calculating the relative permittivity of each sample at 20 ° C., increasing the temperature at 80 ° C., determining the relative permittivity at 100 ° C., and calculating the relative permittivity at 20 ° C. As a reference, the temperature change rate of the relative permittivity is obtained. In FIG. 2, the temperature change rate of the dielectric constant is obtained every time 0.1, 0.5, and 0.6 wt.% Fe is added, and the Fe addition amounts are 0.1 wt.%, 0.5 wt.%, And 0.6 wt. Indicated.

  The temperature change rate of the relative dielectric constant of the sample to which Fe was not added was the lowest at 37.4% in the sample number 10 where y / (y + z) = 0.49. In any sample, the temperature change rate of the relative dielectric constant decreased by 5% or more by adding 0.1 wt% Fe. When the amount of Fe added was 0.5 wt%, it decreased by about 1%, and there was not much change at 0.6 wt%. The minimum value of the temperature change rate of the relative permittivity was 30% when 0.5 wt% of Fe was added to y / (y + z) = 0.49 of sample number 10.

Figure 3 is a graph of the electromechanical coupling factor k ₃₃ in longitudinal vibration mode with respect to Fe amount of the piezoelectric ceramic composition of the present invention, the electromechanical coupling factor k ₃₃ in longitudinal vibration mode with the addition of Fe in each sample It is the result of measurement. The horizontal axis y / (y + z), the vertical axis represents the k _33. Seeking k ₃₃ and Fe each time adding 0.1,0.5,0.6wt%, were respectively added amount 0.1wt%, 0.5wt%, with 0.6 wt%.

The electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode is equivalent when the Fe addition amount is in the range of 0 to 0.5 wt%, and sample number 8 where y / (y + z) is 0.46 and y / (y + z) is 0. When the sample number was .54, the lowest value was 0.60.

However, when the added amount of Fe is 0.6 wt%, k ₃₃ decreases in any sample and y / (y + z) is 0 as compared to when the Fe added amount is in the range of 0 to 0.5 wt%. In sample numbers 8, 13, and 14 of .46, 0.525, and 0.54, k ₃₃ was 0.6 or less.

Therefore, from FIGS. 2 and 3, in samples Nos. 8 to 14 where y / (y + z) is 0.46 to 0.54, Fe is added in an amount of 0.1 to 0.5 wt%, and the electric current in the longitudinal vibration mode is The mechanical coupling coefficient k ₃₃ was 0.6 or more. Moreover, the temperature change rate of the dielectric constant was 35% or less.

FIG. 4 is a graph of measured values of Pb weight loss and sintered density of the piezoelectric ceramic composition of the present invention, a sample in which the Pb amount is not reduced (Pb weight loss 0 mol%), a sample in which 0.5 mol% and 1 mol% are reduced ( This is a result of measuring the sintered density by changing the sintering holding temperature with respect to (Pb loss 0.5 mol%, Pb loss 1 mol%). At a sintering holding temperature of 1100 ° C., the Pb loss 0 mol% was 7.86 g / cm ³ , and the Pb reduction 1 mol% was equivalent to 7.91 g / cm ³ .

  Therefore, according to the piezoelectric ceramic composition according to the present invention, a sufficient sintered density can be secured as the piezoelectric ceramic composition even if the Pb content is reduced within a range of 1 mol% or less.

  FIG. 5 is a graph of kr against the composition of the piezoelectric ceramic composition of the present invention and Pb loss, and the piezoelectric ceramic at Pb reduction of 0, 0.5, 1.0 mol% at the sintering holding temperature of 1100 ° C. shown in FIG. It is the result of measuring kr by changing y / (y + z) of the composition formula from 0.48 to 0.51 for a sample of the composition. Here, kr is a radial electromechanical coupling coefficient measured using a disk-shaped sample having a diameter of 17 mm and a thickness of 1 mm.

  In FIG. 5, when Pb was reduced in the range of 0 to 1.0%, kr increased. In particular, when y / (y + z) = 0.5 and Pb reduction was 1.0%, kr reached a maximum of 0.685. Therefore, the electromechanical coupling coefficient increased when Pb was reduced in the range of 0 to 1.0%.

Graph of the measured values of k ₃₃ for each composition of the piezoelectric ceramic composition of the present invention. The graph of the temperature change rate of the dielectric constant with respect to the addition amount of Fe of the piezoelectric ceramic composition of the present invention. Graph of k ₃₃ for the Fe amount of the piezoelectric ceramic composition of the present invention. The graph of the measured value of Pb weight loss and sintering density of the piezoelectric ceramic composition of the present invention. The graph of kr with respect to the composition and Pb weight loss of the piezoelectric ceramic composition of the present invention.

Claims (5)

The composition formula of the main component is
_{aPb (Mn 1/3 Sb 2/3) O} 3 -bPb (Mn 1/3 Nb 2/3) O 3 -cPb (Sb 1/2 Nb 1/2) O 3 -yPbZrO 3 -zPbTiO 3 ( provided that a + b + c + y + z = 1),
Piezoelectric ceramic composition characterized in that a, b, c, y and z in the composition formula are in a range of 0.03 <a + b + c ≦ 0.10 and 0.46 ≦ y / (y + z) ≦ 0.54. object.   The piezoelectric ceramic composition according to claim 1, wherein Fe is added in a range of 0 <Fe ≦ 0.5 wt%.   3. The piezoelectric ceramic composition according to claim 1, wherein the Pb content is reduced in a range of 0 <Pb ≦ 1.0 mol%. The vibration velocity limit Vmax is 0.3 m / s or more, the relative dielectric constant is 600 or more, and the electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode is 0.6 or more. The piezoelectric ceramic composition according to any one of the above.   5. The piezoelectric ceramic composition as described in any one of 1 to 4, wherein the temperature change rate of the dielectric constant is 35% or less.

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