JP2008007335A - Piezoelectric ceramic composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric ceramic composition which has higher dielectric constant εr, electromechanical coupling factor k, and vibration limit speed Vmax and is useful in order to make a piezoelectric transformer high in output. <P>SOLUTION: In the piezoelectric ceramic composition, the compositional formula of main components 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 a, b, c, y and z in the formula are defined as the range of 0.46≤y/(y+z)≤0.54 and 0.03<a+b+c≤0.10. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric ceramic composition used for various piezoelectric devices, and more particularly to a piezoelectric ceramic composition suitable for a piezoelectric transformer.

  In recent years, piezoelectric transformers using piezoelectric materials have been widely used in backlight inverters for liquid crystal displays because they have higher efficiency and higher step-up ratio and are suitable for lowering the height compared to electromagnetic transformers. Yes.

  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, The Institute of Electronics, Information and Communication Engineers, April 21, 1992, US92-3, p. 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 meet the demand for higher output of the inverter, in order to ensure the life of the piezoelectric transformer and the stable high output characteristics, the relative dielectric constant εr, the electromechanical coupling coefficient k, and the vibration limit. It is to provide a piezoelectric ceramic composition having a higher velocity 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 It is a piezoelectric ceramic composition in the range of ≦ y / (y + z) ≦ 0.54.

  The present invention is the above piezoelectric ceramic composition in which a part of Pb in the composition formula is replaced with Ca.

  This invention is the said piezoelectric ceramic composition reduced in the range of 1.0 mol% or less from the stoichiometric Pb content in the said composition formula.

The present invention is a piezoelectric ceramic composition having a vibration velocity limit Vmax of 0.3 m / s or more, a relative dielectric constant εr of 600 or more, and an electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode of 0.6 or more. . 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 a piezoelectric ceramic composition having a fracture vibration speed of 1.0 m / s or more. Here, the breaking vibration speed is a vibration speed that leads to the destruction of the piezoelectric vibrator that is resonantly driven at room temperature.

According to the present invention, a piezoelectric ceramic composition 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 is obtained. be able to.

  Further, by substituting a part of Pb with Ca and reducing the amount of Pb, the balance between crystal grain growth and sintering densification can be adjusted, so that the coercive electric field of the material can be lowered, and the piezoelectric element The amount of energy at the time of manufacture can be suppressed. Here, the coercive electric field is a high electric field for polarizing ferroelectric ceramics. Moreover, the electromechanical coupling coefficient can be increased by reducing the amount of Pb.

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

  Hereinafter, the piezoelectric ceramic composition of the present invention will be described in detail by 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-based piezoelectric ceramic Pb (Mn _1/3 Sb _2/3 ) in which a composite perovskite, which is a ceramic composition for a piezoelectric transformer, is dissolved as a third component. What added Pb (Mn _1/3 Nb _2/3 ) O ₃ and Pb (Sb _1/2 Nb _1/2 ) O ₃ as fourth and fifth main components to O ₃ —PbZrO ₃ —PbTiO ₃ in, it can be increased a, b, c, y, by selecting the composition range of z, the relative dielectric constant .epsilon.r, and an electromechanical coupling coefficient k _33.

In the present invention, a + b + c is set to be larger than 0.03 and equal to or smaller than 0.10 because when k is equal to or smaller than 0.03 or larger than 0.10, k ₃₃ cannot be 0.6 or larger.

Also, to that y / a (y + z) 0.46 or 0.54 or less, y / (y + z) is greater than 0.54, the a + b + c is less than 0.03, k ₃₃ is obtained at least 0.6 Because it is not possible.

  If a + b + c is greater than 0.03 and 0.10 or less, and y / (y + z) is 0.46 or more and 0.54 or less, the vibration speed limit Vmax is 0.3 or more. When a + b + c is less than 0.03, the vibration speed limit Vmax is smaller than that when 0.0+ or more.

  Regarding the substitution of the piezoelectric ceramic composition of the present invention from Pb to Ca, the coercive electric field can be lowered to 1.3 to 0.9 kV / mm when the substitution amount is increased to 0 to 7.5%. Further, the coercive electric field can be further lowered by increasing the composition ratio of y / (y + z).

However, a piezoelectric ceramic composition polarized at a coercive electric field of 0.6 kV / mm or less has a low k ₃₃ . Further, when the Ca substitution amount is increased, the fracture vibration speed tends to decrease.

  From these conditions, the preferable substitution amount of Pb to Ca that can achieve the effect of the present invention is 0 to 2.5%, and the coercive electric field at that time is 0.9 to 1.2 kV / mm.

  As the Pb content of the piezoelectric ceramic composition of the present invention is decreased from 0 to 1.0 mol%, the electromechanical coupling coefficient also increases. Furthermore, the electromechanical coupling coefficient also increases with the composition of y / (y + z), and the maximum value is obtained when Pb decreases by 1.0% and y / (y + z) = 0.50.

Next, 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 to prepare samples for evaluating 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.

For evaluation of the electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode, it was processed into a rectangular plate of 3 mm × 3 mm × 10 mm.

  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 is represented by an effective vibration speed Ve [formula (2)] 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, 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.

  The fracture vibration speed was measured by measuring the vibration speed of the piezoelectric transformer with a laser Doppler vibration velocimeter. The test was performed by increasing the driving voltage until the sample was damaged in the resonance driving state.

Table 1 shows the evaluation results of each sample composition of the piezoelectric ceramic composition of the present invention, and shows the dielectric constant εr, the vibration speed limit Vmax, and the electromechanical coupling coefficient k ₃₃ in the longitudinal vibration mode as the piezoelectric characteristic evaluation results. Yes. A sample with * in front of the sample number indicates that the sample is outside the scope of the present invention.

  The component composition of each sample will be described from Table 1. Sample numbers 1 to 3 are a + b + c = 0.020 and y / (y + z) = 0.480 to 0.500. Sample numbers 4 to 7 are a + b + c = 0.0870 and y / (y + z) = 0.480 to 0.510. Sample numbers 8 to 14 are a + b + c = 0.0726, y / (y + z) = 0.460 to 0.540. Sample numbers 15 to 21 are a + b + c = 0.580 and y / (y + z) = 0.480 to 0.530. Sample numbers 22 to 24 are a + b + c = 0.0435 and y / (y + z) = 0.510 to 0.530. Sample numbers 25-29 are a + b + c = 0.0290, y / (y + z) = 0.520-0.550.

Summarizing k ₃₃ of the evaluation results in Table 1, in sample numbers 25 to 29 with a + b + c = 0.0290, y / (y + z) = 0.520 to 0.550, but k ₃₃ is 0 in this composition range. Less than 6.

In sample numbers 22 to 24 where a + b + c = 0.0435, y / (y + z) = 0.510 to 0.530. However, in this composition range, k ₃₃ was 0.6 or more.

Among sample numbers 15 to 21 with a + b + c = 0.580, sample number 15 with y / (y + z) = 0.480 had k ₃₃ of 0.600. In the sample number 21 where y / (y + z) = 0.530, k ₃₃ was 0.600. For sample numbers 16-20 of y / (y + z) = 0.490-0.520, k ₃₃ is greater than 0.600, especially for sample number 18 of y / (y + z) = 0.505, k ₃₃ is A maximum value of 0.719 was obtained.

Among the sample No. 8-14 is a + b + c = 0.0726, y / (y + z) = Sample No. 8 of 0.460, k ₃₃ is next 0.602, y / (y + z ) = 0.540 samples At number 14, k ₃₃ became 0.600. In sample numbers 9 to 13 of y / (y + z) = 0.480 to 0.525, k ₃₃ was larger than 0.600.

In sample numbers 4 to 7 where a + b + c = 0.0870, y / (y + z) = 0.480 to 0.510, but in this composition range, k ₃₃ was 0.600 or more.

In the sample numbers 1 to 3 where a + b + c = 0.020, y / (y + z) = 0.480 to 0.500. In this composition range, k ₃₃ was less than 0.600.

FIG. 1 is a graph of the measured value of k ₃₃ for each composition of the piezoelectric ceramic composition of the present invention. The abscissa is y / (y + z) and the ordinate is k ₃₃ for the above evaluation results. k ₃₃ ≧ 0.600 except samples 1 to 3 where a + b + c = 0.020 and samples 25 to 29 where a + b + c = 0.0290.

From these results, k ₃₃ ≧ 0.600 was satisfied in the composition range 0.03 <a + b + c ≦ 0.10, 0.46 ≦ y / (y + z) ≦ 0.54 of the piezoelectric ceramic composition of the present invention.

  The relative dielectric constant εr was 600 or more in any sample from Table 1.

  As shown in Table 1, the vibration speed limit Vmax increased substantially in proportion to the value of a + b + c. Sample number 29 of a + b + c = 0.0290 and y (y + z) = 0.550 was the minimum value, which was 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.

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

  FIG. 2 is a graph of the coercive electric field value with respect to the Ca substitution amount from Pb of the piezoelectric ceramic composition of the present invention. The result of measuring the coercive electric field Ec at 160 ° C. by changing the substitution amount of Pb to Ca when y / (y + z) = 0.5 from 0 to 7.5%, and the substitution amount of Pb to Ca The results of measuring the coercive electric field Ec at 160 ° C. by changing y / (y + z) at 5.0% from 0.49 to 0.52 are shown.

  When y / (y + z) = 0.5, the Ca substitution amount is 0% and Ec = 1.32 kV / mm, whereas when the substitution amount is 7.5%, Ec = 0.89 kV / mm and the Ca substitution amount are Increasing the coercive electric field Ec decreased. When the Ca substitution amount is 5%, Ec = 1.13 kV / mm at y / (y + z) = 0.49, whereas Ec = 0.9 kV / mm at y / (y + z) = 0.52. .

  Therefore, the substitution of Pb to Ca reduces the coercive electric field Ec, so that the voltage required for the polarization process can be lowered and the amount of energy at the time of manufacturing the piezoelectric element can be suppressed.

FIG. 3 is a graph of the Pb to Ca substitution amount and k ₃₃ of the piezoelectric ceramic composition of the present invention, as well as the measured values of the fracture vibration rate. The substitution amount from Pb to Ca is 0 to 4.5%. These are the measured value of k ₃₃ of the vibrator polarized at 0.4 kV / mm to 1.2 kV / mm and the measured value of the breaking vibration speed.

When the Ca substitution amount was 0%, k ₃₃ was 0.51 even when the polarization electric field was 1.17 kV / mm. However, when the Ca substitution amount was 4.5%, the polarization electric field was 0.98 kV / mm and k ₃₃ was When the Ca substitution amount was increased to 0.55, the polarization electric field could be lowered. However, the sample polarized at a polarization electric field of 0.6 kV / mm or less had k ₃₃ of 0.4 or less.

On the other hand, paying attention to the destruction vibration speed, when the Ca substitution amount 0% irrespective of the polarization electric field, but constant at approximately 3m / s, Ca substitution amount of 4.5% at k ₃₃ is in polarization field 0.98kV / mm A tendency to decrease to 2 m / s was observed.

  From FIG. 3, the fracture vibration rate was constant in the case of a piezoelectric ceramic composition polarized with Pb to Ca substitution of 2.5% and a polarization electric field of 0.8 kV / mm or more.

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

  From 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 was reduced by 1.0%, kr reached a maximum of 0.686. 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 coercive electric field value with respect to Ca substitution amount from Pb of the piezoelectric ceramic composition of this invention. Graph of Ca substitution amount of Pb of the piezoelectric ceramic composition and k _33, and the measured value of breaking vibration speed 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)

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 ≦ y / (y + z) A piezoelectric ceramic composition characterized by being in the range of ≦ 0.54.   The piezoelectric ceramic composition according to claim 1, wherein a part of Pb in the composition formula is replaced with Ca.   3. The piezoelectric ceramic composition according to claim 1, wherein the piezoelectric ceramic composition is reduced in a range of 1.0 mol% or less from the stoichiometric Pb content in the composition formula. The vibration speed limit Vmax is 0.3 m / s or more, the relative dielectric constant εr 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.   The piezoelectric ceramic composition according to any one of claims 1 to 4, wherein a fracture vibration speed is 1.0 m / s or more.

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