JP2007284278A - Piezoelectric element material and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric element material which has strength nearly equal to that of a conventional one while having improved piezoelectric characteristics including quantity of distortion, to which various components and elements and wide compositions can be applied, and which can be produced at an approximately same cost as that of a normal ceramic. <P>SOLUTION: The piezoelectric element material is composed of a polycrystalline ceramic, and at least two peaks present in the particle size distribution of the ceramic particles. The maximum peak of the particle diameter is present within the range of 10-400 μm, and the number of the ceramic particles each having a particle diameter within half-value width of the maximum peak of the particle diameter is ≥10% of the number of total ceramic particles. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric element material applied to a transducer that performs energy conversion between pressure and electric power, such as an actuator or a sensor, and more particularly to a technique for improving piezoelectric characteristics while improving mechanical strength.

  Conventionally, a transducer is used as a drive source such as a fuel pump valve of an automobile, a clutch hydraulic valve, or an ink nozzle of an ink jet printer. In recent years, an acceleration sensor having a transducer is used for vehicle body control of an automobile, and the transducer is playing an important role in various technical fields. There are transducers composed of conductive / dielectric polymers, transducers composed of shape memory alloys, and transducers composed of piezoceramics. Among them, piezoceramics have been attracting attention in recent years because of their high response frequency and high output density. Piezoceramics include Pb-based materials composed of complex oxides of Pb and other metals and non-Pb-based materials such as barium titanate. Pb-based materials have good heat resistance and excellent piezoelectric characteristics. In addition, non-Pb systems that are currently provided do not perform as well as non-Pb systems, but establishment of technology is required as a future environmental measure. Here, piezoceramics have a property of generating a piezoelectric effect that generates electricity when pressure is applied and an inverse piezoelectric effect that generates distortion when voltage is applied. The piezoelectric effect is used for various sensors, and the reverse piezoelectric effect is used for various actuators.

  As a technique for improving the piezoelectric characteristics of piezoceramics, for example, as described in Patent Document 1, a technique for aligning ceramic particles using a technique called a template method, or as described in Patent Document 2 There is a technique for producing a single crystal piezo. However, each of these techniques requires a special process, so that the manufacturing cost is high and the components, elements, and compositions that can be manufactured are limited. In particular, single crystal piezos have a problem of low strength.

  On the other hand, Patent Document 3 proposes a piezoceramic having at least two peak of the particle size distribution of a piezoelectric film made of a polycrystal and having a large crystal grain size of 1000 to 2000 nm. Has been. Such piezoceramics have the advantage that the piezoelectric properties are improved by particles having a relatively large particle size.

JP 2004-300019 A (abstract) JP 2003-89599 A (abstract) JP 2002-84012 A (abstract)

However, the technique described in Patent Document 3 is intended to drive the ink nozzles of an ink jet printer, has a small amount of distortion for use in automobile actuators, and does not have sufficient characteristics for in-vehicle use. It was.
Accordingly, the present invention has the same strength as conventional ceramics while improving the piezoelectric characteristics including the amount of strain, has a wide range of applicable components, elements and compositions, and at the same cost as ordinary ceramics. An object of the present invention is to provide a piezoelectric element material that can be manufactured.

  The piezoelectric element material of the present invention is a piezoelectric element material composed of polycrystalline ceramics, wherein the particle size distribution of the ceramic particles has two or more peaks, and the maximum particle diameter peak is in the range of 10 to 400 μm. And the number of ceramic particles having a particle size within a half width of the peak of the maximum particle size is 10% or more of the total number of ceramic particles.

  FIG. 1 is a diagram showing the particle size distribution of ceramic particles in the present invention. As shown in FIG. 1, in the present invention, the particle size distribution of ceramic particles has two or more peaks. Here, the half width of the peak is defined as a particle diameter range Da to Db at two points a and b that take half the value of the polar (number) h in the particle diameter distribution curve.

  In the present invention, the peak of the maximum particle size is set to an extremely large range of 10 to 400 μm, and the large particle size has large polarization, so that the piezoelectric characteristics can be improved. In addition, since there is a peak with a small particle size, the mechanical strength can be maintained by filling the gaps between the large particles with the small particles. Moreover, since the piezoelectric element material of the present invention can be manufactured by a normal process of classifying and mixing ceramic particles, an increase in manufacturing cost can be suppressed. Furthermore, as long as normal firing is possible, there are no restrictions due to components, elements, and composition.

  Hereinafter, the best mode for carrying out the present invention will be described. The piezoelectric element material of the present invention includes a step of mixing raw material powder made of ceramic particles, a step of calcining the mixed raw material powder to form a dielectric, and a step of pulverizing the calcined dielectric powder. The step of firing the pulverized dielectric powder, the step of pulverizing the dielectric powder that has been baked and solidified, the step of classifying the pulverized dielectric powder, and the dielectric powder having a predetermined particle size range are mixed. It can be manufactured by a step, a step of forming the mixed dielectric powder into a green compact, and a step of firing the green compact. Hereinafter, the above steps will be described in order.

1. Mixing step Metal oxide powders such as PbO, NiO, Nb ₂ O ₃ , TiO ₂ , and ZrO ₂ are weighed at a predetermined ratio and mixed using a mortar, ball mill, or the like.

2. Calcination process The mixed raw material powder is filled in a container and heat treated to form a dielectric. In the calcining step, not all of the raw material powder is made dielectric, but is roughly made dielectric. For example, the calcining is held at about 1000 ° C. for 2 to 6 hours.

3. Crushing process The dielectric powder is hardened by calcining, and is pulverized using a mortar, a ball mill or the like. Thereby, the unreacted raw material powder completely reacts in the next main baking.

4). Main baking process The main baking process is a process in which unreacted raw material powder is reacted to form a dielectric completely. For example, the main baking is held at about 1200 ° C. for about 2 hours.

5). Pulverization process In the pulverization process, the dielectric powder is hardened by the main baking, and is pulverized using a mortar or a ball mill. Thereby, the next classification becomes possible.

6). Classification step The classification step is a step of dividing the dielectric powder into a desired particle size by sieving or the like. And it classifies so that the thing of the size mixed in the next mixing process may be obtained.

7). Mixing process The dielectric powder is selected from the particle sizes classified in the classification step, the particle size distribution of the ceramic particles has two or more peaks, and the maximum particle size peak is in the range of 10 to 400 μm. In addition, the ceramic particles are mixed so that the number of ceramic particles having a particle size within the half width of the peak of the maximum particle size is 10% or more of the total number of ceramic particles. Mixing is performed using a mortar or ball mill. Moreover, lubricants, such as zinc stearate, can also be mixed as needed. In addition, it is desirable that the minimum peak of the particle diameter is 0.5 to 3 μm.

8). Forming Step The forming step can be performed by the same method as a normal powder metallurgy method, and the mixed dielectric powder is filled in a press die and formed into a desired shape to obtain a green compact. Alternatively, it is also possible to use a method (CIP method) in which a liquid such as water is used as a pressurizing medium and a high isotropic pressure is applied to the green compact.

9. Firing step The firing step is a step in which the green compact is baked and solidified to form a dielectric ceramic. For example, the baking is performed at about 1200 to 1300 ° C. for about 1 to 2 hours. It is also possible to omit the main baking step and react the unreacted raw material powder in the baking step.

PbO, NiO, Nb ₂ O ₃ , TiO ₂ , ZrO ₂ metal oxide powders are weighed at a predetermined ratio, and mixing, calcination, pulverization, main baking, and pulverization processes are performed on these raw material powders. went. The obtained dielectric powder was classified and mixed. Also, a BaTiO ₃ powder was prepared, classified in the same manner, and mixed. When mixing the dielectric powder, the particle size distribution of the ceramic particles has two or more peaks, the maximum particle diameter peak is in the range of 10 to 400 μm, and the full width at half maximum of the maximum particle diameter peak is A powder in which the number of ceramic particles having a particle size within the range is 10% or more of the total number of ceramic particles and a powder deviating from the above range were prepared.

Tables 1 and 2 show the average particle diameter of the two peaks in the particle size distribution of the obtained dielectric powder, and the number and particle diameter of the particles present in the peak of the maximum particle diameter. Tables 1 and 2 also show the composition ratio of the dielectric powder. In Tables 1 and 2, PZN is Pb (Zn _1/3 Nb _2/3 ) O ₃ , PNN is Pb (Ni _1/3 Nb _2/3 ) O ₃ , and PZT is Pb (Zr _0.52 Ti _{0. 48} ) O ₃ , PT represents PbTiO ₃ , and BT represents BaTiO ₃ . Moreover, description of 0.5PNN-0.5PZT etc. shows that it is a mixed powder of 50 volume% PNN and 50 volume% PZT. In Tables 1 and 2, “localized particle size” refers to the number of peaks in the particle size distribution, and “average particle size” refers to the particle size at the peak. For example, in Table 1, No. 1, the peak of the particle size distribution shown in FIG. 1 is present at 15 μm and 400 μm, and 400 μm is the “maximum localized particle size”.

The obtained dielectric powder was press-molded into a disk shape having a diameter of 10 mm and a thickness of 1 mm at a pressure of 200 to 400 MPa, and the green compact was fired at a temperature of 1200 to 1300 ° C. for 1 to 2 hours. Further, the dielectric ceramic was polarized by applying a voltage of 2 to 3 kV / mm (DC) in the axial direction of the dielectric ceramic. The electromechanical coupling coefficient of the obtained piezoelectric element was measured. Here, the electromechanical coupling coefficient is a coefficient that represents the electrical-to-machine conversion capability of the transducer. If the amount of electrical input A that is converted to mechanical output is B, then (B / A) ^{1 /} It is represented by ² . Further, the relative dielectric constant (ε) of the piezoelectric element was measured. The above measurement results are shown in Tables 3 and 4. In addition, the dielectric constant was calculated by measuring the impedance of dielectric ceramics using an impedance analyzer (HP4294A, manufactured by Hewlett-Packard Company) (JIS R1627), and the electromechanical coupling coefficient was calculated (JIS R1600 4306). Further, the bending strength (MPa) of the obtained dielectric ceramic was measured.

  Next, the magnitude (g31) of the piezoelectric effect of the obtained piezoelectric element was measured. The piezoelectric effect is the magnitude of electric power that is output with respect to strain applied to the piezoelectric element. In addition, the distortion generated with respect to the electric field applied to the piezoelectric element was examined in the horizontal direction (d31), the vertical direction (d33), and the partial pressure direction (axial direction, d15) in plan view. The above measurement results are also shown in Tables 3 and 4.

  Sample No. 4, 8, 9, etc., the maximum particle diameter peak exists in the range of 10 to 400 μm, but the number of ceramic particles having a particle size within the half-value width of the maximum particle diameter peak is the total number of ceramic particles. Less than 10% of the number. For this reason, these comparative examples have mechanical strength equivalent to that of the example of the present invention, but all the piezoelectric properties such as relative dielectric constant are inferior to those of the example of the present invention. Sample No. In No. 24, since there was only one particle size distribution of the ceramic particles, the piezoelectric characteristics were considerably deteriorated. In addition, the piezoelectric characteristics are improved as the peak of the maximum particle diameter increases. Similar results were obtained with piezoelectric elements obtained from barium titanate powder.

  The present invention is applicable to transducers that perform energy conversion between pressure and electric power, such as actuators and sensors, and is particularly suitable for applications that require a large operating range such as fuel pump valves for automobiles. Can do.

It is a graph which shows the particle size distribution of ceramic particles.

Claims (2)

  A piezoelectric element material composed of polycrystalline ceramics, wherein the particle size distribution of the ceramic particles has two or more peaks, the maximum particle diameter peak is in the range of 10 to 400 μm, and the maximum A piezoelectric element material characterized in that the number of ceramic particles having a particle diameter within a half-value width of a particle diameter peak is 10% or more of the total number of ceramic particles.   A step of mixing raw material powders made of ceramic particles, a step of calcining the mixed raw material powder to form a dielectric, a step of grinding the calcined dielectric powder, and a dielectric having a predetermined particle size range In the method of manufacturing a piezoelectric element material comprising the steps of mixing powder, forming the mixed dielectric powder into a green compact, and firing the green compact. The ceramic particle size distribution has two or more peaks, the maximum particle diameter peak is in the range of 10 to 400 μm, and the ceramic particle has a particle size within the half width of the maximum particle diameter peak. A method for producing a piezoelectric element material, characterized in that the number is divided and mixed so as to be 10% or more of the total number of ceramic particles.

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