JP2009298621A - Piezoelectric material and piezoelectric element - Google Patents

Abstract

A piezoelectric material which does not contain lead, which is a harmful substance, is environmentally friendly and has excellent piezoelectric characteristics.
A piezoelectric material is represented by the following general formula (1). (1-x) BiFeO ₃ -xBaTiO ₃ (1) (where 0.70 ≦ x ≦ 0.90) This piezoelectric material has (1) a large piezoelectric constant, and (2) an electric field. It is excellent in all of the main characteristics required for the piezoelectric material that the displacement amount with respect to is linear and (3) the Curie point is high temperature.
[Selection] Figure 1

Description

  The present invention relates to a piezoelectric material which is environmentally friendly and has excellent piezoelectric characteristics, and a piezoelectric element having a piezoelectric body made of this material.

Piezoelectric materials are used in various electronic devices such as piezoelectric speakers and inkjet printer heads as piezoelectric actuators for electro-mechanical energy conversion. Currently, lead-based substances such as Pb (Zr, Ti) O ₃ (PZT) are widely used for these piezoelectric materials.

  However, due to environmental issues in recent years, the use of hazardous substances has been restricted as represented by the RoHS Directive (European Parliament and Council Directive on the Restriction of Use of Specific Hazardous Substances Included in Electrical and Electronic Equipment) centered on the EU Union. The development of the stipulated laws and regulations is progressing, and there is a demand for the development of piezoelectric materials that do not use lead, a hazardous substance.

  The present invention has been made in view of such circumstances, and provides a piezoelectric material which is environmentally friendly and has excellent piezoelectric characteristics.

Means for Solving the Problems and Effects of the Invention

The piezoelectric material of the present invention is represented by the following general formula (1).
(1-x) BiFeO ₃ —xBaTiO ₃ (1)
(However, 0.70 ≦ x ≦ 0.90.)

The piezoelectric material of the present invention does not contain lead and is environmentally friendly. Further, the main characteristics required for the piezoelectric material are 1) a large piezoelectric constant, (2) linearity in the amount of displacement with respect to the electric field, and (3) a high temperature of the Curie point. This piezoelectric material was experimentally confirmed to be excellent in all of these characteristics.
Therefore, according to the present invention, a piezoelectric material that is environmentally friendly and has excellent piezoelectric properties is provided.

  Hereinafter, the piezoelectric material of the present invention will be described in more detail.

1. Piezoelectric Material The piezoelectric material of the present invention is represented by the following general formula (1).
(1-x) BiFeO ₃ —xBaTiO ₃ (1)
(However, 0.70 ≦ x ≦ 0.90.)

  Specifically, the value of x is, for example, 0.70, 0.75, 0.80, 0.85, 0.90. The value of x may be within a range between any two of the numerical values exemplified here. This is because, within this range, the piezoelectric material has excellent piezoelectric characteristics as shown in the examples.

The method for producing the piezoelectric material of the present invention is not particularly limited. In one example, Bi ₂ O ₃ , α-Fe ₂ O ₃ , and BaTiO ₃ powders are weighed and mixed to have a desired chemical composition, and pelletized. It can be manufactured by repeating firing and pulverization. The firing temperature is not particularly limited as long as it is a temperature at which Bi ₂ O ₃ , α-Fe ₂ O ₃ , and BaTiO ₃ can be subjected to solid phase reaction, but 800 to 1000 ° C. is preferable. If the temperature is too high, a liquid phase appears and does not become a single phase. If the temperature is too low, the solid phase reaction may take too long. The reason for repeating the pelletization, firing, and pulverization is to make the composition uniform throughout the material and not leave any space in the material. This is because the electrical characteristics are not uniform if the composition is non-uniform or if a space remains in the material.

2. Piezoelectric Element When the piezoelectric material of the present invention is used, a piezoelectric element having excellent piezoelectric characteristics can be produced.
The piezoelectric element includes a piezoelectric body made of the above-described piezoelectric material and a pair of electrodes provided on the piezoelectric body. The pair of electrodes may be provided on two opposing surfaces of the piezoelectric body, or may be provided on one surface of the piezoelectric body separately from each other. This is because in either case, an electric field can be applied to the piezoelectric body by applying a voltage between the electrodes. The piezoelectric body is preferably a thin plate or a thin film.
The method for forming the piezoelectric body is not particularly limited. For example, the bulk sample manufactured by the method described in the above section “2. About manufacturing method” may be formed by thinning by polishing. A sample may be used as a target, and this target may be formed by ion sputtering. Moreover, you may form a piezoelectric material by heat-processing what apply | coated the precursor solution as described in Unexamined-Japanese-Patent No. 2007-287745. The electrode can be formed, for example, by sputtering or evaporating a metal such as gold.

  Examples of the present invention will be described below.

1. Sample preparation The sample used in the experiment was prepared by a solid phase reaction method using raw material powder Bi ₂ O ₃ , α-Fe ₂ O ₃ , and BaTiO ₃ as described below.
First, raw powder Bi ₂ O ₃ , α-Fe ₂ O ₃ (pretreated for 20 hours at 600 ° C.), BaTiO ₃ (purity 99.9%) were weighed and mixed at a stoichiometric ratio. . Thereafter, the sample was pelletized with a 10 mmφ die, and the pelletized sample was fired at 850 ° C. for 30 hours. Further, after pulverization and mixing, pelletized and fired at 880 ° C. for 30 hours. Finally, it was pelletized by the same procedure, fired at 950 to 1000 ° C. for 72 hours depending on the composition, and then annealed at 720 ° C. for 48 hours to obtain ceramic samples (samples 1 to 3 and comparative sample).
The value of x in the general formula (1) of each sample is as shown in Table 1. Samples 1 to 3 are examples of the present invention, and the comparative sample is a comparative example of the present invention.

2. Measurement of Piezoelectric Characteristics Piezoelectric characteristics of Sample 1, Sample 2, Sample 3, and Comparative Sample were measured by the following method.

Sample 1, Sample 2, Sample 3 and the comparative sample were polished to a thickness of about 200 μm, and electrodes of 1 mmφ were attached to the upper and lower surfaces of the pellet by gold sputtering.
Next, for each sample, a 10-Hz AC voltage was applied between the upper and lower electrodes using a ferroelectric property evaluation system (TOYO-6252 Rev. B), and the laser was changed using GRAPHTEC's MICROSCOPE SYSTEM while changing the voltage. Minute displacement was measured by Doppler method. The measurement was performed at room temperature.

The obtained measurement results are shown in FIGS. FIG. 1 is a graph showing the change in displacement with respect to the electric field from the outside for Samples 1 to 3, and FIG. 2 is a graph showing the change in displacement with respect to the electric field for the comparative sample. Table 2 shows the values of the piezoelectric constant d ₃₃ obtained for the samples 1 to 3.

Referring to Table 2, it can be seen that the piezoelectric constant d ₃₃ of Samples 1 to 3 is 86 to 107 (pm / V). PZT piezoelectric constant d ₃₃ of a typical piezoelectric material, since it is 100 to 200 in the vicinity of MPB, sample 1-3 is an embodiment of the present invention has a sufficient amount of distortion both practical I understood that.

  Further, comparing FIGS. 1 and 2, it can be seen that Samples 1 to 3, which are examples of the present invention, exhibit a distortion amount having better linearity with respect to the electric field than the comparative sample, which is a comparative example. From this, it can be seen that the piezoelectric material of the present invention is a piezoelectric material in which the amount of strain is easily controlled by an electric field and dielectric fatigue is not easily caused.

4). Measurement of relative permittivity The relative permittivity of Sample 1 and Sample 3 was measured by the following method.
Samples 1, 3 and the comparative sample were polished to a thickness of about 600 μm, and electrodes of 8 mmφ were attached to the upper and lower surfaces of the pellet by gold sputtering.
Next, the relative dielectric constant of each sample was measured. The relative dielectric constant was measured using an LCR meter (Agilent, HP-E4980A), and the measurement temperature was changed using an infrared furnace. The measurement was performed from room temperature to 300 ° C. in increments of 3 ° C. during the temperature raising process, and the measurement frequency was 1 MHz.
The measurement results are shown in FIGS. 3 and 4 are graphs showing the measurement results of the temperature change of the relative dielectric constant for Sample 1 and Sample 3, respectively.
3 and 4, it can be seen that the Curie points of Sample 1 and Sample 3 are 140 ° C. and 120 ° C., respectively.
Since the Curie point of barium stannate titanate (Ba (Sn, Ti) O ₃ ), which has been attracting attention in recent years, is around room temperature, the piezoelectric material of the present invention is superior in temperature characteristics to BST and has a wide temperature range. It can be seen that it can be used.

5. Electromechanical coupling constant The electromechanical coupling coefficient k is expressed by k ² ≈d ² / ε (d: piezoelectric constant, ε: relative dielectric constant). The piezoelectric constant d of Ba (Sn, Ti) O ₃ is about 270 (pm / V), the relative dielectric constant is about 1000 for the piezoelectric material of the present invention, and about 10,000 for Ba (Sn, Ti) O ₃ (Manling Bao , Weidong Li, et al J. Materials Science 28 6617 (1993)), d ² / ε is about 7.3 for Ba (Sn, Ti) O ₃ and about 10 for the piezoelectric material of the present invention. Become. Therefore, it can be seen that the piezoelectric material of the present invention is higher than the Ba (Sn, Ti) O _{3 in} terms of conversion efficiency between mechanical energy and electric energy.

6). Summary From the above, Samples 1 to 3 as examples of the present invention have (1) a large piezoelectric constant, (2) a strain amount having a good linearity with respect to an electric field, and (3) a high Curie point. (4) It has been found that it has an excellent characteristic that the electromechanical coupling constant is large. This experimentally revealed that the piezoelectric material of the present invention has excellent piezoelectric characteristics.

It is a graph which shows the change of the displacement amount with respect to the electric field about the samples 1-3 which are the Examples of this invention. It is a graph which shows the change of the displacement amount with respect to the electric field about the comparative sample which is a comparative example of this invention. It is a graph which shows the relationship between the frequency about the sample 1 which is an Example of this invention, and a dielectric constant or a dielectric loss tangent. It is a graph which shows the relationship between the frequency about the sample 3 which is an Example of this invention, and a dielectric constant or a dielectric loss tangent.

Claims (2)

A piezoelectric material represented by the following general formula (1).
(1-x) BiFeO ₃ —xBaTiO ₃ (1)
(However, 0.70 ≦ x ≦ 0.90.) A piezoelectric element comprising a piezoelectric body made of the piezoelectric material according to claim 1 and a pair of electrodes provided on the piezoelectric body.

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