Information
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Patent Application
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20020049130
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Publication Number
20020049130
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Date Filed
August 28, 200123 years ago
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Date Published
April 25, 200222 years ago
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Inventors
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Original Assignees
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CPC
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US Classifications
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International Classifications
Abstract
A piezoelectric ceramic composition is provided that does not contain Pb, and yet has a large electromechanical coupling coefficient in comparison with a bismuth layered compound, as well as a piezoelectric ceramic element using the composition. This piezoelectric ceramic composition includes at least the elements Ag, Li, Nb, and O, and has an electromechanical coupling coefficient k33 of not less than about 20%.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a piezoelectric ceramic composition and a piezoelectric ceramic element using the composition. More particularly, the present invention relates to a piezoelectric ceramic composition useful as a material for piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic resonators, and to a piezoelectric ceramic element using the composition.
[0003] 2. Description of the Related Art
[0004] Conventionally, piezoelectric ceramic compositions comprising lead titanate zirconate (Pb(TixZr1−x)O3) or lead titanate (PbTiO3) as a main component are widely used for manufacturing piezoelectric elements such as piezoelectric ceramic filters. Recently, piezoelectric ceramic compositions comprising a bismuth layered compound such as CaBi4Ti4O15 as a main component have also been developed.
[0005] Pb, however, is suspected as a material which might cause environmental problems and affects human bodies. On the other hand, piezoelectric ceramics comprising bismuth layered compounds as the main components are not widely used in practice since the electromechanical coupling coefficients k33 are as small as less than 20%.
SUMMARY OF THE INVENTION
[0006] Therefore, it is an object of the present invention to provide a piezoelectric ceramic composition which does not contain Pb and which has an electromechanical coupling coefficient larger than that of a bismuth layered compound, and to provide a piezoelectric ceramic element using the composition.
[0007] A piezoelectric ceramic composition according to the present invention is characterized in that it comprises at least the elements Ag, Li, Nb, and O, and has an electromechanical coupling coefficient k33 of not less than about 20%.
[0008] It is also characterized in that it comprises a main component represented by the general formula (Ag1−xLix)(Nb1−yTay)O3, wherein 0.075≦x<0.40 and 0≦y<0.20. In one embodiment, y−0 and the main component corresponds to (Ag1−xLix)NbO3. In another embodiment, y is greater than 0 and the main component corresponds to (Ag1−xLix)(Nb1−yTay)O3.
[0009] Furthermore, it is preferable that the composition comprises at least one of a manganese oxide and a silicon oxide as an auxiliary component. It is more preferable that the manganese oxide should be contained in an amount of not more than about 5 parts by weight based on 100 parts by weight of the main component, and that the silicon oxide should be contained in an amount of not more than about 5 parts by weight based on 100 parts by weight of the main component.
[0010] Furthermore, a piezoelectric ceramic element according to the present invention comprises a piezoelectric ceramic made from the piezoelectric ceramic composition according to the present invention, and an electrode formed on the piezoelectric ceramic.
[0011] In the general formula for the piezoelectric ceramic composition according to the present invention, a range of x<0.075 is not preferable since the transition temperature is decreased, across which a ferroelectric phase acting as a piezoelectric material turns into a paraelectric phase or an antiferroelectric phase which does not act as a piezoelectric material, with the result that there will be problems regarding the temperature stability of the elements composed of the piezoelectric ceramic composition. Also, when 0.40≦x, the resonance frequency constant will be smaller than 2,000 Hz/m, and polarization will not occur easily. When y is not less than 0.20, the transition temperature will be decreased, too. Accordingly, the ranges of 0.075≦x<0.40 and 0≦y<0.20 are required in the present invention.
[0012] Furthermore, in the present invention, the baking temperature can be decreased by adding a manganese oxide or a silicon oxide to the main component. It is to be noted that it is preferable that the manganese oxide should be contained in an amount of not more than about 5 parts by weight based on 100 parts by weight of the main component, and that the silicon oxide should be contained in an amount of not more than about 5 parts by weight based on 100 parts by weight of the main component, so as not to degrade the properties that are achieved when no such materials are added.
[0013] Furthermore, the piezoelectric ceramic composition according to the present invention may be a solid solution, a mixture, a polycrystal or a single crystal.
[0014] The above-described objects, other objects, features, and advantages of the present invention will become more apparent from the following detailed explanations of the embodiments when taken in conjunction with the accompanying drawings, tables, and examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
FIG. 1 is a perspective view showing an example of a piezoelectric ceramic resonator according to the present invention; and
[0016]
FIG. 2 is a cross-sectional illustrative view of the piezoelectric ceramic resonator shown in FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0017] Although the present invention will be described with reference to the following drawings, tables and examples, it is to be understood that the invention is not limited to the precise embodiments described below, and various changes and modifications may be made to various usages and conditions without departing from the spirit and scope of the invention as described in the claims that follow.
[0018] The piezoelectric ceramic composition according to the present invention can be manufactured in the same way as is applied to manufacturing of conventional ferroelectric materials and dielectric materials. For example, specific amounts of Ag2O, Nb2O5, Ta2O5 and Li2CO3 are first weighed out and blended together in a solvent such as water or ethanol, using zirconia balls or similar media for from 4 to 24 hours. A dispersing agent such as a sorbitan ester may be added for achieving more homogeneous blending. After that, the slurry thus blended is dried and then subjected to calcination in an oxidizing atmosphere at from 800 to 1,100° C. for from 1 to 24 hours using a common electric furnace. The calcined product is crushed and blended with a binder such as polyvinyl alcohol in a solvent such as water or ethanol, using zirconia balls or similar media and then dried. The powder thus obtained by drying is subjected to uniaxial pressing to form square plaque samples having a size of 12 mm in length, 12 mm in width and 3 mm in thickness. The samples are further subjected to baking in an oxidizing atmosphere at from 950 to 1,200° C. for from 3 to 10 hours. Piezoelectric ceramics from the piezoelectric ceramic composition according to the present invention can be manufactured by these operations. The present invention will be further explained, based on the examples below.
EXAMPLE 1
[0019] First, powders of Ag2O, Nb2O5, Ta2O5 and Li2CO3 were weighed out and blended together to prepare mixtures having specific compositions according to the values for x and y listed in Table 1. The mixtures were then subjected to calcination in an oxidizing atmosphere at from 850 to 1,100° C. for 10 hours, using an electric furnace. The powders thus obtained were crushed and blended with polyvinyl alcohol such that the polyvinyl alcohol was in an amount of 5 parts by weight based on 100 part by weight of each powder. Then they were dried and subjected to unaxial pressing (10 ton/cm2) to form square plaque samples having a size of 12 mm in length, 12 mm in width, and about 2.5 mm in thickness. The samples thus obtained were baked in an oxidizing atmosphere at the temperatures listed in Table 1.
1TABLE 1
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Sample No.xyBaking temperature (° C.)
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*10.0000.0001,040
**20.0250.0001,040
**30.0500.0001,040
40.0750.0001,040
50.1000.0001,040
60.1250.0001,040
70.1500.0001,020
80.2000.0001,020
90.3000.0001,020
**100.4000.0001,020
110.1000.0501,020
120.1000.1001,040
**130.1000.2001,120
140.0750.0501,020
150.1500.1001,040
**160.4000.1001,040
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[0020] In all of the Tables herein, the asterisk * indicates that the compositions are out of the scope of the present invention and the mark ** indicates that the compositions are out of the scopes of some of the preferred embodiments of the present invention.
[0021] After that, a Ag paste was applied to the surfaces of the plaque samples, and the samples were baked at 800° C. Then, they were subjected to a polarization treatment by applying a direct-current voltage of from 50 kV/cm to 200 kV/cm in an insulating oil bath at from 100 to 150° C. for from 3 to 10 minutes. Next, square pillars having a size of 2 mm×2 mm×3 mm were cut out using a dicing machine. The samples thus obtained were subjected to measurements of dielectric constant, electromechanical coupling coefficient k33 for the thickness vibration, piezoelectric constant d33 for the thickness vibration, resonance frequency constant N for the thickness vibration, and transition temperature. The results are shown in Table 2. From Table 2, it is understood that the compositional range according to the present invention provides a good electromechanical coupling coefficient k33 of not less than 20%, and a transition temperature of not less than 200° C.
2TABLE 2
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Resonance
CouplingPiezoelectricfrequencyTransition
SampleDielectriccoefficient k33constant d33constanttemperature
No.constant(%)(pC/N)(Hz/m)(° C.)
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*1MeasurementMeasurementMeasurementMeasurement 70
failedfailedfailedfailed
**218021181,873 70
**319441522,139150
425341552,089210
530441552,076290
628435502,065310
726327412,073310
824221272,122310
923225352,239320
**1017922311,956320
1115944532,141260
1215445532,149250
**1317842502,188160
1415339432,075230
1515445532,149210
**1613228382,052 80
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EXAMPLE 2
[0022] In a similar way to that applied to Example 1, powders of Ag2O, Nb2O5, Ta2O5 and Li2CO3 were first weighed out and blended together to prepare mixtures having specific compositions according to the values for x and y listed in Table 3. The mixtures were then subjected to calcination in an oxidizing atmosphere at from 900 to 1,200° C. for 10 hours using an electric furnace. Powders of MnCO3 and/or SiO2 in an amount shown in Table 3 was added to the powders, and then the powders were blended with polyvinyl alcohol such that the polyvinyl alcohol was in an amount of 5 parts by weight based on 100 parts by weight of each powder. Then they were dried and subjected to uniaxial pressing (10 ton/cm2) to form square plaque samples having a size of 12 mm in length, 12 mm in width and about 2.5 mm in thickness. The samples thus obtained were baked in an oxidizing atmosphere at the temperatures listed in Table 3. After that, a Ag paste was applied to the surfaces of the plaque samples, and the samples were baked at 800° C.
3TABLE 3
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Amount ofAmount of
BakingMnCO3 addedSiO2 added
Sampletemperature(parts by(parts by
No.xy(° C.)weight)weight)
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170.0750.0001,0200.20.0
180.0750.0001,0002.00.0
190.1000.0001,0003.00.0
200.1000.0009805.00.0
**210.1500.0009806.00.0
220.0750.0001,0200.00.2
230.0750.0001,0200.02.0
240.1000.0001,0000.03.0
250.1000.0009800.05.0
**260.1500.0009800.06.0
270.1250.0009800.20.2
280.1250.0009803.02.0
290.1000.0509803.00.0
300.1000.1001,0000.02.0
**310.1000.0509806.00.0
**320.1000.1001,0000.06.0
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[0023] After that, they were subjected to a polarization treatment by applying a direct-current voltage of from 50 kV/cm to 200 kV/cm in an insulating oil bath at from 100 to 150° C. for from 3 to 10 minutes. Next, square pillars having a size of 2 mm×2 mm×3 mm were cut out, using a dicing machine. The samples thus obtained were subjected to measurements of dielectric constant, electromechanical coupling coefficient k33 for the thickness vibration, piezoelectric constant d33 for the thickness vibration, resonance frequency constant N for the thickness vibration, and transition temperature. The results are shown in Table 4. As shown in Table 4, by adding MnCO3 and/or SiO2, it is possible to obtain a piezoelectric ceramic composition having a good electromechanical coupling coefficient k33 of not less than 20%, which is equivalent to that of a sample without the addition of such a material, having a transition temperature of not less than 200° C. and having a low baking temperature.
4TABLE 4
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Resonance
CouplingPiezoelectricfrequencyTransition
SampleDielectriccoefficientconstant d33constanttemperature
No.constantk33 (%)(pC/N)(Hz/m)(° C.)
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1725940532,053220
1826342572,073215
1931040542,081290
2031343552,075295
**2129222341,756305
2225543572,016210
2325841582,063210
2431645562,066295
2531442532,032290
**2628523361,873300
2729438492,073315
2829639532,072310
2917542472,103255
3016341462,089245
**3118632421,898255
**3217734401,946250
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[0024]
FIG. 1 is a perspective view showing an example of a piezoelectric ceramic element according to the present invention. FIG. 2 is a cross-sectional view thereof. The piezoelectric ceramic element shown in FIGS. 1 and 2 is a piezoelectric ceramic resonator 10. The piezoelectric ceramic resonator 10 comprises a piezoelectric ceramic 12 in a cubic shape, for example. The piezoelectric ceramic 12 comprises two sheets of piezoelectric ceramic layers 12a and 12b. These piezoelectric ceramic layers 12a and 12b are composed of a piezoelectric ceramic composition according to the above-described present invention, and are laminated and consolidated to form a unitary structure. These piezoelectric ceramic layers 12a and 12b are polarized along the same thickness direction as shown by the arrows in FIG. 2.
[0025] A vibrating electrode 14a in a circular shape, for example, is placed in between the piezoelectric ceramic layers 12a and 12b, and at the center of the interface. A lead electrode 16a in a T shape, for example, is formed connecting the vibrating electrode 14a and one edge surface of the piezoelectric ceramic 12. A vibrating electrode 14b in a circular shape, for example, is placed at the center of the surface of the piezoelectric ceramic layer 12a. A lead electrode 16b in a T shape, for example, is formed connecting the vibrating electrode 14b and the other edge surface of the piezoelectric ceramic 12. Furthermore, a vibrating electrode 14c in a circular shape, for example, is placed at the center of the surface of the piezoelectric ceramic layer 12b. A lead electrode 16c in a T shape, for example, is formed connecting the vibrating electrode 14c and the other edge surface of the piezoelectric ceramic 12.
[0026] Thereafter, the lead electrode 16a is connected to an external electrode 20a via a lead wire 18a, and the lead electrode 16b and 16c are connected to another external electrode 20b via another lead wire 18b.
[0027] Hereupon, it is to be noted that the present invention is also applicable to various piezoelectric ceramic resonators other than the above-described piezoelectric ceramic resonator 10 as well as other piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators.
[0028] According to the present invention, a piezoelectric ceramic composition can be obtained, which provides a large (not less than about 20%) electromechanical coupling coefficient k33 in comparison with a bismuth layered compound, without containing Pb, and can therefore be of practical use. Furthermore, by adding at least one of a manganese oxide and a silicon oxide as an auxiliary component to the main component of the piezoelectric ceramic composition according to the present invention, a lower baking temperature can be realized, without degrading various properties such as dielectric constant, electromechanical coupling coefficient k33 for the thickness vibration, piezoelectric constant d33 for the thickness vibration, resonance frequency constant N for the thickness vibration and transition temperature.
Claims
- 1. A piezoelectric ceramic composition comprising at least the elements Ag, Li, Nb and O, and having an electromechanical coupling coefficient k33 of not less than about 20%.
- 2. A piezoelectric ceramic composition according to claim 1, comprising at least one of a manganese oxide and a silicon oxide as an auxiliary component.
- 3. A piezoelectric ceramic composition according to claim 2, wherein said manganese oxide is in an amount of not more than about 5 parts by weight based on 100 parts by weight of said main component, and wherein said silicon oxide is in an amount of not more than about 5 parts by weight based on 100 parts by weight of said main component.
- 4. A piezoelectric ceramic composition according to claim 1 in which the main component is represented by the general formula (Ag1−1Lix)(Nb1−1Tay)O3, wherein 0.075≦x<0.40 and 0≦y<0.20.
- 5. A piezoelectric ceramic composition according to claim 4, comprising at least one of a manganese oxide and a silicon oxide as an auxiliary component.
- 6. A piezoelectric ceramic composition according to claim 5, wherein said manganese oxide is in an amount of not more than about 5 parts by weight based on 100 parts by weight of said main component, and wherein said silicon oxide is in an amount of not more than about 5 parts by weight based on 100 parts by weight of said main component.
- 7. A piezoelectric ceramic composition according to claim 2 in which the main component is main component represented by the general formula (Ag1−xLix)NbO3, wherein 0.075≦x<0.40.
- 8. A piezoelectric ceramic composition according to claim 7, comprising at least one of a manganese oxide and a silicon oxide as an auxiliary component.
- 9. A piezoelectric ceramic composition according to claim 8, wherein said manganese oxide is in an amount of not more than about 5 parts by weight based on 100 parts by weight of said main component, and wherein said silicon oxide is in an amount of not more than about 5 parts by weight based on 100 parts by weight of said main component.
- 10. A piezoelectric ceramic composition according to claim 2 in which the main component is represented by the general formula (Ag1−xLix)(Nb1−yTay)O3, wherein 0.075≦x<0.40 and 0<y<0.20.
- 11. A piezoelectric ceramic composition according to claim 10, comprising at least one of a manganese oxide and a silicon oxide as an auxiliary component.
- 12. A piezoelectric ceramic composition according to claim 11, wherein said manganese oxide is in an amount of not more than about 5 parts by weight based on 100 parts by weight of said main component, and wherein said silicon oxide is in an amount of not more than about 5 parts by weight based on 100 parts by weight of said main component.
- 13. A piezoelectric ceramic comprising a polarized piezoelectric ceramic composition according to claim 10.
- 14. A piezoelectric ceramic comprising a polarized piezoelectric ceramic composition according to claim 7.
- 15. A piezoelectric ceramic comprising a polarized piezoelectric ceramic composition according to claim 4.
- 16. A piezoelectric ceramic comprising a polarized piezoelectric ceramic composition according to claim 1.
- 17. A piezoelectric ceramic element comprising a piezoelectric ceramic according to claim 16 having an electrode thereon.
- 18. A piezoelectric ceramic element comprising a piezoelectric ceramic according to claim 15 having an electrode thereon.
- 19. A piezoelectric ceramic element comprising a piezoelectric ceramic according to claim 14 having an electrode thereon.
- 20. A piezoelectric ceramic element comprising a piezoelectric ceramic according to claim 13 having an electrode thereon.
Priority Claims (1)
Number |
Date |
Country |
Kind |
2000-257883 |
Aug 2000 |
JP |
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