Piezoelectric ceramic composition and piezoelectric element using the piezoelectric ceramic composition

Abstract: The present invention is to provide a piezoelectric ceramic composition containing a lead titanate, having an excellent temperature stability of the resonance frequency, suitable for the application in a filter, a vibrator, or the like, and a piezoelectric element using the piezoelectric ceramic composition. A piezoelectric substrate comprising a ceramic material containing PbTiO 3 is provided with vibrating electrodes on the front and rear surfaces. The ceramic material containing PbTiO 3 contains not less than 0.1% by weight but not more than 3.0% by weight of Mn based on MnCO 3 as the sub component in the main component having a composition satisfying 0.02 ≤ x ≤ 0.16 and 0.15 ≤ y ≤ 0.50 of the general formula Pb 1-1.5x Nd x [(In 1/2 Nb 1/2 ) y Ti 1-y ]O 3 .

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition and a piezoelectric element using the piezoelectric ceramic composition. 2. Description of the Related Art Conventionally, a piezoelectric ceramic composition containing a lead titanate (PbTiO 3 ) is known. Since a piezoelectric ceramic composition containing a lead titanate has a low dielectric constant and a small particle size, it is suitable for the use in a high frequency range. Moreover, it has excellent characteristics such as ability in restraining sub-resonance owing to a large piezoelectric anisotropy, durability in use at a high temperature owing to a high Curie point, or the like. Therefore, use of a piezoelectric ceramic containing a lead titanate is required in the field of filters, vibrators, or the like, to be used in a high frequency range. However, a piezoelectric ceramic containing a lead titanate has disadvantages such as difficulty in obtaining a dense sintered compact having a large mechanical strength due to difficulty in sintering, and difficulty in polarization. In order to solve the problems, for example, a piezoelectric ceramic composition containing a lead titanate obtained by partially substituting Pb of PbTiO 3 by La and adding a Mn compound such as MnCO 3 , or the like has been used. The piezoelectric ceramic has characteristics such as a good sintering property and capability of a polarization treatment at a high temperature in a high electric field. However, a problem is involved in that the piezoelectric ceramic has a poor temperature coefficient of the resonance frequency and thus when it is used in a filter or a vibrator, the passing frequency or the oscillating frequency changes drastically according to the temperature. Therefore, it has been difficult to adopt a ceramic containing lead titanate in a filter or a vibrator, which is required to have a high accuracy. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a piezoelectric ceramic composition containing a lead titanate, having excellent temperature stability of the resonance frequency, suitable for the application in a filter, a vibrator, or the like, and a piezoelectric element using the piezoelectric ceramic composition. In order to achieve the above-mentioned object, a piezoelectric ceramic composition according to the present invention is represented by the general formula Pb 1-1.5x Nd x [(In 1/2 Nb 1/2 ) y Ti 1-y ]O 3 , wherein not less than 0.1% by weight but not more than 3.0% by weight of Mn based on MnCO 3 is contained as the sub component in the main component having a composition satisfying 0.02 ≤ x ≤ 0.16 and 0.15 ≤ y ≤ 0.50. According to the above-mentioned configuration, a piezoelectric ceramic composition having a good temperature coefficient of the resonance frequency can be obtained. Moreover, a piezoelectric element using the piezoelectric ceramic composition with the above-mentioned configuration can restrain the change of the passing frequency, the oscillating frequency, or the like, derived from the temperature. The amount x of substituting Nd by Pb here is set to be 0.02 ≤ x ≤ 0.16 because the sintering property of the ceramic cannot be good and the improving effect of the temperature coefficient of the resonance frequency is small if x < 0.02, but the Curie temperature is drastically deteriorated so as not to be durable in a high temperature if 0.16 < x. The range of y is set to be 0.15 ≤ y ≤ 0.50 because the temperature coefficient of the resonance frequency is poor if y < 0.15, but the Curie temperature is drastically deteriorated so as not to be durable in a high temperature if 0.50 < y. The amount of Mn as the sub component is preferably not less than 0.1% by weight but not more than 3.0% by weight based on MnCO 3 . This is because the mechanical quality coefficient Qm is small so that it is not suitable for the application in a vibrator, a filter, or the like, with less than 0.1% by weight, but the insulating property of the ceramic is deteriorated so that it cannot be applied with a polarization treatment and thus it cannot be used as a piezoelectric ceramic with more than 3.0% by weight. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an exploded perspective view showing one embodiment of a piezoelectric element according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT Hereinafter, an embodiment of a piezoelectric ceramic composition and a piezoelectric element using the piezoelectric ceramic composition according to the present invention will be explained with reference to the accompanied drawing. As shown in FIG. 1, a piezoelectric element to be used as a piezoelectric filter comprises a piezoelectric substrate 1, an insulating container 10 accommodating the piezoelectric substrate 1, and a sealing lid 20. The piezoelectric substrate 1 has a substantially rectangular shape. The piezoelectric substrate 1 is provided with vibrating electrodes 2a, 2b, vibrating electrodes 3a, 3b on the front surface, and vibrating electrodes 2c, 3c on the rear surface. The vibrating electrodes 2a, 3b are connected electrically with lead electrodes 4a, 4b provided on the end parts of the front surface of the piezoelectric substrate 1, respectively. The vibrating electrodes 2b, 3a are connected electrically therewith via a conductor path. The lead electrodes 4a, 4b are arranged on both end parts of the substrate 1, respectively. furthermore, the vibrating electrodes 2c and 3c are connected electrically via a conductor path provided at the rear center part of the substrate 1. The piezoelectric substrate 1 comprises a ceramic material containing PbTiO 3 . The vibrating electrodes 2a to 3c and the lead electrodes 4a, 4b comprise Ag, Ag-Pd, Ni, Cu, or the like. The piezoelectric substrate 1 generates the thickness longitudinal vibration by the vibrating electrodes 2a, 2b, 2c and the vibrating electrodes 3a, 3b, 3c. The insulating container 10 has a concave part 10a, with notches 11 provided at both end parts of the concave part 10a. A base 12 is provided at the bottom surface center part of the concave part 10a. The piezoelectric substrate 1 is guided by the notches 11 so as to be accommodated horizontally long sideways for being supported by the notches 11 and the base 12 without contacting with the bottom surface of the concave part 10a. The three parts, that is, the parts of the notches 11 and the base 12 of the container 10 are applied with a paste conductive adhesive so that the piezoelectric substrate 1 and the container 10 are fixed and connected electrically via the conductive adhesive. That is, lead electrodes 16, 17, 18 are formed at both end parts and the center part of the container 10 by sputtering, deposition, or the like. The lead electrodes 16, 17 elongate from the notch 11 parts, respectively, and the lead electrode 18 elongates from the base 12 part. The vibrating electrode 2a is connected electrically with the lead electrode 16 of the container 10 via the lead electrode 4a and the conductive adhesive. The vibrating electrode 3b is connected electrically with the lead electrode 17 of the container 10 via the lead electrode 4b and the conductive adhesive. The vibrating electrodes 2c, 3c are connected electrically with the lead electrode 18 of the container 10 via the conductive adhesive. The sealing lid 20 is provided with conductors 21, 22, 23 at both end part and the center part by sputtering, deposition, or the like. The sealing lid 20 is fixed to the open end face of the container 10 with an adhesive. Accordingly, the piezoelectric substrate 1 is accommodated in the sealed vibrating space provided by the container 10 and the sealing lid 20. The composition of the piezoelectric substrate 1 will be explained. As the materials of the piezoelectric substrate 1, Pb 3 O 4 , Nd 2 O 3 , In 2 O 3 , Nb 2 O 5 , TiO 2 , MnCO 3 were used. Other oxides of Pb, Nd, In, Nb, Ti, Mn, or a compound finally to be an oxide can also be used as a material. The above-mentioned materials measured so as to have the compositions shown in Tables 1 to 3 were mixed and pulverized by the wet process, and calcined at 750°C to 950°C for 1 to 4 hours. The obtained calcined powders were pulverized with an organic binder, and press-molded with a 1 ton/cm 2 pressure. The molded products were baked at 1,050°C to 1,250°C for 1 to 4 hours so as to obtain sintered compacts. After forming an electrode, the sintered compacts were polarized by applying a 3 to 5 kV/mm electric field for 10 to 30 minutes in a silicone oil of 100°C, and evaluated. The electric mechanical coupling coefficient k t (%) at the time of the thickness longitudinal vibration, the mechanical quality coefficient Qm, the Curie temperature Tc (°C), and the temperature coefficient of the resonance frequency F-TC (ppm/°C) are shown in Tables 1 to 3. Those marked with * at the specimen number are comparative examples outside the range of the present invention. Specimen number Nd substitution amount x In 1/2 Nb 1/2 substitution amount y MnCO 3 content (% by weight) k t (%) Q m T c (°C) F-TC (ppm/°C) * 1 0.10 0.20 0.0 41 110 350 10 * 2 0.10 0.00 0.1 37 650 380 -55 * 3 0.02 0.01 0.1 38 610 400 -49 * 4 0.10 0.01 0.1 39 600 370 -46 * 5 0.16 0.01 0.1 39 590 340 -38 * 6 0.00 0.15 0.1 29 230 390 -62 7 0.02 0.15 0.1 38 540 380 -34 8 0.10 0.15 0.1 40 550 360 -9 9 0.16 0.15 0.1 42 610 300 -5 * 10 0.18 0.15 0.1 41 590 280 12 * 11 0.00 0.20 0.1 30 290 380 -59 12 0.02 0.20 0.1 39 550 370 -33 13 0.10 0.20 0.1 41 540 350 5 14 0.16 0.20 0.1 43 560 290 9 * 15 0.18 0.20 0.1 42 560 280 15 * 16 0.00 0.35 0.1 31 210 360 -44 17 0.02 0.35 0.1 42 590 350 -30 18 0.10 0.35 0.1 41 540 320 10 19 0.16 0.35 0.1 44 550 290 10 * 20 0.18 0.35 0.1 44 520 260 40 21 0.02 0.50 0.1 42 500 330 -10 22 0.10 0.50 0.1 43 480 290 11 23 0.16 0.50 0.1 44 510 290 14 * 24 0.10 0.60 0.1 45 450 280 45 Specimen number Nd substitution amount x In 1/2 Nb 1/2 substitution amount y MnCO 3 content (% by weight) k t (%) Q m T c (°C) F-TC (ppm/°C) * 25 0.10 0.00 1.0 36 2010 380 -55 * 26 0.02 0.01 1.0 38 2030 400 -50 * 27 0.10 0.01 1.0 38 1980 370 -45 * 28 0.16 0.01 1.0 41 2000 370 -40 * 29 0.00 0.15 3.0 36 1810 400 -66 30 0.02 0.15 3.0 40 2010 380 -33 31 0.10 0.15 3.0 41 1910 360 -12 32 0.16 0.15 3.0 40 1920 300 -10 * 33 0.18 0.15 3.0 39 2000 280 10 * 34 0.00 0.20 1.0 39 1820 390 -60 35 0.02 0.20 1.0 40 2030 370 -30 36 0.10 0.20 1.0 42 1990 350 2 37 0.16 0.20 1.0 42 2040 290 10 * 38 0.18 0.20 1.0 42 2100 280 14 * 39 0.00 0.35 3.0 39 1870 370 -50 40 0.02 0.35 3.0 41 1990 350 -22 41 0.10 0.35 3.0 43 2000 320 8 42 0.16 0.35 3.0 43 1920 290 13 * 43 0.18 0.35 3.0 44 1940 260 20 44 0.02 0.50 1.0 41 1940 330 -21 45 0.10 0.50 1.0 43 1960 290 9 46 0.16 0.50 1.0 45 1960 290 14 * 47 0.10 0.60 1.0 44 1900 260 8 Specimen number Nd substitution amount x In 1/2 Nb 1/2 substitution amount y MnCO 3 content (% by weight) k t (%) Q m T c (°C) F-TC (ppm/°C) * 48 0.10 0.00 3.0 37 2110 380 -52 * 49 0.02 0.01 3.0 38 2040 400 -49 * 50 0.10 0.01 3.0 39 2060 370 -45 * 51 0.16 0.01 3.0 39 2010 340 -39 * 52 0.00 0.15 3.0 27 1980 390 -66 53 0.02 0.15 3.0 40 2020 380 -36 54 0.10 0.15 3.0 41 2060 360 -10 55 0.16 0.15 3.0 42 2010 300 -8 * 56 0.18 0.15 3.0 44 2050 280 10 * 57 0.00 0.20 3.0 28 2000 380 -62 58 0.02 0.20 3.0 40 1980 370 -35 59 0.10 0.20 3.0 42 1950 350 7 60 0.16 0.20 3.0 43 1980 290 8 * 61 0.18 0.20 3.0 42 2060 270 12 * 62 0.00 0.35 3.0 39 2060 360 -50 63 0.02 0.35 3.0 40 2080 350 -35 64 0.10 0.35 3.0 41 2110 370 10 65 0.16 0.35 3.0 41 2000 290 11 * 66 0.18 0.35 3.0 40 2050 260 16 67 0.02 0.50 3.0 41 2050 330 -25 68 0.10 0.50 3.0 45 2100 290 12 69 0.16 0.50 3.0 44 1980 290 14 * 70 0.10 0.60 3.0 44 1990 260 15 Since the specimen 1 not containing the sub component MnCO 3 , which is outside the range of the present invention, has a 200 or less mechanical quality coefficient Qm, it is not suitable for the application in a filter, a vibrator, or the like. Moreover, if the sub component MnCO 3 content is increased to 5% by weight, the insulating property of the sintered compact is deteriorated so that the polarization cannot be applied. Therefore, in the present invention, the content of the sub component MnCO 3 is defined to be not less than 0.1% by weight but not more than 3.0% by weight, wherein a preferable mechanical quality coefficient Qm can be obtained as well as the polarization operation can be conducted easily. Moreover, as in the specimens 10, 15, 20, 33, 38, 43, 56, 61, and 66, if the amount x of substituting Pb by Nd is increased to 0.18, which is outside the range of the present invention, the Curie temperature is lowered to 280°C or less. If the Curie temperature is 280°C or less, the piezoelectric property of the ceramic is drastically deteriorated by the reflow at the time of mounting an element utilizing a piezoelectric ceramic, such as a filer, a vibrator, or the like, and thus it is not preferable. On the other hand, if the amount x of substituting Pb by Nd is 0.00 (the specimens 6, 11, 16, 21, 34, 39, 52, 57, and 62), the temperature coefficient of the resonance frequency F-TC is deteriorated beyond -37 ppm/°C, it is not suitable for the application in a filter, a vibrator, or the like. With the amount x of substituting Pb by Nd in the range of the present invention, 0.02 ≤ x ≤ 0.16, a piezoelectric ceramic having a temperature coefficient of the resonance frequency within ±37 ppm/°C and a 290°C or more Curie temperature, advantageous in the application in a filter, a vibrator, or the like, can be obtained. Furthermore, as in the specimens 24, 47 and 70, if the amount y of substituting Ti by (In 1/2 Nb 1/2 ) is 0.6, which is outside the range of the present invention, the Curie temperature is lowered to 280°C or less, and thus it is not preferable for the reason mentioned above. However, if the substitution amount by (In 1/2 Nb 1/2 ) y is less than 0.15 (the specimens 2 to 5, 25 to 28, and 48 to 51), the temperature coefficient of the resonance frequency F-TC is deteriorated beyond -37 ppm/°C, and thus the amount y of substituting Ti by (In 1/2 Nb 1/2 ) needs to be in the range of the present invention, 0.15 ≤ y ≤ 0.50 in order to obtain a ceramic having both the temperature stability of the resonance frequency and the heat durability. A piezoelectric ceramic composition and a piezoelectric element using the piezoelectric ceramic composition according to the present invention are not limited to the above-mentioned embodiment, but can be modified variously in the range of the gist thereof. In particular, the piezoelectric element is not limited to the above-mentioned embodiment, but can be a vibrator, a trap element, or the like. Moreover, the vibration mode of the piezoelectric substrate can be a thickness sliding vibration mode. As apparent from the explanation provided above, according to the present invention, a piezoelectric ceramic composition having a good temperature coefficient of the resonance frequency and an excellent heat durability can be obtained. Accordingly, a piezoelectric element, such as a ceramic vibrator, a ceramic filter, or the like, having an excellent temperature stability can be realized without the risk of deteriorating the ability at the time of reflow soldering.

Claims: A piezoelectric ceramic composition containing at least Pb, Nd, In, Nb and Ti, represented by the general formula Pb 1-1.5x Nd x [(In 1/2 Nb 1/2 ) y Ti 1-y ]O 3 , wherein not less than 0.1% by weight but not more than 3.0% by weight of Mn based on MnCO 3 is contained as the sub component in the main component having a composition satisfying 0.02 ≤ x ≤ 0.16 and 0.15 ≤ y ≤ 0.50. A piezoelectric element, using the piezoelectric ceramic composition according to claim 1.

Inventors: ANDO AKIRA, HAYASHI KOICHI, HORIKAWA KATSUHIRO, YOSHIZAWA ISAMU, ANDO, AKIRA, HAYASHI, KOICHI, HORIKAWA, KATSUHIRO, YOSHIZAWA, ISAMU
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1999
Main classification: H01L41
IPC codes: H03H9, H01L41, C04B35