Abstract:
Provided is a piezoelectric ceramic composition containing a lead titanate which has excellent temperature stability of the resonance frequency, and is suitable for 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 about 0.1% by weight or more than about 3.0% by weight of Mn based on MnCO 3  as the subcomponent 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 
     Conventional piezoelectric ceramic composition containing a lead titanate (PbTiO 3 ) are known. Since a piezoelectric ceramic composition containing a lead titanate has a low dielectric constant and small particle size, it is suitable for the use in the high frequency range. Moreover, it has excellent characteristics such as ability in restraining sub-resonance due to large piezoelectric anisotropy, durability in use at a high temperature due to a high Curie point, and the like. Therefore, use of a piezoelectric ceramic containing lead titanate is indicated in the field of filters, vibrators, or the like, intended to be used in a high frequency range. However, the 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 these problems, for example, a piezoelectric ceramic composition containing a lead titanate obtained by partially substituting the Pb of PbTiO 3  by La and adding a Mn compound such as MnCO 3  or the like has been used. Such 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 temperature. Therefore, it has been difficult to use a ceramic containing lead titanate in a filter or a vibrator, which are 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, suitability for 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 about 0.1% by weight but not more than about 3.0% by weight of Mn based on MnCO 3  is contained as a subcomponent in a 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 (substituting Nd by Pd) 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&lt;0.02, and the Curie temperature is drastically deteriorated so as not to be durable at high temperature if 0.16&lt;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&lt;0.15, and the Curie temperature is drastically deteriorated so as not to be durable at high temperature if 0.50&lt;y. The amount of Mn as the subcomponent is preferably not less than about 0.1% by weight and not more than about 3.0% by weight as 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 about 0.1% by weight, and 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 about 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 
     An embodiment of a piezoelectric ceramic composition and a piezoelectric element using the piezoelectric ceramic composition according to the present invention will hereinafter 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 conductive adhesive paste 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 parts 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  and MnCO 3  were used. Other oxides of Pb, Nd, In, Nb, Ti, Mn, or a compound convertible to an oxide can also be used. 
     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. 
     
                                           TABLE 1__________________________________________________________________________SpecimenNd substitution       In.sub.1/2 Nb.sub.1/2 substitution                 MnCO.sub.3 content                        k.sub.t                              T.sub.c                                 F-TCnumberx amount       y amount  (% by weight)                        (%)                           Q.sub.m                              (° C.)                                 (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                                 -627    0.02   0.15      0.1    38 540                              380                                 -348    0.10   0.15      0.1    40 550                              360                                 -99    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                                 -5912   0.02   0.20      0.1    39 550                              370                                 -3313   0.10   0.20      0.1    41 540                              350                                 514   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                                 -4417   0.02   0.35      0.1    42 590                              350                                 -3018   0.10   0.35      0.1    41 540                              320                                 1019   0.16   0.35      0.1    44 550                              290                                 10*20  0.18   0.35      0.1    44 520                              260                                 4021   0.02   0.50      0.1    42 500                              330                                 -1022   0.10   0.50      0.1    43 480                              290                                 1123   0.16   0.50      0.1    44 510                              290                                 14*24  0.10   0.60      0.1    45 450                              280                                 45__________________________________________________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________SpecimenNd substitution       In.sub.1/2 Nb.sub.1/2 substitution                 MnCO.sub.3 content                        k.sub.t                              T.sub.c                                 F-TCnumberx amount       y amount  (% by weight)                        (%)                           Q.sub.m                              (° C.)                                 (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                                 -6630   0.02   0.15      3.0    40 2010                              380                                 -3331   0.10   0.15      3.0    41 1910                              360                                 -1232   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                                 -6035   0.02   0.20      1.0    40 2030                              370                                 -3036   0.10   0.20      1.0    42 1990                              350                                 237   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                                 -5040   0.02   0.35      3.0    41 1990                              350                                 -2241   0.10   0.35      3.0    43 2000                              320                                 842   0.16   0.35      3.0    43 1920                              290                                 13*43  0.18   0.35      3.0    44 1940                              260                                 2044   0.02   0.50      1.0    41 1940                              330                                 -2145   0.10   0.50      1.0    43 1960                              290                                 946   0.16   0.50      1.0    45 1960                              290                                 14*47  0.10   0.60      1.0    44 1900                              260                                 8__________________________________________________________________________ 
    
     
                                           TABLE 3__________________________________________________________________________SpecimenNd substitution       In.sub.1/2 Nb.sub.1/2 substitution                 MnCO.sub.3 content                        k.sub.t                              T.sub.c                                 F-TCnumberx amount       y amount  (% by weight)                        (%)                           Q.sub.m                              (° C.)                                 (ppm/° C.)__________________________________________________________________________*48  0.10   0.00      3.0    37 2110                              380                                 -5249   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                                 -6653   0.02   0.15      3.0    40 2020                              380                                 -3654   0.10   0.15      3.0    41 2060                              360                                 -1055   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                                 -6258   0.02   0.20      3.0    40 1980                              370                                 -3559   0.10   0.20      3.0    42 1950                              350                                 760   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                                 -5063   0.02   0.35      3.0    40 2080                              350                                 -3564   0.10   0.35      3.0    41 2110                              370                                 1065   0.16   0.35      3.0    41 2000                              290                                 11*66  0.18   0.35      3.0    40 2050                              260                                 1667   0.02   0.50      3.0    41 2050                              330                                 -2568   0.10   0.50      3.0    45 2100                              290                                 1269   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 subcomponent MnCO 3 , which is outside the range of the present invention, has a mechanical quality coefficient Qm of 200 or less, it is not suitable for the application in a filter, a vibrator or the like. Moreover, if the subcomponent MnCO 3  content is increased to 5% by weight, the insulating property of the sintered compact is deteriorated so that the polarization cannot be achieved. Therefore, in the present invention, the content of the subcomponent MnCO 3  is defined to be not less than about 0.1% by weight and not more than about 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. When the Curie temperature is 280° C. or less, the piezoelectric property of the ceramic is drastically deteriorated by 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 (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., and 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 (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 temperature stability of the resonance frequency and 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 within the gist hereof. 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, a piezoelectric ceramic composition having a good temperature coefficient of the resonance frequency and an excellent heat durability can be obtained according to the present invention. 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 properties at the time of reflow soldering.