Piezoelectric ceramic composition

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a piezoelectric ceramic composition, and particularly to a piezoelectric ceramic composition useful as a material for piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators.
2. Background Art
Piezoelectric ceramic compositions predominantly comprising lead titanate zirconate (Pb(Ti.sub.x Zr.sub.l-x)O.sub.3) or lead titanate (PbTiO.sub.3) have been widely used for piezoelectric ceramic elements such as piezoelectric ceramic filters. In the production step for these types of piezoelectric ceramic compositions, lead oxide is generally used. However, vaporization of lead oxide causes deteriorated uniformity in characteristics of the produced elements.
In contrast, piezoelectric ceramic compositions predominantly comprising potassium sodium lithium niobate represented by a formula such as (K.sub.l-x-y Na.sub.x Li.sub.y)NbO.sub.3 do not cause the above problem since they contain no lead oxide. Some such compositions comprising potassium sodium lithium niobate have a high electromechanical coupling coefficient K.sub.p and are considered to be promising materials for producing piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators.
However, the piezoelectric ceramic compositions predominantly comprising potassium sodium lithium niobate have a relative dielectric constant lower than that of lead titanate zirconate or lead titanate. Therefore, when they are used as materials for piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators, impedance-matching with a circuit including the ceramic elements is poor and circuit design sometimes become difficult.
When a piezoelectric ceramic composition is used in a high-frequency region, the following problems arise. Since a conventional piezoelectric ceramic composition predominantly comprising lead titanate zirconate generally has a relatively high relative dielectric constant (approximately 1000-2000), impedance decreases in the high-frequency region of, for example, more than 100 MHz to cause difficulty in use thereof in such a high-frequency region.
In contrast, piezoelectric ceramic compositions predominantly comprising lead titanate (PbTiO.sub.3) generally have a relative dielectric constant of approximately 200, which is lower than that of the above piezoelectric ceramic compositions predominantly comprising lead titanate zirconate. Therefore, the compositions comprising lead titanate (PbTiO.sub.3) are known to be useful in the higher high-frequency region. However, an even lower relative dielectric constant is desired in consideration of use in a higher high-frequency region.
In addition, piezoelectric ceramic compositions predominantly comprising lead titanate zirconate or lead titanate have a resonance frequency of vibration in a thickness direction as low as approximately 2000-2500 Hz.multidot.m. Thus, when such a piezoelectric ceramic composition is processed into a thin slice so as to form a vibrator, the vibrator must be used in a limited frequency band.
In contrast, some of the piezoelectric ceramic compositions predominantly comprising potassium sodium lithium niobate represented by a formula such as (K.sub.l-x-y Na.sub.x Li.sub.y)NbO.sub.3 have a resonance frequency of vibration in a thickness direction as low as approximately 3000-3500 Hz.multidot.m and a relative dielectric constant of approximately 100, which is lower than that of lead titanate. Therefore, some of the compositions are known to be used as a material which has characteristics more advantageous than those of lead titanate zirconate or lead titanate in consideration of use thereof in the high-frequency region.
However, the piezoelectric ceramic compositions predominantly comprising potassium sodium lithium niobate have a large temperature-dependent factor of resonance frequency of vibration in a thickness direction as high as approximately 150-300 ppm. This factor is referred to as fr-TC, and represents an important characteristic of a material for piezoelectric ceramic filters and piezoelectric ceramic oscillators. Therefore, the piezoelectric ceramic compositions have not yet been used widely in practice, as compared with lead titanate zirconate, lead titanate, etc.
The above-described temperature-dependent factor of resonance frequency of vibration in a thickness direction represented by fr-TC is calculated from the following equation:
fr-TC=(fr.sub.max -fr.sub.min)/(fr.sub.20 .multidot.100)
wherein fr.sub.max represents the maximum resonance frequency of vibration in a thickness direction within a temperature range of -20.degree. C. to +80.degree. C.; fr.sub.min represents a minimum resonance frequency of vibration in the thickness direction within a temperature range of -20.degree. C. to +80.degree. C.; and fr.sub.20 represents a resonance frequency of vibration in the thickness direction at 20.degree. C.
SUMMARY OF THE INVENTION
The present invention has been achieved in an attempt to solve the above-mentioned problems with piezoelectric ceramic compositions predominantly comprising potassium sodium lithium niobate.
Accordingly, an object of the present invention is to provide a lead-free piezoelectric ceramic composition which has an enhanced relative dielectric constant of 1000 or more and an electromechanical coupling coefficient represented by K.sub.p of a practically sufficient value, e.g., 25% or more.
Another object of the present invention is to provide a piezoelectric ceramic composition in which the temperature-dependent factor of resonance frequency represented by fr-TC is favorable, i.e., 100 ppm or less, and the relative dielectric constant is 180 or less, and which composition is suitably used in the high-frequency region and under conditions that the temperature-dependent factor of resonance frequency of vibration in a thickness direction is 3000 Hz.multidot.m or more.
Broadly, the present invention provides a piezoelectric ceramic composition represented by the formula:
(1-n)(K.sub.l-x-y Na.sub.x Li.sub.y).sub.m (Nb.sub.l-z Ta.sub.z)O.sub.3 -nM1M2O.sub.3
wherein M1 represents a divalent metal element; M2 represents a tetravalent metal element; and x, y, z, m, and n satisfy the following conditions: 0.9.ltoreq.x; y.ltoreq.0.3; x+y.ltoreq.0.75; 0.ltoreq.z.ltoreq.0.3; 0.98.ltoreq.m.ltoreq.1.0; and 0<n<0.1.
In a first aspect of the present invention, there is provided a piezoelectric ceramic composition which predominantly comprises a composition represented by the following formula:
(l-n)(K.sub.l-x-y Na.sub.x Li.sub.y).sub.m (Nb.sub.l-z Ta.sub.z)O.sub.3 -nM1M2O.sub.3
wherein M1 represents a divalent metal element; M2 represents a tetravalent metal element; and x, y, z, m, and n satisfy the following conditions: 0.1.ltoreq.x; y.ltoreq.0.3; x+y<0.75; 0.ltoreq.z.ltoreq.0.3; 0.98.ltoreq.m.ltoreq.1.0; and 0<n<0.1.
Preferably, M1 is at least one element selected from the group consisting of Mg, Ca, Sr and Ba, and M2 is at least one element selected from the group consisting of Ti, Zr, Sn and Hf.
According to the first aspect of the present invention, there can be obtained a piezoelectric ceramic composition having excellent characteristics, e.g., a relative dielectric constant of 1000 or more, an electromechanical coupling coefficient represented by K.sub.p of 25% or more and a Curie point of more than 200.degree. C.
In a second aspect of the present invention, there is provided a piezoelectric ceramic composition which predominantly comprises a composition represented by the following formula:
(l-n)(K.sub.l-x-y Na.sub.x Li.sub.y).sub.m (Nb.sub.l-z Ta.sub.z)O.sub.3 -nM1M2O.sub.3
wherein M1 represents a divalent metal element; M2 represents a tetravalent metal element; and x, y, z, m, and n satisfy the following conditions: x.ltoreq.0.9; 0.02.ltoreq.y.ltoreq.0.3; 0.75.ltoreq.x+y; 0.ltoreq.z.ltoreq.0.3; 0.98.ltoreq.m.ltoreq.1.0; and 0<n.ltoreq.0.05.
Preferably, M1 is at least one element selected from the group consisting of Mg, Ca, Sr and Ba, and M2 is at least one element selected from the group consisting of Ti, Zr, Sn and Hf.
According to the second aspect of the present invention, there can be obtained a piezoelectric ceramic composition having excellent characteristics, e.g., a temperature-dependent factor of resonance frequency represented by fr-TC of 100 ppm or less and a Curie point of more than 200.degree. C. and which composition is suitably used in the high-frequency region and under the conditions that the relative dielectric constant is 180 or less and the temperature-dependent factor of resonance frequency of vibration in a thickness direction is 3000 Hz.multidot.m or more.
By use of the piezoelectric ceramic composition of the first or the second aspect of the present invention, piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators are advantageously produced so as to meet the desired characteristics of the elements to be produced.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
As described above, the piezoelectric ceramic composition according to the present invention predominantly comprises a composition represented by the following formula.
(l-n)(K.sub.l-x-y Na.sub.x Li.sub.y).sub.m (Nb.sub.l-z Ta.sub.z)O.sub.3 -nM1M2O.sub.3
With reference to the first aspect of the present invention, the reasons why the parameters are limited to the given ranges will next be described.
The x and y are limited such that 0.1<x and y.ltoreq.0.3 because when x and y fall outside the ranges, sintered products are unsatisfactory. The x+y is limited such that x+y<0.75 because when x+y is 0.75 or more, the electromechanical coupling coefficient represented by K.sub.p decreases to less than 25% to thereby result in difficulty in application of the composition to a material for piezoelectric ceramic filters, piezoelectric ceramic oscillators, etc.
The z is limited such that 0.ltoreq.z.ltoreq.0.3. When z falls outside the range, the Curie point decreases to 200.degree. C. or less to cause a problem in variation of characteristics with respect to temperature change of elements formed of the piezoelectric ceramic composition according to the present invention.
The m is limited such that 0.98.ltoreq.m.ltoreq.1.0. When m falls outside the range, polarization treatment of a fired piezoelectric ceramic composition is difficult.
The n is limited such that 0<n<0.1. When n is 0.1 or more, the electromechanical coupling coefficient represented by K.sub.p decreases to less than 25% to thereby result in difficulty in application of the composition to a material for piezoelectric ceramic filters, piezoelectric ceramic oscillators, etc.
With reference to the second aspect of the present invention, the reasons why the parameters are limited to the given ranges will next be described.
The x and y are limited such that x.ltoreq.0.9 and 0.02.ltoreq.y.ltoreq.0.3 because when x and y fall outside the ranges, sintered products are unsatisfactory. The value x+y is limited such that 0.75.ltoreq.x+y because when less than 0.75, the relative dielectric constant is in excess of 180, to thereby lose advantages in application of the composition in the high-frequency region.
The z is limited such that 0.ltoreq.z.ltoreq.0.3. When z falls outside the range, the Curie point decreases to 200.degree. C. or less to cause a problem in variation of characteristics with respect to temperature change of elements formed of the piezoelectric ceramic composition according to the present invention.
The m is limited such that 0.98.ltoreq.m.ltoreq.1.0. When m falls outside the range, polarization treatment of a fired piezoelectric ceramic composition is difficult.
The n is limited such that 0<n.ltoreq.0.05. When n is in excess of 0.05, the Curie point decreases to 200.degree. C. or less to cause a problem in variation of characteristics with respect to temperature change of elements formed of the piezoelectric ceramic composition according to the present invention.

EXAMPLES
The present invention will next be described in detail by way of examples, which should not be construed as limiting the invention thereto.
Example 1
K.sub.2 CO.sub.3, Na.sub.2 CO.sub.3, Li.sub.2 CO.sub.3, Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, CaCO.sub.3, SrCO.sub.3, BaCO.sub.3, TiO.sub.2, ZrO.sub.2 and SnO.sub.2 were provided as starting raw materials and were weighed so as to form compositions of the formula (l-n)(K.sub.l-x-y Na.sub.x Li.sub.y).sub.m (Nb.sub.l-z Ta.sub.z)O.sub.3 -nM1M2O.sub.3 shown in Table 1. For each sample, the starting materials were wet-mixed in alcohol for about four hours by use of a ball mill, and the resultant mixture was dried and then calcined at 700-900.degree. C. Subsequently, the dried mixture was roughly crushed, wet-milled with an appropriate amount of an organic binder for four hours by use of a ball mill, and passed through a 40-mesh sieve to thereby adjust the particle size of the milled powder.
Subsequently, the particle-size-adjusted powder was molded at 1000 kg/cm.sup.2 into a disk having a diameter of 12 mm and a thickness of 1.2 mm, and the disk was fired at 1050.degree. C.-1300.degree. C. through a customary method for firing to thereby form a ceramic disk. Subsequently, silver electrodes were formed on both sides of the ceramic disk by applying and burning a silver paste through customary methods. The disk was subjected to polarization treatment by the application of a DC voltage of 2-10 kV/mm for 10-30 minutes in a 50.degree. C.-150.degree. C. insulating oil to thereby obtain a piezoelectric ceramic disk serving as a sample.
Relative dielectric constant, electromechanical coupling coefficient represented by K.sub.p and Curie point were measured for the obtained samples. The results are shown in Table 1.
TABLE 1__________________________________________________________________________ Relative ElectromechanicalSample x y z m n Dielectric coupling Curie PointNo. M1 M2 mol mol mol mol mol Constant coefficient K.sub.P (.degree. C.)__________________________________________________________________________*1 Ca Ti 0.7 0.1 0 1 0.05 850 22.0 430*2 -- -- 0.6 0.1 0 1 0 580 36.5 400 3 Ca Ti 0.6 0.1 0 1 0.05 1010 31.0 370 4 Ca Ti 0.6 0.1 0 1 0.09 1280 29.5 310*5 Ca Ti 0.6 0.1 0 1 0.1 1350 23.5 250*6 -- -- 0.4 0.1 0 1 0 650 35.5 370 7 Ca Ti 0.4 0.1 0 1 0.05 1110 30.0 290 8 Ca Ti 0.4 0.1 0 1 0.09 1310 28.5 235*9 Ca Ti 0.4 0.1 0 1 0.1 1420 24.5 215*10 -- -- 0.1 0.1 0 1 0 350 28.0 40511 Ca Ti 0.1 0.1 0 1 0.05 1005 27.0 36512 Ca Ti 0.1 0.1 0 1 0.09 1220 25.5 300*13 Ca Ti 0.1 0.1 0 1 0.1 1240 22.0 260*14 Ca Ti 0.05 0.1 0 1 0.05 Poor sintering*15 Ca Ti 0.4 0.4 0 1 0.05 Poor sintering*16 -- -- 0.4 0.3 0 1 0 470 27.5 38017 Ca Ti 0.4 0.3 0 1 0.05 1100 26.0 30018 Ca Ti 0.4 0.3 0 1 0.09 1210 25.0 225*19 Ca Ti 0.4 0.3 0 1 0.1 1270 21.5 205*20 -- -- 0.4 0 0 1 0 420 37.0 37521 Ca Ti 0.4 0 0 1 0.05 1010 32.0 29522 Ca Ti 0.4 0 0 1 0.09 1240 29.5 265*23 Ca Ti 0.4 0 0 1 0.1 1360 24.5 240*24 -- -- 0.4 0 0.1 1 0 505 39.0 36525 Ca Ti 0.4 0 0.1 1 0.05 1150 34.5 28026 Ca Ti 0.4 0 0.1 1 0.09 1270 27.5 240*27 Ca Ti 0.4 0 0.1 1 0.1 1370 24.5 230*28 -- -- 0.4 0 0.3 1 0 570 36.0 31529 Ca Ti 0.4 0 0.3 1 0.05 1190 30.5 23530 Ca Ti 0.4 0 0.3 1 0.09 1320 26.0 215*31 Ca Ti 0.4 0 0.3 1 0.1 1420 23.0 200*32 Ca Ti 0.4 0 0.4 1 0.05 1500 34.0 160*33 -- -- 0.4 0 0 0.98 0 425 40.5 38034 Ca Ti 0.4 0 0 0.98 0.05 1020 38.0 29035 Ca Ti 0.4 0 0 0.98 0.09 1210 30.5 265*36 Ca Ti 0.4 0 0 0.98 0.1 1280 24.5 240*37 Ca Ti 0.4 0 0 0.97 0.05 Not polarized38 Ba Ti 0.4 0 0 1 0.05 1100 31.5 28039 Ba Ti 0.4 0 0 1 0.09 1240 27.5 250*40 Ba Ti 0.4 0 0 1 0.1 1400 23.0 23541 Ca.sub.1/2 Sr.sub.1/2 Ti 0.4 0 0 1 0.05 1005 32.0 32042 Ca.sub.1/2 Sr.sub.1/2 Ti 0.4 0 0 1 0.09 1070 28.0 280*43 Ca.sub.1/2 Sr.sub.1/2 Ti 0.4 0 0 1 0.1 1105 24.0 25544 Ca Zr 0.4 0 0 1 0.05 1045 33.5 30545 Ca Zr 0.4 0 0 1 0.09 1125 28.0 265*46 Ca Zr 0.4 0 0 1 0.1 1220 24.5 25047 Ca Ti.sub.1/2 Sn.sub.1/2 0.4 0 0 1 0.05 1200 30.0 28048 Ca Ti.sub.1/2 Sn.sub.1/2 0.4 0 0 1 0.09 1410 26.0 235*49 Ca Ti.sub.1/2 Sn.sub.1/2 0.4 0 0 1 0.1 1500 22.5 200__________________________________________________________________________
In Table 1, samples marked with * fall outside the scope of the present invention.
Samples in Table 1 satisfying all the following conditions: 0.1.ltoreq.x; y.ltoreq.0.3; x+y<0.75; 0.ltoreq.z.ltoreq.0.3; 0.98.ltoreq.m.ltoreq.1.0; and 0<n<0.1 exhibit excellent characteristics. Briefly, all samples according to the present invention (those not marked with *) have a relative dielectric constant of 1000 or more, an electromechanical coupling coefficient represented by K.sub.p of 25% or more and a Curie point of more than 200.degree. C.
In contrast, Sample Nos. 14 and 15, which fail to satisfy either the condition 0.1.ltoreq.x or the condition y.ltoreq.0.3, exhibited poor sinterability.
Sample No. 1, which satisfies the condition 0.1.ltoreq.x or and? y.ltoreq.0.3 and does not satisfy the condition x+y<0.75, has an electromechanical coupling coefficient represented by K.sub.p of 22.0%. Sample No. 1 also has a relative dielectric constant of 850. As shown by the data, Sample No. 1 does not attain the relative dielectric constant of 1000 or more and electromechanical coupling coefficient represented by K.sub.p of 25% or more.
Sample No. 32, which does not satisfy the condition 0.ltoreq.z.ltoreq.0.3, has a Curie point of 160.degree. C. and thus does not attain a Curie point of more than 200.degree. C.
Sample No. 37, which does not satisfy the condition 0.98.ltoreq.m.ltoreq.1.0, does not attain desirable polarization.
Among the samples which do not satisfy the condition 0<n<0.1, Sample Nos. 5, 9, 13, 19, 23, 27, 31, 36, 40, 43, 46 and 49 having an n of 0.1 or more have an electromechanical coupling coefficient represented by K.sub.p of lower than 25% and Sample Nos. 2, 6, 10, 16, 20, 24, 28 and 33 having an n of 0 do not attain a relative dielectric constant of 1000 or more.
In Example 1, at least one species selected from the group consisting of Ca, Ba and Sr was used as M1; and at least one species selected from the group consisting of Ti, Zr and Sn was used as M2. However, the inventors confirmed that equivalent effects can be realized when Mg is used as M1 and Hf is used as M2. Other divalent metals and tetravalent metals may also be used as M1 and M2, respectively.
As demonstrated by this Example, the first aspect of the present invention provides a piezoelectric ceramic composition exhibiting excellent characteristics; i.e., an enhanced relative dielectric constant of 1000 or more, an electromechanical coupling coefficient represented by K.sub.p of 25% or more, and a Curie point of higher than 200.degree. C. Therefore, by use of the piezoelectric ceramic composition according to the first aspect of the present invention, piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators are advantageously produced.
Example 2
K.sub.2 CO.sub.3, Na.sub.2 CO.sub.3, Li.sub.2 CO.sub.3, Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, CaCO.sub.3, SrCO.sub.3, BaCO.sub.3, TiO.sub.2, ZrO.sub.2 and SnO.sub.2 were provided as starting raw materials and were weighed so as to form compositions of the formula (ln)(K.sub.l-x-y Na.sub.x Li.sub.y).sub.m (Nb.sub.l-z Ta.sub.z)O.sub.3 -nM1M2O.sub.3 shown in Tables 2 and 3. For each sample, the starting materials were wet-mixed in alcohol for about four hours by use of a ball mill, and the resultant mixture was dried and then calcined at 700-900.degree. C. Subsequently, the dried mixture was roughly crushed, wet-milled with an appropriate amount of an organic binder for four hours by use of a ball mill and passed through a 40-mesh sieve to thereby adjust the particle size of the milled powder.
Subsequently, the particle-size-adjusted powder was molded at 1000 kg/cm.sup.2 into a disk having a diameter of 12 mm and a thickness of 1.2 mm, and the disk was fired at 1050.degree. C.-1300.degree. C. through a customary method for firing to thereby form a ceramic disk. Subsequently, silver electrodes were formed on both sides of the ceramic disk by applying and burning a silver paste through customary methods. The disk was subjected to polarization treatment by the application of a DC voltage of 2-10 kV/mm for 10-30 minutes in a 50.degree. C.-150.degree. C. insulating oil, to thereby obtain a piezoelectric ceramic disk serving as a sample.
TABLE 2______________________________________Sample x y z m nNo. M1 M2 mol mol mol mol mol______________________________________*101 Ca Ti 0.95 0.05 0 1 0.01*102 -- -- 0.9 0.1 0 1 0103 Ca Ti 0.9 0.1 0 1 0.01104 Ca Ti 0.9 0.1 0 1 0.05*105 Ca Ti 0.9 0.1 0 1 0.06*106 -- -- 0.85 0.15 0 1 0107 Ca Ti 0.85 0.15 0 1 0.01108 Ca Ti 0.85 0.15 0 1 0.02109 Ca Ti 0.85 0.15 0 1 0.05*110 Ca Ti 0.85 0.15 0 1 0.06*111 -- -- 0.8 0.2 0 1 0112 Ca Ti 0.8 0.2 0 1 0.01113 Ca Ti 0.8 0.2 0 1 0.05*114 Ca Ti 0.8 0.2 0 1 0.06*115 -- -- 0.7 0.3 0 1 0116 Ca Ti 0.7 0.3 0 1 0.01117 Ca Ti 0.7 0.3 0 1 0.05*118 Ca Ti 0.7 0.3 0 1 0.06*119 Ca Ti 0.9 0 0 1 0.01*120 -- -- 0.88 0.02 0 1 0121 Ca Ti 0.88 0.02 0 1 0.01122 Ca Ti 0.88 0.02 0 1 0.05*123 Ca Ti 0.88 0.02 0 1 0.06*124 -- -- 0.75 0.15 0 1 0125 Ca Ti 0.75 0.15 0 1 0.01126 Ca Ti 0.75 0.15 0 1 0.05*127 Ca Ti 0.75 0.15 0 1 0.06*128 -- -- 0.6 0.3 0 1 0129 Ca Ti 0.6 0.3 0 1 0.01130 Ca Ti 0.6 0.3 0 1 0.05*131 Ca Ti 0.6 0.3 0 1 0.06*132 Ca Ti 0.5 0.4 0 1 0.01*133 -- -- 0.73 0.02 0 1 0134 Ca Ti 0.73 0.02 0 1 0.01135 Ca Ti 0.73 0.02 0 1 0.05*136 Ca Ti 0.73 0.02 0 1 0.06*137 -- -- 0.6 0.15 0 1 0______________________________________
TABLE 3______________________________________Sample x y z m nNo. M1 M2 mol mol mol mol mol______________________________________138 Ca Ti 0.6 0.15 0 1 0.01139 Ca Ti 0.6 0.15 0 1 0.05*140 Ca Ti 0.6 0.15 0 1 0.06*141 -- -- 0.45 0.3 0 1 0142 Ca Ti 0.45 0.3 0 1 0.01143 Ca Ti 0.45 0.3 0 1 0.05*144 Ca Ti 0.45 0.3 0 1 0.06*145 Ca Ti 0.4 0.3 0 1 0.01*146 -- -- 0.88 0.02 0.1 1 0147 Ca Ti 0.88 0.02 0.1 1 0.01148 Ca Ti 0.88 0.02 0.1 1 0.05*149 Ca Ti 0.88 0.02 0.1 1 0.06*150 -- -- 0.88 0.02 0.3 1 0151 Ca Ti 0.88 0.02 0.3 1 0.01152 Ca Ti 0.88 0.02 0.3 1 0.05*153 Ca Ti 0.88 0.02 0.3 1 0.06*154 Ca Ti 0.88 0.02 0.4 1 0.01*155 -- -- 0.88 0.02 0 0.99 0156 Ca Ti 0.88 0.02 0 0.99 0.01157 Ca Ti 0.88 0.02 0 0.99 0.05*158 Ca Ti 0.88 0.02 0 0.99 0.06*159 -- -- 0.88 0.02 0 0.98 0160 Ca Ti 0.88 0.02 0 0.98 0.01161 Ca Ti 0.88 0.02 0 0.98 0.05*162 Ca Ti 0.88 0.02 0 0.98 0.06*163 Ca Ti 0.88 0.02 0 0.97 0.01164 Ba Ti 0.88 0.02 0 1 0.01165 Ba Ti 0.88 0.02 0 1 0.05*166 Ba Ti 0.88 0.02 0 1 0.06167 Ca.sub.1/2 Sr.sub.1/2 Ti 0.88 0.02 0 1 0.01168 Ca.sub.1/2 Sr.sub.1/2 Ti 0.88 0.02 0 1 0.05*169 Ca.sub.1/2 Sr.sub.1/2 Ti 0.88 0.02 0 1 0.06170 Ca Zr 0.88 0.02 0 1 0.01171 Ca Zr 0.88 0.02 0 1 0.05*172 Ca Zr 0.88 0.02 0 1 0.06173 Ca Ti.sub.1/2 Sn.sub.1/2 0.88 0.02 0 1 0.01174 Ca Ti.sub.1/2 Sn.sub.1/2 0.88 0.02 0 1 0.05*175 Ca Ti.sub.1/2 Sn.sub.1/2 0.88 0.02 0 1 0.06______________________________________
Relative dielectric constant, electromechanical coupling coefficient in vibration in a thickness direction represented by K.sub.t, resonance frequency constant of vibration in a thickness direction represented by N, temperature-dependent factor of resonance frequency of vibration in a thickness direction represented by fr-TC and Curie point were measured for the obtained samples shown in Table 2 and 3. The results are shown in Tables 4 and 5.
TABLE 4______________________________________ Temperature- Electro- Resonance Dependent mechanical Frequency Factor of Relative Coupling Constant of Resonance CurieSample Dielectric Coefficient Vibration Frequency PointNo. Constant (%) (Hz .multidot. m) (ppm) (.degree. C.)______________________________________*101 Poor sintering*102 105 42 3460 170 420103 115 40 3570 95 380104 145 38 3640 85 220*105 160 24 3820 85 180*106 90 48 3620 175 425107 95 43 3710 90 410108 100 42 3740 90 400109 120 40 3770 90 270*110 140 29 3850 90 190*111 90 45 3640 200 435112 95 41 3710 95 420113 115 35 3700 90 285*114 125 22 3740 85 195*115 85 35 3580 250 440116 95 32 3600 100 415117 110 25 3600 95 290*118 115 18 3610 100 195*119 Poor sintering*120 110 48 3420 220 400121 125 44 3425 90 380122 145 37 3420 85 265*123 160 30 3440 85 190*124 105 40 3405 260 410125 105 32 3390 95 395126 125 29 3390 85 285*127 125 26 3405 90 190*128 105 38 3400 255 410129 110 33 3400 100 390130 120 26 3385 95 290*131 120 20 3370 95 185*132 Poor sintering*133 165 38 3200 310 400134 165 29 3220 100 350135 175 26 3240 95 225*136 175 18 3230 100 155*137 150 40 3235 260 415______________________________________
TABLE 5______________________________________ Temperature- Electro- Resonance Dependent mechanical Frequency Factor of Relative Coupling Constant of Resonance CurieSample Dielectric Coefficient Vibration Frequency PointNo. Constant (%) (Hz .multidot. m) (ppm) (.degree. C.)______________________________________138 155 29 3240 90 385139 170 24 3260 85 280*140 170 20 3260 85 185*141 110 37 3300 195 425142 120 31 3305 100 395143 125 26 3415 100 305*144 125 20 3385 100 195*145 200 35 3085 100 400*146 130 48 3220 260 350147 135 40 3205 100 325148 145 35 3215 95 205*149 170 32 3260 100 155*150 160 47 3205 245 270151 170 39 3185 95 245152 175 32 3170 95 205*153 175 29 3170 95 160*154 180 35 3015 100 165*155 110 49 3420 220 395156 125 46 3425 90 380157 145 40 3415 85 265*158 160 36 3445 85 185*159 110 47 3400 220 390160 125 43 3415 90 375161 140 37 3405 85 255*162 155 29 3430 85 180*163 Not polarized164 125 40 3325 95 380165 140 34 3320 95 245*166 150 28 3315 90 180167 120 40 3475 95 380168 135 32 3430 85 255*169 135 27 3420 85 185170 125 43 3440 90 380171 145 37 3455 85 265*172 155 27 3470 85 180173 135 47 3355 95 355174 165 40 3320 95 225*175 170 32 3305 95 165______________________________________
In Tables 2 to 5, samples marked with * fall outside the scope of the present invention.
Those samples in Tables 2 and 3 satisfying all the following conditions: x.ltoreq.0.9; 0.02.ltoreq.y.ltoreq.0.3; 0.75.ltoreq.x+y; 0.ltoreq.z.ltoreq.0.3; 0.98.ltoreq.m.ltoreq.1.0; and 0<n.ltoreq.0.05 exhibit excellent characteristics. Briefly, as shown in Tables 4 and 5, all samples according to the present invention (those not marked with *) have a relative dielectric constant of 180 or less, a resonance frequency constant of vibration in a thickness direction of 3000 Hz.multidot.m or more, a temperature-dependent factor of resonance frequency of 100 ppm or less and a Curie point of more than 200.degree. C.
In contrast, Sample Nos. 101, 119 and 132, which fail to satisfy either the condition x.ltoreq.0.9 or the condition 0.02.ltoreq.y.ltoreq.0.3 exhibited poor sinterability.
Sample No. 145, which does not satisfy the condition 0.75.ltoreq.x+y, has a relative dielectric constant of 200 and thus does not attain a relative dielectric constant of 180 or less.
Sample No. 154, which does not satisfy the condition 0.ltoreq.z.ltoreq.0.3, has a Curie point of 165.degree. C. and thus does not attain a Curie point of more than 200.degree. C.
Sample No. 163, which does not satisfy the condition 0.98.ltoreq.m.ltoreq.1.0, does not attain desirable polarization.
Among the samples which do not satisfy the condition 0<n.ltoreq.0.05, Sample Nos. 105, 110, 114, 118, 123, 127, 131, 136, 140, 144, 149, 153, 158, 162, 166, 169, 172 and 175 having an n of greater than 0.05 have a Curie point of 200.degree. C. or less, and Sample Nos. 102, 106, 111, 115, 120, 124, 128, 133, 137, 141, 146, 150, 155 and 159 having an n of 0 have a temperature-dependent factor of resonance frequency in great excess of 100 ppm.
In Example 2, at least one species selected from the group consisting of Ca, Ba and Sr was used as M1; and at least one species selected from the group consisting of Ti, Zr and Sn was used as M2. However, the inventors confirmed that equivalent effects can be realized when Mg and/or Pb are used as M1 and Hf is used as M2. Other divalent metals and tetravalent metals may also be used as M1 and M2, respectively.
As demonstrated by this Example, the second aspect of the present invention provides a piezoelectric ceramic composition exhibiting excellent characteristics; i.e., a relative dielectric constant of 180 or less and a temperature-dependent factor of resonance frequency of vibration in a thickness direction of 3000 Hz.multidot.m or more, proving that the composition can be advantageously used in a high frequency region. Moreover, the composition has a temperature-dependent factor of resonance frequency represented by fr-TC of 100 ppm or less and a Curie point of higher than 200.degree. C. Therefore, by use of the piezoelectric ceramic composition according to the second aspect of the present invention, piezoelectric ceramic elements such as piezoelectric ceramic filters and piezoelectric ceramic oscillators are advantageously produced.
Although the present invention has been described above with reference to nonlimiting examples, those skilled in the art will recognize that many variations on the piezoelectric ceramic composition of the present invention are possible. Such variations are intended to be within the scope of the present invention.

Number	Date	Country	Kind
10-035713	Feb 1998	JPX
10-035715	Feb 1998	JPX

Piezoelectric ceramic composition

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