Piezoelectric porcelain

Abstract: Piezoelectric porcelain is a lead-containing composite oxide which is expressed in a general formula aPb x (Cr y Nb 1-y )O₃-bPb x TiO₃-cPb x ZrO₃, with a, b and c being in the following ranges respectively: 1.0 ≦ a ≦ 12.0 40.5 ≦ b ≦ 49.0 39.0 ≦ c ≦ 58.5 where a, b and c are in units of mole % and a + b + c = 100 , and x and y being in the following ranges respectively: 0.95 ≦ x ≦ 1.01 2/24 ≦ y ≦ 11/24

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to piezoelectric porcelain which is applied to a piezoelectric element such as a ceramic filter, a speaker, a microphone, a buzzer or a sensor. Description of the Background Art In general, piezoelectric porcelain which is applied to a ceramic filter or the like is mainly composed of lead titanate zirconate (Pb(Ti x Zr 1-x )O 3 ). Slight amounts of various additives are added to such piezoelectric porcelain, in order to improve its piezoelectricity. A piezoelectric material which is basically composed of Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 -PbZrO 3 , known as one of lead titanate zirconate materials, is generally prepared by mixing oxide raw materials such as lead oxide, zirconium oxide, titanium oxide, magnesium oxide and niobium pentoxide with each other to attain a prescribed stoichiometric composition, mixing and dispersing the same in a ball mill or the like, thereafter calcining the mixture at a prescribed temperature, crushing the mixture and mixing the same with a binder, molding the mixture into a prescribed shape, firing the same at a high temperature of at least 1200°C to make sintering reaction, and polarizing the sintered body. When such piezoelectric porcelain is applied to an electromechanical transducer element such as a speaker or a microphone requiring a high output voltage and a flat frequency response, it is desirable that the material itself has a large electromechanical coupling factor and a high dielectric constant, in order to increase the electrostatic capacitance of the element. Japanese Patent Publication No. 44-17103 (1969) describes Pb(Mg 1/3 Nb 2/3 )O 3 -PbTiO 3 -PbZrO 3 porcelain as piezoelectric porcelain which attains the aforementioned object. However, the electromechanical coupling factor of the piezoelectric porcelain described in this gazette is too small to completely solve the problem. When the width between attenuation poles depends on the electromechanical coupling factor in a filter which is prepared from piezoelectric porcelain for serving as an electromechanical transducer element, the material desirably has a large electromechanical coupling factor and a small mechanical quality factor. However, the piezoelectric porcelain described in Japanese Patent Publication No. 44-17103 is insufficient in electromechanical coupling factor and mechanical quality factor. US-A-39 56 150 discloses piezoelectric porcelain compositions of the general formula Pb([B] A Nb 1-A )O 3 -PbTiO 3 -PbZrO 3 , where B is selected from a group of metals which does not include chromium. SUMMARY OF THE INVENTION An object of the present invention is to provide piezoelectric porcelain having a large electromechanical coupling factor, a small mechanical quality factor and a high dielectric constant, which can broaden the band of a filter and is applicable to a speaker, a microphone, a buzzer or a sensor. The piezoelectric porcelain according to the present invention is a lead-containing composite oxide which is expressed in a general formula aPb x (Cr y Nb 1-x )O 3 -bPb x TiO 3 -cPb x ZrO 3 , with a, b and c being in the following ranges respectively: 1.0 ≤ a ≤ 12.0 40.5 ≤ b ≤ 49.0 39.0 ≤ c ≤ 58.5 where a, b and c are in units of mole % and a + b + c = 100 , and x and y being in the following ranges respectively: 0.95 ≤ x ≤ 1.01 2/24 ≤ y ≤ 11/24 The value of the component a in aPb x (Cr y Nb 1-y )O 3 is selected from the range of 1.0 ≤ a ≤ 12.0, preferably from the range of 2.0 ≤ a ≤ 10.0, and more preferably from the range of 3.0 ≤ a ≤ 9.0. If the value of a is too small or large, the electromechanical coupling factor and the dielectric constant are reduced and the mechanical quality factor is increased. The value of the component b in bPb x TiO 3 is selected from the range of 40.5 ≤ b ≤ 49.0, preferably from the range of 43.0 ≤ b ≤ 48.0, and more preferably from the range of 43.0 ≤ b ≤ 47.0. If the value of b is too small or large, the electromechanical coupling factor and the dielectric constant are reduced. The value of the component c in cPb x ZrO 3 is selected from the range of 39.0 ≤ c ≤ 58.5, preferably from the range of 47.0 ≤ c ≤ 52.0, and more preferably from the range of 48.0 ≤ c ≤ 52.0. If the value of c is too small or large, the electromechanical coupling factor and the dielectric constant are reduced and the mechanical quality factor is increased. The value x indicating the rate of the Pb component is selected from the range of 0.95 ≤ x ≤ 1.01, preferably from the range of 0.96 ≤ x ≤ 1.00. If the value of x is too small or large, the electromechanical coupling factor and the dielectric constant are reduced. The value of y indicating the ratio of Cr to Nb is selected from the range of 2/24 ≤ y ≤ 11/24, preferably from the range of 5/24 ≤ y ≤ 10.5/24, and more preferably from the range of 6/24 ≤ y ≤ 10/24. If the value of y is too small or large, the electromechanical coupling factor and the dielectric constant are reduced and the mechanical quality factor is increased. In the piezoelectric porcelain according to the present invention, not more than 11 mole %, preferably not more than 5 mole %, of the Pb component can be substituted by at least one element of Sr, Ba and Ca. If the amount of the substituted Pb component is too large, the electromechanical coupling factor is reduced. It is possible to attain piezoelectric porcelain having a large electromechanical coupling factor, a small mechanical quality factor and a large dielectric constant by substituting the Pb component in the aforementioned range. According to the present invention, it is possible to obtain piezoelectric porcelain having piezoelectricity with a large electromechanical coupling factor, a small mechanical quality factor and a large dielectric constant, thereby broadening the band. Thus, the piezoelectric porcelain according to the present invention can be applied to a speaker, a microphone, a buzzer or a sensor. The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Lead oxide, zirconium oxide, titanium oxide, chromium oxide and niobium oxide were prepared as raw materials, and mixed with each other at composition ratios shown in Tables 1 to 3. The mixed raw materials were wet-blended in a ball mill, demineralized, dried, and calcined at 800 to 1000°C for 2 hours. The calcined powder materials were again wet-blended in a ball mill, thereby preparing powder materials. Then, caking additives such as water or polyvinyl alcohol were added to the powder materials, which in turn were press-molded and thereafter fired at 1110 to 1320°C for 2 hours, thereby obtaining sintered bodies. The obtained sintered bodies were polished into discs of 10 mm in diameter and 1 mm in thickness, and silver electrodes were baked on both end surfaces of the discs. These discs were polarized in insulating oil of 60 to 80°C for 10 to 60 minutes in electric fields of 2.5 to 4 kV/mm, to obtain piezoelectric porcelain samples. Sample No. aPb x (Cr y Nb 1-y )O 3 -bPb x TiO 3 -cPb x ZrO 3 a mol% b mol% c mol% x Substitutional Element for Pb (mol%) y Sr Ba Ca 1* 5.0 40.0* 55.0 1.00 0.0 0.0 0.0 8/24 2 5.0 40.5 54.5 1.00 0.0 0.0 0.0 8/24 3 5.0 45.5 49.5 1.00 0.0 0.0 0.0 8/24 4 5.0 49.0 46.0 1.00 0.0 0.0 0.0 8/24 5* 5.0 50.0* 45.0 1.00 0.0 0.0 0.0 8/24 6* 5.0 45.5 49.5 0.94* 0.0 0.0 0.0 8/24 7 5.0 45.5 49.5 0.95 0.0 0.0 0.0 8/24 8 5.0 45.5 49.5 1.01 0.0 0.0 0.0 8/24 9* 5.0 45.5 49.5 1.02* 0.0 0.0 0.0 8/24 10* 0.5* 45.5 54.0 1.00 0.0 0.0 0.0 8/24 11 1.0 45.5 53.5 1.00 0.0 0.0 0.0 8/24 12 12.0 45.5 42.5 1.00 0.0 0.0 0.0 8/24 13* 13.0* 45.5 41.5 1.00 0.0 0.0 0.0 8/24 14* 1.0 40.0* 59.0* 1.00 0.0 0.0 0.0 8/24 15* 1.0 50.0* 49.0 1.00 0.0 0.0 0.0 8/24 16* 12.0 40.0* 48.0 1.00 0.0 0.0 0.0 8/24 17* 12.0 50.0* 38.0* 1.00 0.0 0.0 0.0 8/24 18* 5.0 45.5 49.5 1.00 0.0 0.0 0.0 1/24* 19 5.0 45.5 49.5 1.00 0.0 0.0 0.0 2/24 20 5.0 45.5 49.5 1.00 0.0 0.0 0.0 8/24 21 5.0 45.5 49.5 1.00 0.0 0.0 0.0 11/24 22* 5.0 45.5 49.5 1.00 0.0 0.0 0.0 12/24* Sample No. aPb x (Cr y Nb 1-y )O 3 -bPb x TiO 3 -cPb x ZrO 3 a mol% b mol% c mol% x Substitutional Element for Pb (mol%) y Sr Ba Ca 23* 5.0 40.0* 55.0 0.99 2.0 0.0 0.0 8/24 24 5.0 40.5 54.5 0.99 2.0 0.0 0.0 8/24 25 5.0 43.5 51.5 0.99 2.0 0.0 0.0 8/24 26 5.0 44.5 50.5 0.99 2.0 0.0 0.0 8/24 27 5.0 46.5 48.5 0.99 2.0 0.0 0.0 8/24 28 5.0 47.5 47.5 0.99 2.0 0.0 0.0 8/24 29 5.0 49.0 46.0 0.99 2.0 0.0 0.0 8/24 30* 5.0 50.0* 45.0 0.99 2.0 0.0 0.0 8/24 31* 5.0 45.5 49.5 0.94* 2.0 0.0 0.0 8/24 32 5.0 45.5 49.5 0.95 2.0 0.0 0.0 8/24 33 5.0 45.5 49.5 0.96 2.0 0.0 0.0 8/24 34 5.0 45.5 49.5 0.98 2.0 0.0 0.0 8/24 35 5.0 45.5 49.5 1.00 2.0 0.0 0.0 8/24 36 5.0 45.5 49.5 1.01 2.0 0.0 0.0 8/24 37* 5.0 45.5 49.5 1.02* 2.0 0.0 0.0 8/24 38* 0.5* 45.5 54.0 0.99 2.0 0.0 0.0 8/24 39 1.0 45.5 53.5 0.99 2.0 0.0 0.0 8/24 40 3.0 45.5 51.5 0.99 2.0 0.0 0.0 8/24 41 7.0 45.5 47.5 0.99 2.0 0.0 0.0 8/24 42 9.0 45.5 45.5 0.99 2.0 0.0 0.0 8/24 43 12.0 45.5 42.5 0.99 2.0 0.0 0.0 8/24 44* 13.0* 45.5 41.5 0.99 2.0 0.0 0.0 8/24 45* 1.0 40.0* 59.0* 0.99 2.0 0.0 0.0 8/24 46* 1.0 50.0* 49.0 0.99 2.0 0.0 0.0 8/24 47* 12.0 40.0* 48.0 0.99 2.0 0.0 0.0 8/24 48* 12.0 50.0* 38.0* 0.99 2.0 0.0 0.0 8/24 49* 5.0 45.5 49.5 0.99 2.0 0.0 0.0 1/24* 50 5.0 45.5 49.5 0.99 2.0 0.0 0.0 2/24 51 5.0 45.5 49.5 0.99 2.0 0.0 0.0 4/24 52 5.0 45.5 49.5 0.99 2.0 0.0 0.0 6/24 53 5.0 45.5 49.5 0.99 2.0 0.0 0.0 8/24 54 5.0 45.5 49.5 0.99 2.0 0.0 0.0 10/24 55 5.0 45.5 49.5 0.99 2.0 0.0 0.0 11/24 56* 5.0 45.5 49.5 0.99 2.0 0.0 0.0 12/24* Sample No. aPb x (Cr y Nb 1-y )O 3 -bPb x TiO 3 -cPb x ZrO 3 a mol% b mol% c mol% x Substitutional Element for Pb (mol%) y Sr Ba Ca 57 5.0 45.5 49.5 0.99 4.0 0.0 0.0 8/24 58 5.0 45.5 49.5 0.99 6.0 0.0 0.0 8/24 59 5.0 45.5 49.5 0.99 8.0 0.0 0.0 8/24 60 5.0 45.5 49.5 0.99 11.0 0.0 0.0 8/24 61* 5.0 45.5 49.5 0.99 12.0* 0.0 0.0 8/24 62 5.0 45.5 49.5 0.99 0.0 2.0 0.0 8/24 63 5.0 45.5 49.5 0.99 0.0 6.0 0.0 8/24 64 5.0 45.5 49.5 0.99 0.0 11.0 0.0 8/24 65* 5.0 45.5 49.5 0.99 0.0 12.0* 0.0 8/24 66 5.0 45.5 49.5 0.99 0.0 0.0 2.0 8/24 67 5.0 45.5 49.5 0.99 0.0 0.0 6.0 8/24 68 5.0 45.5 49.5 0.99 0.0 0.0 11.0 8/24 69* 5.0 45.5 49.5 0.99 0.0 0.0 12.0* 8/24 70 5.0 45.5 49.5 0.99 3.0 3.0 0.0 8/24 71 5.0 45.5 49.5 0.99 3.0 0.0 3.0 8/24 72 5.0 45.5 49.5 0.99 0.0 3.0 3.0 8/24 73 5.0 45.5 49.5 0.99 4.0 4.0 3.0 8/24 74* 5.0 45.5 49.5 0.99 4.0* 4.0* 4.0* 8/24 Referring to Tables 1 to 3, asterisked numerals denote comparative samples which are out of the inventive ranges. Referring to comparative samples, composition ratios of asterisked components are out of the inventive ranges. Dielectric constants (ε 33 T /ε 0 ), electromechanical coupling factors (Kp) of vibration in expansion directions, and mechanical quality factors (Qm) were measured as to the obtained piezoelectric porcelain samples. An impedance measuring device was employed to measure the dielectric constants at a measuring frequency of 1 kHz while measuring the electromechanical coupling factors of the vibration in the expansion directions by a resonance/antiresonance method. Tables 4 to 6 show the results. Sample No. Electric Characteristics ε 33 T /ε 0 Kp (%) Qm 1* 320 50.6 152 2 405 53.3 144 3 2073 65.2 131 4 1041 53.4 172 5* 689 48.6 183 6* 996 51.7 183 7 1523 55.4 174 8 1786 53.2 99 9* 1359 39.6 52 10* 312 48.2 437 11 841 54.7 346 12 1703 55.0 106 13* 1442 51.9 121 14* 249 49.5 369 15* 641 47.1 426 16* 309 50.6 141 17* 577 47.6 164 18* 1391 49.5 258 19 1681 53.5 174 20 2073 66.7 114 21 1658 57.7 334 22* 1546 54.5 408 Sample No. Electric Characteristics ε 33 T /ε 0 Kp (%) Qm 23* 490 52.5 130 24 521 54.6 125 25 1128 68.8 122 26 2014 70.0 118 27 1900 62.6 143 28 1584 58.5 153 29 1186 54.8 157 30* 852 50.3 161 31* 1154 53.3 161 32 1671 56.7 158 33 1802 59.4 155 34 2061 63.8 146 35 2196 66.5 114 36 1933 53.8 79 37* 1517 39.6 32 38* 454 49.5 426 39 982 54.7 331 40 2224 67.6 183 41 2128 64.2 130 42 2019 58.9 124 43 1703 55.0 106 44* 1598 53.5 103 45* 403 51.2 355 46* 794 48.7 405 47* 451 51.9 119 48* 726 49.2 151 49* 1547 51.2 246 50 1826 54.9 155 51 2104 59.8 104 52 2192 63.6 107 53 2223 66.7 114 54 2038 62.2 209 55 1814 58.9 318 56* 1695 54.5 392 Sample No. Electric Characteristics ε 33 T /ε 0 Kp (%) Qm 57 2204 63.8 145 58 2253 58.1 154 59 2261 57.0 155 60 2569 55.1 151 61* 2581 53.8 153 62 2146 66.2 112 63 2165 57.5 149 64 2310 54.8 152 65* 2344 53.1 153 66 2042 65.3 101 67 2067 56.8 139 68 2322 54.6 143 69* 2359 52.7 145 70 2204 57.9 153 71 2159 57.3 147 72 2098 57.2 123 73 2306 54.6 150 74* 2339 52.9 155 As to the value of a in the general formula, it is understood possible to obtain piezoelectric porcelain having a large electromechanical coupling factor, a small mechanical quality factor and a high dielectric constant in the inventive range, particularly from the test data of the samples Nos. 10 to 13 and 38 to 44. As to the values of b and c in the general formula, it is understood possible to obtain piezoelectric porcelain having a large electromechanical coupling factor, a small mechanical quality factor and a high dielectric constant in the inventive ranges, particularly from the test data of the samples Nos. 1 to 5, 14 to 17, 23 to 30 and 45 to 48. As to the value of x in the general formula, it is understood possible to obtain piezoelectric porcelain having a large electromechanical coupling factor, a small mechanical quality factor and a high dielectric constant in the inventive range, particularly from the test data of the samples Nos. 6 to 9 and 31 to 37. As to the value of y in the general formula, it is understood possible to obtain piezoelectric porcelain having a large electromechanical coupling factor, a small mechanical quality factor and a high dielectric constant in the inventive range, particularly from the test data of the samples Nos. 18 to 22 and 49 to 56. As to the rate of substitution of the Pb component by Sr, Ba or Ca, it is understood possible to obtain piezoelectric porcelain having a large electromechanical coupling factor, a small mechanical quality factor and a high dielectric constant in the inventive range, particularly from the test data of the samples Nos. 57 to 74. Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the scope of the present invention being limited only by the terms of the appended claims.

Claims: Piezoelectric porcelain, being a lead-containing composite oxide expressed in a general formula aPb x (Cr y Nb 1-y )O 3 -bPb x TiO 3 -cPb x ZrO 3 , with a, b and c being in the following ranges respectively: 1.0 ≤ a ≤ 12.0 40.5 ≤ b ≤ 49.0 39.0 ≤ c ≤ 58.5 where a, b and c are in units of mole % and a + b + c = 100, and x and y being in the following ranges respectively: 0.95 ≤ x ≤ 1.01 2/24 ≤ y ≤ 11/24 The piezoelectric porcelain in accordance with claim 1, wherein the value of a is in the range of 2.0 ≤ a ≤ 10.0. The piezoelectric porcelain in accordance with claim 1, wherein the value of b is in the range of 43.0 ≤ b ≤ 48.0. The piezoelectric porcelain in accordance with claim 1, wherein the value of c is in the range of 47.0 ≤ c ≤ 52.0. The piezoelectric porcelain in accordance with claim 1, wherein the value of x is in the range of 0.96 ≤ x ≤ 1.00. The piezoelectric porcelain in accordance with claim 1, wherein the value of y is in the range of 5/24 ≤ y ≤ 10.5/24. The piezoelectric porcelain in accordance with claim 1, wherein not more than 11 mole % of said Pb component is substituted by at least one element of Sr, Ba and Ca. The piezoelectric porcelain in accordance with claim 1, wherein not more than 5 mole % of said Pb component is substituted by at least one element of Sr, Ba and Ca.

Inventors: KIMURA MASANORI, SUBE MITSURU, KIMURA, MASANORI, SUBE, MITSURU
Applicants: MURATA MANUFACTURING CO, MURATA MANUFACTURING CO., LTD.
Application year: 1995
Main classification: C04B35
IPC codes: H01L41, C04B35