Abstract:
A piezoelectric contains comprises a plurality of piezoelectric particles made from a piezoelectric material such as lead titanate zirconate and a dielectric made from a dielectric material, such as a composite perovskite compound, having a higher dielectric constant then the piezoelectric material, the dielectric existing in gaps between the piezoelectric particles. When poling to produce a piezoelectric ceramic, the poling is uniformly performed, and nearly all of the electric field is applied to the piezoelectric particles. Thus, the dispersion of the piezoelectric properties can be reduced, and the piezoelectric properties can be enhanced.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a piezoelectric ceramic, a method of producing the same, and a piezoelectric part and more particularly to a technique by which the piezoelectric properties of a piezoelectric ceramic can be enhanced and the dispersion of the piezoelectric properties can be reduced.  
           [0003]    2. Description of the Related Art  
           [0004]    Referring to a technique interesting to the present invention, Japanese Unexamined Patent Application Publication No. 4-295051 (Patent Document 1) describes a PZT type ceramic composition in which bismuth sodium titanate is added to a PZT type material represented by the following chemical formula: Pb 1.01 (Zr 0.53 Ti 0.47 ) O 3 +0.5 mol % Nb 2 O 5  in an amount of not less than 0.5% by weight to less than 5% by weight based on 100% by weight of the PZT type material.  
           [0005]    The known technique described in Patent Document 1 has the object of enhancing the mechanical strength of a piezoelectric ceramic without the functional characteristics of the piezoelectric ceramic being damaged. To achieve the above-described object, according to the known technique, a bismuth sodium titanate with a piezoelectric property is selected as an additive which can form a liquid phase at the same temperature as the firing temperature of the PZT type material and also has the same functional properties as those of the PZT type material. The additive is added, and forms a liquid phase when the PZT type material is fired. Thus, the PZT type material is sintered in a liquid phase.  
           [0006]    Referring to another technique interesting to the present invention, Japanese Unexamined Patent Application Publication No. 11-87792 (Patent Document 2) describes a piezoelectric ceramic having a composite structure, in which at least two regions having different compositional ratios or different compositions exist. One of the two regions is a region in which the properties of the piezoelectric ceramic are prominent, and the other is a region in which the properties of an electrostrictive ceramic are prominent.  
           [0007]    The known technique described in Patent Document 2 has the object of providing a piezoelectric ceramic of which the electric field—strain characteristic is controlled so as to be linear. To achieve this object, according to the known technique, materials with different piezoelectric properties are processed to form a composite. In particular, one of the materials forms a region in which the properties of a piezoelectric ceramic are prominent, and the other material forms a region in which the properties of an electrostrictive ceramic are prominent. Thereby, the piezoelectric characteristics can be easily controlled. As a result, the electric field—strain characteristic can be controlled.  
           [0008]    However, the techniques described in Patent Documents 1 and 2 have the following problems.  
           [0009]    According to the technique of Patent Document 1, the PZT type material to which bismuth sodium titanate is added is sintered in the liquid phase. Therefore, the PZT type material can be sintered at low temperature. However, the properties of the sintered piece may be dispersed, since the sintering is not uniform in the case of sintering in a liquid phase. Moreover, since bismuth sodium titanate has a lower dielectric constant than the PZT type material, a voltage can not be sufficiently applied to the sintered PZT type material in some cases, when the PZT type material is poled. Thus, regarding the poled piezoelectric piece, the piezoelectric properties can not be sufficiently realized in some cases.  
           [0010]    According to the technique described in Patent Document 2, two-type regions are formed. In particular, two types of powdery materials with different composition ratios or compositions are respectively granulated. The granulated particles are mixed, formed and fired. However, when the granulated particles with different composition ratios or compositions are mixed and fired, the sintering tends to become irregular. Therefore, the piezoelectric properties are deteriorated or dispersed to a large degree in some cases.  
         SUMMARY OF THE INVENTION  
         [0011]    Accordingly, it is an object of the present invention to provide a piezoelectric ceramic, a method of producing the same, and a piezoelectric part which can solve the above-described problems.  
           [0012]    According to a first aspect of the present invention, there is provided a piezoelectric ceramic which includes a plurality of piezoelectric particles made from a piezoelectric material and a dielectric made from a dielectric material having a higher dielectric constant than the piezoelectric material, with the dielectric existing in gaps between the piezoelectric particles.  
           [0013]    Preferably, the piezoelectric material is one of lead titanate zirconate, lead titanate, lead titanate zirconate containing a composite perovskite compound as a solid solution, and lead titanate containing a composite perovskite compound as a solid solution. Also, preferably, the dielectric material is one of a composite perovskite compound, a solid solution made from a composite perovskite compound and lead titanate, and an oxide for enhancement of a dielectric constant added to a piezoelectric material.  
           [0014]    According to a second aspect of the present invention, there is provided a method of producing a piezoelectric ceramic which includes: a first step of calcining a powdery compound raw material for a piezoelectric material so that a calcined powder for use as the piezoelectric material is produced; a second step of calcining a powdery compound raw material for a dielectric material having a higher dielectric constant than the piezoelectric material so that a calcined powder for use as the dielectric material having a smaller particle size than the calcined powder for use as the piezoelectric material is produced; a third step of mixing the calcined powder for use as the piezoelectric material with the calcined powder for use as the dielectric material so that mixed powder is produced; a fourth step of forming the mixed powder into a predetermined shape so that a formed piece is produced; and a fifth step of firing the formed piece so that a sintered piece as a piezoelectric ceramic is produced. In general, the dielectric constant of the piezoelectric will preferably be about to and the dielectric constant of the dielectric will preferably be about to, with the difference between the two dielectric constants being preferably at least about.  
           [0015]    In the method of the present invention, the calcined powder for use as the dielectric material preferably has a particle size which is not more than about one fourth of the particle size of the calcined powder for use as the piezoelectric material (the particle size of the calcined powder for use as the dielectric material excludes zero). More preferably, the calcined powder for use as the dielectric material preferably has a particle size which is about to of the particle size of the calcined powder for use as the piezoelectric material  
           [0016]    In the third step, the calcined powder for use as the dielectric material is mixed with the calcined powder for use as the piezoelectric material in an amount which is preferably not more than about 3 parts by weight based on 100 parts by weight of the calcined powder for use as the piezoelectric material (the amount of the calcined powder for use as the dielectric material excludes zero). More preferably, the ount of the dielectric material is about to parts by weight based on 100 parts of the piezoelectric powder.  
           [0017]    Moreover, the present invention is intended for a piezoelectric part which includes a major piece thereof made from the above-described piezoelectric ceramic and an external electrode formed on an outer surface of the major piece of the piezoelectric part.  
           [0018]    As described above, a dielectric made from a dielectric material having a higher dielectric constant than a piezoelectric material exists in the gaps between a plurality of piezoelectric particles made from the piezoelectric material in the piezoelectric ceramic of the present invention. Accordingly, the whole of the piezoelectric ceramic can be uniformly poled, and nearly all of the electric field is applied to the piezoelectric particles. Thus, the dispersion of the piezoelectric characteristics can be reduced, and moreover, the piezoelectric characteristics can be enhanced.  
           [0019]    As a result, the yield of the method of producing the piezoelectric part using the piezoelectric ceramic of the present invention is enhanced, and the production efficiency is also improved.  
           [0020]    In the method of producing the piezoelectric ceramic of the present invention, the calcined powder for use as the dielectric material preferably has a particle size which is not more than about one fourth of the particle size of the calcined powder for use as the piezoelectric material (the particle size of the calcined powder for use as the dielectric material excludes zero). Therefore, the dispersions of the piezoelectric properties such as the resonance frequency and the anti-resonance frequency are significantly reduced.  
           [0021]    Also,the calcined powder for use as the dielectric material is mixed with the calcined powder for use as the piezoelectric material preferably in an amount not more than about 3 parts by weight based on 100 parts by weight of the calcined powder for use as the piezoelectric material (the amount of the calcined powder for use as the dielectric material excludes zero) in the method of producing the piezoelectric ceramic of the present invention. Therefore, the piezoelectric properties such as the electromechanical coupling factor or the like are prevented from deteriorating. In some cases, piezoelectric properties can be enhanced. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 is a cross-sectional view of an example of a piezoelectric part formed using the piezoelectric ceramic of the present invention;  
         [0023]    [0023]FIG. 2 illustrates, in cross-section, the structure of the piezoelectric ceramic constituting the major piece of the electric part; and  
         [0024]    [0024]FIG. 3A and FIG. 3B illustrate an example of the method of producing a piezoelectric ceramic according to the present invention;  
         [0025]    [0025]FIG. 3A illustrates, in a cross-section, mixed powder obtained by mixing of calcined powder for use as the piezoelectric material with calcined powder for use as the dielectric material; and  
         [0026]    [0026]FIG. 3B illustrates, in a cross section, a sintered piece obtained by forming the mixed powder into a predetermined shape and firing the formed piece. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    The piezoelectric part formed using the piezoelectric ceramic of the present invention may have different structures. FIG. 1 shows an example of the piezoelectric part having the simplest structure.  
         [0028]    A piezoelectric part  1  shown in FIG. 1 contains a sheet-shaped major piece  2  and external electrodes  3  and  4  formed on the outer faces opposite to each other of the major piece  2 . The external electrodes  3  and  4  are formed by applying electro-conductive paste containing silver as an electro-conductive ingredient on the respective end faces, and baking the paste.  
         [0029]    In the case of the piezoelectric part  1  shown in FIG. 1, the external electrodes  3  and  4  are used not only as terminals for input-output of voltage to or from the major piece  2  but also as terminals through which a DC electric field is applied to the whole of a sintered piece to be the major piece  2 , resulting in production of a piezoelectric ceramic.  
         [0030]    The piezoelectric ceramic  11  constituting the major piece  2  of the piezoelectric part  1  has a structure as shown in FIG. 2. In particular, the piezoelectric ceramic  11  comprises a plurality of piezoelectric particles  12  made from a piezoelectric material and a dielectric  13  made from a dielectric material having a higher dielectric constant than the piezoelectric material. The dielectric exists in the gaps between the piezoelectric particles  12 .  
         [0031]    For example, the above-described piezoelectric material is preferably one of lead titanate zirconate, lead titanate, lead titanate zirconate containing a composite perovskite compound as a solid solution, and lead titanate containing a composite perovskite compound as a solid solution. Preferably, the above-described dielectric material is one of a composite perovskite compound, a solid solution made from a composite perovskite compound and lead titanate, and an oxide for enhancement of a dielectric constant added to a piezoelectric material.  
         [0032]    Preferably, the above-described piezoelectric ceramic  11  is produced as follows.  
         [0033]    Referring to FIG. 3A, plural raw materials for a piezoelectric material are mixed to form a powdery compound raw material. The powdery compound raw material is calcined. Thus, calcined powder  14  for use as the piezoelectric material is prepared. On the other hand, plural raw materials for a dielectric material having a higher dielectric constant than the piezoelectric material are mixed to form a powdery compound raw material. Then, the powdery compound raw material is calcined. Thus, calcined power  15  for use as the dielectric material is prepared. In this case, the particle size of the calcined powder  15  for use as the dielectric material is smaller than that of the calcined powder  14  for use as the dielectric material. Preferably, the calcined powder  15  for use as the dielectric material is not more than about one fourth of the particle size of the calcined powder  14  for use as the piezoelectric material (the particle size of the calcined powder excludes 0).  
         [0034]    Subsequently, the calcined powder  14  for the piezoelectric material is mixed with the calcined powder  15  for the dielectric material. Thus, mixed powder  16 , as shown in FIG. 3A, is prepared. Preferably, not more than about 3 parts by weight of the calcined powder  15  for use as the dielectric material is mixed with 100 parts by weight of the calcined powder  14  for use as the piezoelectric material (the amount of the calcined powder  15  excludes 0) in the mixing process.  
         [0035]    Then, the mixed powder  16  is formed in such a manner as to produce a formed piece having the same shape as that of the major piece  2  shown in FIG. 1. For the formation of the mixed powder  16 , for example, a binder such as water or polyvinylalcohol is added to the mixed powder  16 , and the resulting material is press-formed or the like.  
         [0036]    Subsequently, the formed piece is fired. Thus, a sintered piece  17  as shown in FIG. 3B is formed. The sintered piece  17  has substantially the same shape as the major piece  2  shown in FIG. 2. It is to be noted that the sintered piece  17  may be abraded to have the shape identical to the major piece  2 , if necessary.  
         [0037]    Subsequently, external electrodes  3  and  4  are formed on both of the end-faces of the sintered piece  17 . Thereafter, the sintered piece  17  is poled. In particular, a DC field is applied to the sintered piece  17  via the external electrodes  3  and  4 . As a result, the sintered piece  17  is converted to the piezoelectric ceramic  11  shown in FIG. 2 having a piezoelectric property shown in FIG. 2. Thus, the piezoelectric part  1  containing the major piece  2  made of the piezoelectric ceramic  11  as shown in FIG. 1 is produced.  
         [0038]    Hereinafter, Examples will be described, which were carried out to identify the operation and effects of the present invention.  
       EXAMPLE 1  
       [0039]    As powdery compound raw materials for a piezoelectric material, powders of lead oxide, zirconium oxide, titanium oxide, strontium carbonate, magnesium hydroxide and chromium oxide were prepared. These powders were compounded in such amounts that lead titanate zirconate having a composition represented by the following formula: Pb 0.93 Mg 0.02 Sr 0.05 (Zr 0.54 Ti 0.46 )O 3 +0.5 weight % Cr 2 O 3  could be obtained. The compounded powdery compound raw materials were wet-mixed by means of a ball mill. Then, water was removed, and the powdery compound raw materials were dried and calcined at a temperature of 850 to 950° C. for 2 hours. The calcined powder was wet-crushed by means of a ball mill. Thus, a calcined powder for use as the piezoelectric material having an average particle size of 1.6 μm was formed.  
         [0040]    As powdery compound raw materials for a dielectric material, powders of lead oxide, magnesium hydroxide and niobium oxide were prepared. The powders were compounded in such amounts that a composite perovskite compound having a composition represented by the following formula: Pb(Mg 1/3 Nb 2/3 )O 3  could be formed. The compounded powdery compound raw materials were mixed by means of a ball mill. Water was removed from the mixed powder, and then the powder was calcined at a temperature of 800 to 900° C. for 2 hours. The calcined powder was wet-crushed by means of a ball mill. Thus, a calcined powder with an average particle size of 0.2 μm for use as the dielectric material was formed. In this case, the wet-mixing conditions and the calcining temperature were set so that the particle size of the calcined powder for use as the dielectric material would be smaller than that of the calcined powder for use as the piezoelectric material.  
         [0041]    Thereafter, the calcined powder for use as the dielectric material was mixed with the calcined power for use as the piezoelectric material in amounts of 0, 0.05, 0.2, 1, 3, and 5 parts by weight, respectively, based on 100 parts by weight of the calcined powder for use as the piezoelectric material. Thus, the mixed powders to form samples 1 to 7 were produced.  
         [0042]    Subsequently, polyvinylalcohol as a binder was added to each of the mixed powders, the composition was formed by pressing, and fired at a temperature of 1150 to 1250° C. for 2 hours. Thus, sintered pieces were produced.  
         [0043]    Subsequently, each sintered piece was abraded to form a disk with a diameter of 10 mm and a thickness of 1 mm. External electrodes containing silver as an electroconductive ingredient were formed on both of the end-faces of the disk-shaped sintered piece by baking of electroconductive paste.  
         [0044]    Then, the sintered piece was processed to be polarized. In particular, the sintered piece having the external electrodes formed thereon as described above was placed in insulating-oil whose temperature was maintained at 60° C. A DC electric field with an intensity of 3 kV/mm was applied between the external electrodes for 30 minutes. Thus, the entire sintered piece was poled so as to have a piezoelectric property.  
         [0045]    As described above, piezoelectric parts each comprising the major piece made from the piezoelectric ceramic and the external electrodes were prepared and taken as samples.  
         [0046]    Subsequently, regarding the piezoelectric part samples, the electromechanical coupling factors (Kp) with respect to vibration in the radial direction were measured. Moreover, the dispersions (CV-fr) of the resonance frequencies (fr) and the dispersions (CV-fa) of the anti-resonance frequencies (fa) of radial vibration were determined. In the above-description, CV represents an average value of the standard deviation. Table 1 shows the measurement results.  
                                                     TABLE 1                           CALCINED POWDER                       FOR USE AS       SAMPLE   DIELECTRIC MATERIAL   Kp   CV-fr   CV-fa       NO.   (PARTS BY WEIGHT)   (%)   (ppm)   (ppm)                                1   0   42.1   1050   2030       2   0.05   43.9   650   1050       3   0.2   44.5   320   520       4   1   44.5   240   420       5   3   43.8   310   540       6   5   38.5   620   1030       7   5.5   36   720   1250                  
 
         [0047]    A seen in Table 1, the dispersions (CV-fr) of the resonance frequencies (fr) and the dispersions (CV-fa) of the anti-resonance frequencies (fa) of samples 2 to 7 containing the calcined powder for use as the dielectric material are smaller than that of sample 1 which does not contain the calcined material for use as the dielectric material.  
         [0048]    Moreover, the electromechanical coupling factors (Kp) of the samples 2 to 5 containing not more than about 3 parts by weight of the calcined powder for use as the dielectric material based on 100 parts by weight of the calcined powder for use as the piezoelectric material are enhanced compared to those of the sample 1, which does not contain the calcined powder for use as the dielectric material and the samples 6 and 7 which contain more than about 3 parts by weight of the calcined powder for the dielectric material.  
       EXAMPLE 2  
       [0049]    In Example 2, effects of the ratio of the particle sizes of the calcined powder for use as the piezoelectric material to those of the calcined powder for use as the dielectric material were investigated.  
         [0050]    In particular, a calcined powder for use as a piezoelectric material having the same composition and average particle size, i.e., 1.6 μm of the calcined powder for use as the piezoelectric material in Example 1 was prepared. Moreover, calcined powders for use as a dielectric material having the same compositions as the calcined powder for use as the dielectric material and the average particle sizes of 0.1 μm, 0.2 μm, 0.4 μm, 0.5 μm, and 0.8 μm were prepared. Each calcined powder for use as the dielectric material was mixed with the calcined powder for use as the piezoelectric material in an amount of 1 part by weight based on 100 parts by weight of the calcined powder for use as the piezoelectric material. Thus, mixed powders were produced.  
         [0051]    In other respects, piezoelectric parts as respective samples were produced in the same manner as those in Example 1. The measurement was carried out as in Example 1.  
         [0052]    Table 2 shows the results. The term “particle size ratio” used in Table 2 means the ratio of the average particle size of calcined powder for use as the dielectric material to that of calcined powder for use as the piezoelectric material.  
                                                     TABLE 2                       SAMPLE   PARTICLE   Kp   CV-fr   CV-fa       NO.   SIZE RATIO   (%)   (ppm)   (ppm)                                11   0.0625   44.6   220   390       12   0.125   44.5   240   420       13   0.25   40.1   380   680       14   0.3125   37   420   860       15   0.5   30.5   490   1550                  
 
         [0053]    Sample 12 in Table 2 is the same as the sample 4 in Table 1.  
         [0054]    As seen in Table 2, the dispersions (CV-fr) of the resonance frequencies (fr) and the dispersions (CV-fa) of the anti-resonance frequencies (fa) of samples 11 to 13 having a particle size ratio of not more than ¼ (0.25) are smaller compared to les 14 and 15 having a particle size ratio of more than ¼.  
       EXAMPLE 3  
       [0055]    In Example 3, powders of lead oxide, zirconium oxide, titanium oxide, strontium carbonate, magnesium hydroxide, niobium oxide, and chromium oxide were prepared as powdery compound raw materials for a piezoelectric material. Piezoelectric parts were prepared in the same manner as that in Example 1 except that these powders were compounded in such amounts that lead titanate zirconate having a composition represented by the following formula:  
         [0056]    Pb 0.93 Mg 0.03 Sr 0.05 {(Mg 1/3 Nb 2/3 ) 0.05 Zr 0.49 Ti 0.46 }O 3 +0.5 weight % Cr 2 O 3  could be produced, and were taken as samples. The measurement was carried out as in Example 1. Table 3 shows the results.  
                                                     TABLE 3                           CALCINED POWDER                       FOR USE AS       SAMPLE   DIELECTRIC MATERIAL   Kp   CV-fr   CV-fa       NO.   (PARTS BY WEIGHT)   (%)   (ppm)   (ppm)                                21   0   50.9   650   1350       22   0.05   50.9   420   850       23   0.2   51.2   310   500       24   1   51.8   200   320       25   3   50.9   240   390       26   5   48.4   460   770       27   5.5   46.3   530   920                  
 
         [0057]    As seen in Table 3, the same tendency as that shown in Table 1 of Example 1 is exhibited in this Example 3.  
         [0058]    In particular, the dispersions (CV-fr) of the resonance frequencies (fr) and the dispersions (CV-fa) of the anti-resonance frequencies (fa) of samples 22 to 27 containing the calcined powder for use as the dielectric material are smaller compared to those of sample 21 not containing the calcined material for use as the dielectric material.  
         [0059]    Moreover, the electromechanical coupling factors (Kp) of the samples 22 to 25 containing not more than about 3 parts by weight of the calcined powder for use as the dielectric material based on 100 parts by weight of the calcined powder for use as the piezoelectric material are enhanced compared to those of the samples 26 and 27 containing more than about 3 parts by weight of the calcined powder for use as the dielectric material.  
       EXAMPLE 4  
       [0060]    In Example 4, piezoelectric parts were prepared in the same manner as that of Example 1 except that a solid solution as a dielectric material made from a composite perovskite compound and lead titanate, the solid solution having a composition represented by the following formula: Pb{(Mg 1/3 Nb 2/3 ) 0.95 Ti 0.05 )O 3 }, and were used to prepare samples. The measurement was carried out as in Example 1. Table 4 shows the results.  
                                                     TABLE 4                           CALCINED POWDER                       FOR USE AS       SAMPLE   DIELECTRIC MATERIAL   Kp   CV-fr   CV-fa       NO.   (PARTS BY WEIGHT)   (%)   (ppm)   (ppm)                                31   0   42.1   1050   2030       32   0.05   44.1   560   950       33   0.2   44.9   310   480       34   1   45.1   220   400       35   3   44.1   290   490       36   5   39.5   580   990       37   5.5   36.5   690   1190                  
 
         [0061]    As seen in Table 4the same tendency as that in Table 1 of Example 1 is exhibited in this Example 4.  
         [0062]    In particular, the dispersions (CV-fr) of the resonance frequencies (fr) and the dispersions (CV-fa) of the anti-resonance frequencies (fa) of samples 32 to 37 containing the calcined powder for the dielectric material are smaller compared to those of sample 31 not containing the calcined material for use as the dielectric material.  
         [0063]    Moreover, the electromechanical coupling factors (Kp) of the samples 32 to 35 containing not more than 3 parts by weight of the calcined powder for use as the dielectric material based on 100 parts by weight of the calcined powder for use as the piezoelectric material are enhanced compared to those of the sample 31 not containing the calcined powder for use as the dielectric material and the samples 36 and 37 which contain more than about 3 parts by weight of the calcined powder for use as the dielectric material.  
       EXAMPLE 5  
       [0064]    In Example 5, piezoelectric parts were prepared in the same manner as that in Example 1 except that 0.5% by weight of Nb 2 O 3  of an oxide for enhancement of a dielectric constant added to a piezoelectric material having a composition represented by the following formula: Pb 0.95 Sr 0.05 (Zr 0.54 Ti 0.46 )O 3  and was used to prepare the dielectric material was used as a dielectric material, and were taken as samples. The measurement was carried out as in Example 1. Table 5 shows the results  
                                                     TABLE 5                           CALCINED POWDER                       FOR USE AS       SAMPLE   DIELECTRIC MATERIAL   Kp   CV-fr   CV-fa       NO.   (PARTS BY WEIGHT)   (%)   (ppm)   (ppm)                                41   0   42.1   1050   2030       42   0.05   43.9   860   1350       43   0.2   44.2   680   1150       44   1   44.2   580   870       45   3   43.5   670   1050       46   5   42.9   900   1650       47   5.5   42.3   940   1880                  
 
         [0065]    As seen in Table 5, the same tendency as that in Table 1 of Example 1 is exhibited in this Example 5.  
         [0066]    In particular, the dispersions (CV-fr) of the resonance frequencies (fr) and the dispersions (CV-fa) of the anti-resonance frequencies (fa) of samples 42 to 47 containing the calcined powder for use as the dielectric material are smaller compared to those of sample 41 not containing the calcined material for use as the dielectric material.  
         [0067]    Moreover, the electromechanical coupling factors (Kp) of the samples 42 to 45 containing not more than about 3 parts by weight of the calcined powder for use as the dielectric material based on 100 parts by weight of the calcined powder for use as the piezoelectric material are enhanced compared to those of the sample 31 not containing the calcined powder for use as the dielectric material and the samples 46 and 47 containing more than about 3 parts by weight of the calcined powder for use as the dielectric material.  
         [0068]    Moreover, a dielectric material to which piezoelectric material was added was used in Example 5. Therefore, although more than about 3 parts by weight of the calcined powder for use as the dielectric material were added in the samples 46 and 47 the electromechanical coupling factors (Kp) are also prevented from decreasing in contrast to the sample 41 not containing the calcined powder for use as the dielectric material. When the dielectric powder contains a piezoelectric component, the powder is preferably used in an amount of less than 6 weight parts per 100 parts of the piezoelectric powder.  
         [0069]    The specific Examples 1 to 5, which were carried out to identify the operation and effects of the present invention, are described hereinbefore. In Examples 1 to 5, different combinations of the piezoelectric materials and the dielectric materials were employed. In particular, the combination of lead titanate zirconate as a piezoelectric material and the perovskite compound as a dielectric material (Examples 1 and 3), the combination of lead titanate zirconate containing the composite perovskite compound as a solid solution as a piezoelectric material and the composite perovskite compound as a dielectric material (Example 2), the combination of lead titanate zirconate as a piezoelectric material and a solid solution, as a dielectric material, made from a composite perovskite compound and lead titanate zirconate (Example 4), and the combination of lead titanate zirconate as a piezoelectric material and an oxide for enhancement of a dielectric constant added to a piezoelectric material (Example 5) were employed. It has been confirmed that the same operation and effects can be also obtained by use of other combinations, piezoelectric materials.