Patent Publication Number: US-7910016-B2

Title: Piezoelectric ceramic composition and piezoelectric ceramic electronic component

Description:
This is a continuation of application Ser. No. 11/517,484, filed Sep. 8, 2006, now U.S. Pat. No. 7,754,095; which is a continuation of PCT/JP2006/306353, filed Mar. 28, 2006, both of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to a piezoelectric ceramic composition and a piezoelectric ceramic electronic component, and more particularly, to a piezoelectric ceramic composition, which does not contain Pb (lead), and a piezoelectric ceramic electronic component that includes the piezoelectric ceramic composition, such as a piezoelectric actuator or a piezoelectric buzzer. 
     BACKGROUND ART 
     In recent years, considering reducing the load on the environment, a lead-free piezoelectric ceramic composition has attracted attention. In general, lead-free piezoelectric ceramic composition is known to have a lower piezoelectric d constant than a lead-based piezoelectric ceramic composition, such as PbTiO 3 —PbZrO 3  (PZT). 
     Under such circumstances, a (K, Na)NbO 3 -based piezoelectric ceramic composition, which has a relatively large piezoelectric d constant (piezoelectric distortion constant) among non-lead piezoelectric ceramic compositions, has been studied actively. 
     For example, Patent Document 1 discloses a piezoelectric ceramic composition containing a main component having a general formula of (1−n)(K 1-x-y Na x Li y ) m (Nb 1-z Ta z )O 3 -nM1M2O 3  (wherein M1 is a bivalent metallic element, and M2 is a quadravalent metallic element). Patent Document 2 discloses a piezoelectric ceramic composition containing a main component having a general formula of (1−n)(K 1-x-y Na x Li y ) m (Nb 1-z Ta z )O 3 -nM1M2M3O 3  (wherein M1 is a trivalent metallic element, M2 is a monovalent metallic element, and M3 is a tetravalent metallic element). In Patent Documents 1 and 2, x, y, z, m, and n are in the ranges of 0.1≦x, y≦0.3, x+y&lt;0.75, 0≦z≦0.3, 0.98≦m≦1.0, and 0&lt;n&lt;0.1. 
     In Patent Documents 1 and 2, a predetermined mol of a complex oxide M1M2O 3  or M1M2M3O 3  (for example, BaTiO 3 , CaTiO 3 , or (Na 0.5 Bi 0.5 )TiO 3 ) of a perovskite type is dissolved as a component in (K, Na, Li)(Nb, Ta)O 3 . The resulting piezoelectric ceramic composition has a relative dielectric constant ∈r (=∈ T /∈ 0 ; ∈ T  is the absolute dielectric constant, and ∈ 0  is the dielectric constant of free space) of at least 1000, an electromechanical coupling factor kp of at least 25%, and a Curie point Tc of more than 200 degrees C. 
     Patent Document 3 discloses a piezoelectric ceramic composition containing 0.005 to 0.15 mol of at least one metallic element selected from the group consisting of Ag, Al, Au, B, Ba, Bi, Ca, Ce, Co, Cs, Cu, Dy, Er, Eu, Fe, Ga, Gd, Ge, Hf, Ho, In, Ir, La, Lu, Mg, Mn, Nd, Ni, Pd, Pr, Pt, Rb, Re, Ru, Sc, Si, Sm, Sn, Sr, Tb, Ti, Tm, V, Y, Yb, Zn and Zr per one mol of a main component having a general formula of {Li x (K 1-y Na y ) 1-x }(Nb 1-z-w Ta z Sb w )O 3  (wherein 0≦x≦0.2, 0≦y≦1, 0&lt;z≦0.4, and 0&lt;w≦0.2) and has a percentage of open pores of 0.4% by volume or less. 
     Patent Document 3 indicates that the addition of the at least one metallic element selected from Ag to Zr described above to reduce the percentage of open pores (the volume percentage of hollows in the surface of a piezoelectric ceramic composition) to 0.4% by volume or less can improve the mechanical strength. In addition, Patent Document 3 indicates that since the piezoelectric ceramic composition contains a component having the general formula of {Li x (K 1-y Na y ) 1-x }(Nb 1-z-w Ta z Sb w )O 3  as a main component, the piezoelectric ceramic composition can utilize a high piezoelectric d constant and a high electromechanical coupling factor kp of the compound having the general formula to have these excellent characteristics. 
     Patent Document 4 discloses a piezoelectric ceramic composition having a general formula of {(K 1-x Na x ) 1-y Ag y }NbO 3-z [M α     +   ][O 2− ] α     /2    (wherein 0≦x&lt;1, 0≦y≦0.1, 0≦z≦0.05, and 0&lt;y+z; M denotes at least one metallic element selected from the group consisting of Mn, Mg, In, Si, Ga, and Sb), and a is the average valence of a metallic element M). 
     According to Patent Document 4, the addition of predetermined amounts of Ag and at least one metallic element selected from the group consisting of Mn, Mg, In, Si, Ga, and Sb to (K, Na)NbO 3  can decrease the dielectric loss tan δ, improve the reliability, and increase the piezoelectric d constant. 
     [Patent Document 1 ] Japanese Unexamined Patent Application Publication No. 11-228227 
     [Patent Document 2 ] Japanese Unexamined Patent Application Publication No. 11-228228 
     [Patent Document 3 ] Japanese Unexamined Patent Application Publication No. 2004-244300 
     [Patent Document 4 ] Japanese Unexamined Patent Application Publication No. 2002-68835 
     DISCLOSURE OF INVENTION 
     Problems to be Solved by the Invention 
     While in Patent Documents 1 and 2 the addition of M1M2O 3  or M1M2M3O 3  to (K, Na, Li)(Nb, Ta)O 3  as a third component provides a relative dielectric constant ∈r as high as at least 1000, the increase in the content of the third component causes a decrease in the electromechanical coupling factor kp. Thus, the piezoelectric d constant increases slightly but insufficiently. 
     More specifically, the relationship among the piezoelectric d constant, the dielectric constant ∈ T , and the electrical coupling factor kp is expressed by a numerical formula (1): 
                   d   =     kp   ⁢         ɛ   T     Y                 (   1   )               
wherein Y denotes Young&#39;s modulus.
 
     Thus, it is desirable that both the relative dielectric constant ∈r and the electromechanical coupling factor kp are increased to yield a high piezoelectric d constant. However, although only the addition of M1M2O 3  or M3M4M2O 3  as a third component to (K, Na, Li)(Nb, Ta)O 3  as in Patent Documents 1 and 2, may increase the relative dielectric constant ∈r, the increase in the content of the third component causes a decrease in the electromechanical coupling factor kp. Thus, there is a problem that a desired sufficiently high piezoelectric d constant cannot be obtained. 
     Patent Document 3 describes that the addition of a metallic element, such as In, to {Li x (K 1-y Na y ) 1-x }(Nb 1-z-w Ta z Sb w )O 3  can reduce the percentage of open pores to 0.4% by volume or less. According to an experiment by the present inventors, it was found that the piezoelectric d constant was not increased remarkably, and a piezoelectric ceramic composition having a desired high piezoelectric d constant could not be obtained. 
     Patent Document 4 describes that the addition of Ag and, for example, In to (K, Na)NbO 3  increases d 31 . However, it was found that the increase was small and a piezoelectric ceramic composition having a sufficiently high piezoelectric d constant could not be obtained. 
     Furthermore, with the recent technical progress in the preparation of thinner ceramics, a high-field driven stacked piezoelectric ceramic electronic component has been developed and put to practical use. 
     It is desired that a piezoelectric material for a high electric field driven piezoelectric ceramic electronic component have a high piezoelectric d constant in the high electric field practically used. However, the piezoelectric d constant in a high electric field practically used is generally different from the piezoelectric d constant usually measured in a very low electric field. Thus, a high piezoelectric d constant in a very low electric field does not always mean there is a high piezoelectric d constant in a high electric field. 
     More specifically, a piezoelectric material includes a large number of regions exhibiting spontaneous polarization in different directions, called domains. In a very low electric field, the only responsive domain is 180° domains exhibiting spontaneous polarization parallel to the direction of the electric field applied. In a high electric field, in addition to the response of the 180° domains, 90° domains, which exhibit spontaneous polarization perpendicular to the direction of the electric field applied, turn toward the direction of the electric field applied, generating a large distortion. Thus, the piezoelectric d constant in a high electric field can be greater than that in a very low electric field. However, in a high electric field having a strength beyond a certain electric field strength where most of the 90° domains become 180° domains, a large displacement can no longer be achieved. The structure of a domain may vary with the composition of a piezoelectric material. Thus, even when a piezoelectric material has a high piezoelectric d constant in a very low electric field, the piezoelectric material may not have a high piezoelectric d constant in a high electric field in a manner that depends on the domain structure. 
     Studies by the present inventors showed that in known lead-free piezoelectric ceramic compositions as described in Patent Documents 1 to 4, the piezoelectric d constant in a very low electric field may be increased slightly but insufficiently, and the piezoelectric d constant in a high electric field is much smaller than the desired piezoelectric d constant. 
     The present invention was accomplished in light of such circumstances. Accordingly, it is an object of the present invention to provide a non-lead piezoelectric ceramic composition that can achieve desired high piezoelectric d constants in both a very low electric field and a high electric field and a piezoelectric ceramic electronic component produced using the piezoelectric ceramic composition. 
     Means for Solving the Problems 
     To achieve the object described above, the present inventors have conducted an intense study and found that a piezoelectric ceramic composition that contains a main component prepared by dissolving M1 0.5 Bi 0.5 M2O 3  (wherein M1 is K or Na, and M2 is Ti, Zr or Sn) having a perovskite structure as a component in a (K, Na, Li)(Nb, Ta, Sb)O 3 -based compound having a predetermined molar ratio and another perovskite structure, and also contains about 0.1 to 10 mol in total of at least one specific element selected from the group consisting of In, Sc, Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu per 100 mol of the main component can have an increased relative dielectric constant ∈r, an increased electromechanical coupling factor kp, a high Curie point Tc, and the desired high piezoelectric d constants in both a very low electric field and a high electric field. 
     The present invention was achieved on the basis of such findings. A piezoelectric ceramic composition according to the present invention contains a main component having a general formula of {(1−x)(K 1-a-b Na a Li b ) m (Nb 1-c-d Ta c Sb d )O 3 -x(M1 0.5 Bi 0.5 ) n M2O 3 } (wherein M1 is at least one metallic element selected from the group consisting of K and Na, M2 is at least one metallic element selected from the group consisting of Ti, Zr and Sn, and x, a, b, c, d, m and n are in the ranges of 0.005≦x≦0.5, 0≦a≦0.9, 0≦b≦0.3, 0≦a+b≦0.9, 0≦c≦0.5, 0≦d≦0.1, 0.9≦m≦1.1, and 0.9≦n≦1.1, respectively), and about 0.1 to 10 mol in total of at least one specific element selected from the group consisting of In, Sc, Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu per 100 mols of the main component. 
     It was also found that when the piezoelectric ceramic composition is prepared to have the molar ratio m of (K 1-a-b Na a Li b ) and (Nb 1-c-d Ta c Sb d ) in the range of 0.9≦m≦0.99, the piezoelectric d constant in a high electric field can be improved further efficiently. 
     Thus, the m is preferably in the range of 0.9≦m≦0.99 in a piezoelectric ceramic composition according to the present invention. 
     A known piezoelectric ceramic composition containing (K, Na)NbO 3  as a main component has a very narrow firing temperature range for preparing a satisfactory sintered compact. Practically, this causes a serious problem in mass production. Thus, it is desired that a satisfactory sintered compact can be prepared in a wider firing temperature range. 
     The present inventors have conducted an intense study and found that when a piezoelectric ceramic composition is prepared to contain about 1.5 to 10 mol in total of the specific element described above per 100 mol of the main component, the temperature range ΔT under which stable firing can be performed can be increased. Thus, fluctuations in the firing temperature during sintering have a smaller effect. This can reduce the number of defectives and thus increase productivity. 
     Thus, a piezoelectric ceramic composition according to the present invention preferably contains about 1.5 to 10 mol in total of the specific element per 100 mols of the main component. 
     In addition, it was found that the presence of about 0.1 to 10 mol in total of at least one metallic element selected from the group consisting of Mn, Ni, Fe, Zn, Cu and Mg per 100 mols of the main component can further increase the firing temperature range ΔT. 
     Thus, the piezoelectric ceramic composition according to the present invention may further contain about 0.1 to 10 mol in total of at least one metallic element selected from the group consisting of Mn, Ni, Fe, Zn, Cu and Mg per 100 mols of the main component. 
     A piezoelectric ceramic electronic component according to the present invention includes an external electrode disposed on a surface of a piezoelectric ceramic element, wherein the piezoelectric ceramic element is formed of the piezoelectric ceramic composition described above. 
     Furthermore, the piezoelectric ceramic element may include an internal electrode in the piezoelectric ceramic electronic component according to the present invention. 
     Advantages of the Invention 
     A piezoelectric ceramic composition according to the present invention contains a main component having a general formula of {(1−x)(K 1-a-b Na a Li b ) m (Nb 1-c-d Ta c Sb d )O 3-X (M1 0.5 Bi 0.5 ) n M2O 3 } (wherein M1 is at least one metallic element selected from the group consisting of K and Na, M2 is at least one metallic element selected from the group consisting of Ti, Zr and Sn, and x, a, b, c, d, m and n are in the ranges of 0.005≦x≦0.5, 0≦a≦0.9, 0≦b≦0.3, 0≦a+b≦0.9, 0≦c≦0.5, 0≦d≦0.1, 0.9≦m≦1.1, and 0.9≦n≦1.1, respectively, and about 0.1 to 10 mol in total of at least one specific element selected from the group consisting of In, Sc, Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu per 100 mols of the main component. Thus, the piezoelectric d constant can be increased in both a very low electric field and a high electric field. Specifically, a piezoelectric ceramic composition thus produced can have excellent piezoelectric characteristics: the piezoelectric d 33  constant in a very low electric field is at least 105 pC/N and the piezoelectric d constant in a high electric field is at least 150 pC/N. 
     Furthermore, a piezoelectric ceramic composition according to the present invention can have further improved piezoelectric characteristics when the m is in the range of 0.9≦m≦0.99. Specifically, a piezoelectric ceramic composition thus produced can have a piezoelectric d 33  constant in a very low electric field of at least 110 pC/N and the piezoelectric d constant in a high electric field of at least 180 pC/N. 
     Preferably, a piezoelectric ceramic composition according to the present invention contains about 1.5 to 10 mol in total of the specific element per 100 mol of the main component. This can increase the temperature range ΔT for stable firing and reduce the number of defectives even in the presence of fluctuations in the firing temperature. Specifically, the temperature range ΔT can be at least about 20 degrees C. Thus, the productivity can be improved. 
     Preferably, a piezoelectric ceramic composition according to the present invention further contains about 0.1 to 10 mol in total of at least one metallic element selected from the group consisting of Mn, Ni, Fe, Zn, Cu and Mg per 100 mols of the main component. This can further increase the firing temperature range ΔT. Specifically, the addition of the bivalent metallic element described above can further increase the firing temperature range ΔT by about 10 to about 25 degrees C. Thus, the temperature range ΔT can be increased by about 45 to about 60 degrees C. in total. 
     A piezoelectric ceramic electronic component according to the present invention includes an external electrode disposed on a surface of a piezoelectric ceramic element, wherein the piezoelectric ceramic element is formed of the piezoelectric ceramic composition described above. Thus, a piezoelectric ceramic electronic component having a high piezoelectric constant in not only a very low electric field but also a high electric field can consistently be produced. 
     A piezoelectric ceramic electronic component according to the present invention may have a piezoelectric ceramic element including an internal electrode. Thus, even a high-field driven stacked piezoelectric ceramic electronic component, such as a piezoelectric actuator, can have a high piezoelectric d constant at a driving electric field. Thus, a piezoelectric ceramic electronic component having excellent piezoelectric characteristics can be produced in a consistent and highly efficient manner. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic single view drawing of a perovskite oxygen octahedral structure. 
         FIG. 2  is a cross-sectional view of a stacked piezoelectric actuator as a piezoelectric ceramic electronic component according to one embodiment of the present invention. 
     
    
    
     REFERENCE NUMERALS 
       1  piezoelectric ceramic element 
       2   a ,  2   b  external electrode 
       3  internal electrode 
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The present invention will be further illustrated with embodiments below. 
     A piezoelectric ceramic composition according to one embodiment (first embodiment) of the present invention is expressed by a general formula (A):
 
100{(1- x )(K 1-a-b Na a Li b ) m (Nb 1-c-d Ta c Sb d )O 3-X ( M 1 0.5 Bi 0.5 ) n   M 2O 3 }+(α/2)X 2 O 3    (A)
 
     wherein M1 is at least one metallic element selected from the group consisting of K and Na, M2 is at least one metallic element selected from the group consisting of Ti, Zr and Sn, and X is at least one specific element selected from the group consisting of In, Sc, Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu. 
     The α, x, a, b, c, d, m and n satisfy numerical formulas (2) to (10):
 
0.1≦α≦10   (2)
 
0.005≦x≦0.5   (3)
 
0≦a≦0.9   (4)
 
0≦b≦0.3   (5)
 
0 ≦a+b≦ 0.9   (6)
 
0≦c≦0.5   (7)
 
0≦d≦0.1   (8)
 
0.9≦m≦1.1   (9)
 
0.9≦n≦1.1   (10)
 
     Thus, the piezoelectric ceramic composition contains a main component {(K 1-a-b Na a Li b ) m (Nb 1-c-d Ta c Sb d )O 3 -(M1 0.5 Bi 0.5 ) n M2O 3 } of a perovskite structure (general formula ABO 3 ) prepared to have a predetermined molar ratio and about 0.1 to 10 mol of a specific element X, such as In or Sc, per 100 mols of the main component. The piezoelectric ceramic composition can have high piezoelectric d constants in both a very low electric field and a high electric field and desired piezoelectric characteristics. 
     In other words, as described in Background Art, a solid solution of a perovskite complex oxide component having a specific composition dissolved as a third component in (K, Na, Li)(Nb, Ta)O 3  can have a high piezoelectric d constant. However, a simple solid solution of a perovskite complex oxide component having a specific composition only dissolved in (K, Na, Li)(Nb, Ta)O 3  cannot have a sufficiently high piezoelectric d constant (for example, at least 100 pC/N). The simple solid solution has piezoelectric characteristics inferior to those of a lead-based piezoelectric ceramic composition particularly in a high electric field. 
     As illustrated in  FIG. 1 , a perovskite structure has a B site ion-centered oxygen octahedral skeleton and an A site ion coordinating in the skeletal space. In  FIG. 1 , P represents an oxygen octahedral skeleton, a black sphere represents a B site ion, a hatched sphere represents an A site ion, and a white sphere represents an O 2−  ion. 
     In (K, Na)NbO 3 , for example, the A site ions K + and Na + coordinate in a B site ion Nb 5+ -centered oxygen octahedral skeleton. In (Na 0.5 Bi 0.5 ) n TiO 3 , A site ions Na + and Bi 3+ coordinate in a B site ion Ti 4+ -centered oxygen octahedral skeleton. 
     To prepare a uniform solid solution of complex oxides of different compositions having the perovskite structure, their B site ion-centered oxygen octahedral structures must naturally be commensurate with each other. 
     When the valencies of B site ions are identical as in (K, Na)NbO 3  and LiSbO 3 , the B site ions Nb 5+  and Sb 5+ blend with each other relatively freely. Thus, a totally uniform oxygen octahedral skeleton can be formed in a solid solution of these, and their B site ion-centered oxygen octahedral structures can be commensurate with each other. 
     However, when a solid solution is prepared from perovskite complex oxides having different B site ion valencies, such as (K, Na)NbO 3  and (Na 0.5 Bi 0.5 ) n TiO 3 , only Nb 5+  ions dissolve in the surroundings of a K +  ion and only Ti 4+  ions dissolve in the surroundings of a Bi 3+  ion to maintain the balance of local charges. Thus, the Nb 5+  ions and the Ti 4+  ions cannot blend with each other freely and form oxygen octahedral structures having different sizes. In this case, the oxygen octahedral structures between the perovskite complex oxides commensurate poorly with each other. This makes it difficult to prepare an excellent piezoelectric ceramic composition, compromising the piezoelectricity. 
     In the present embodiment, the addition of a predetermined mol of a specific element, such as In or Sc, to the main component allows oxygen octahedral structures of different perovskite complex oxides to be commensurate with each other, providing high piezoelectric d constants in both a very low electric field and a high electric field. 
     More specifically, when In, for example, in an oxide form is added as a specific element in addition to (K 0.5 Na 0.5 )NbO 3  and (Na 0.5 Bi 0.5 ) n TiO 3 , as shown in reaction formula (B), part of In replaces part of K and Na in (K 0.5 Na 0.5 )NbO 3  and part of Ti in (Na 0.5 Bi 0.5 ) n TiO 3 . Furthermore, In acts to maintain the total balance of charges and blends with part of Nb and Ti.
 
100{(1− x )(K 0.5 Na 0.5 )NbO 3   +x (Na 0.5 Bi 0.5 ) n TiO 3 }+(α/2)In 2 O 3 →100{(1− x− (α/200))(K 0.5 Na 0.5 )NbO 3 −( x−α/ 100))(Na 0.5 Bi 0.5 ) n TiO 3 −(α/100)(K 0.25 Na 0.25 In 0.5 )TiO 3 −(α/100)(Na 0.5 Bi 0.5 )(In 0.5 Nb 0.5 )O 3 }  (B)
 
     Since In 3+  ions blend with A site ions and B site ions, the mixed layer reduces mismatching between different perovskite complex oxides to be naturally commensurate with each other, thus forming a matching layer. The presence of a matched layer of {(α/100)(K 0.25 Na 0.25 In 0.5 )TiO 3 −(α/100)(Na 0.5 Bi 0.5 )(In 0.5 )O 3 } can provide a sufficiently high piezoelectric d constant even in a very low electric field. Since the matching layer is believed to form a domain wall, a large number of small domains are expected to be formed, as compared with a solid solution of perovskite complex oxides having the same valency of B site ions. Each of the large number of small domains expand, contract, and rotate in a high electric field to generate large deformation and distortion in total. This achieves a much higher piezoelectric d constant in a high electric field than that of a solid solution of perovskites having the same valency of B site ions. This may provide a piezoelectric ceramic composition having excellent piezoelectric characteristics and a high piezoelectric d constant in not only a very low electric field but also a high electric field. 
     The specific element X is limited to at least one element selected from the group consisting of In, Sc, Y, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb and Lu. Although all the specific elements X described above are trivalent metallic elements, it does not mean that any trivalent metallic element can be used. For example, Bi or La is not appropriate as an additive element. Thus, the specific element X is limited to the metallic elements described above. 
     Then, reasons that α, x, a, b, c, d, m and n are limited to the ranges of the numerical formulas (2) to (10) are described in detail below. 
     (1) α 
     The addition of a specific element, such as In, can increase the piezoelectric d constants in both a very low electric field and a high electric field. To this end, the number of moles a of the specific element X should be at least about 0.1 mol per 100 mols of the main component. However, when the number of moles a of the specific element X is more than about 10 mol per 100 mols of the main component, the content of the specific element X exceeds the solubility limit. The specific element X that cannot be dissolved in a solid solution may be precipitated on the grain boundary to form a conductive layer, causing poor polarization. 
     Thus, a piezoelectric ceramic composition is prepared to have the number of moles α of the specific element X per 100 mol of the main component in the range of in the present embodiment, 0.1≦α≦10 in the present embodiment. 
     When the number of moles a is in the range of 1.5≦α≦10, the temperature range ΔT for stable firing can be increased. 
     In a known piezoelectric ceramic composition, the temperature range ΔT for stable firing is very narrow. Fluctuations in the firing temperature may increase the occurrence of defectives and decrease the productivity. 
     The present inventors found that the number of moles α of the specific element X in the range of 1.5≦α≦10 per 100 mol of a main component allows the temperature range ΔT for stable firing to be increased. This allows a margin for fluctuations in the firing temperature; a little fluctuation in the firing temperature is not detrimental to sintering. Thus, a piezoelectric ceramic composition having excellent piezoelectric characteristics can be produced in a consistent and highly efficient manner. Specifically, the firing temperature range ΔT can be at least 20 degrees C. Thus, the number of moles a of the specific element X is preferably in the range of 1.5≦α≦10 per 100 mol of the main component. 
     (2) x 
     x defines the molar ratio of a third component (M1 0.5 Bi 0.5 ) n M2O 3  in a main component. When x is less than 0.005, the content of (M1 0.5 Bi 0.5 ) n M2O 3  is too low. This decreases the relative dielectric constant ∈r and the electromechanical coupling factor kp. Thus, a desired high piezoelectric d constant cannot be achieved, and the piezoelectric characteristics cannot be improved. When x is more than 0.5, the Curie point Tc decreases remarkably and the electromechanical coupling factor kp decreases rapidly and the piezoelectric characteristics become deteriorated. 
     Thus, components of a composition in the present embodiment are prepared so that x is in the range of 0.005≦x≦0.5. 
     (3) a, b 
     Na and Li are contained in a main component if necessary. Na and Li replace part of K in a solid solution. When a, which defines the molar ratio of Na, exceeds 0.9, a ferroelectric cannot be formed. When b, which defines the molar ratio of Li, exceeds 0.3, the amount of Li exceeds the solubility limit with K. Both cases result in lack of piezoelectricity. Furthermore, when the total of a and b exceeds 0.9, the relative dielectric constant ∈r decreases remarkably. Thus, a desired high piezoelectric d constant cannot be achieved. 
     Thus, components of a composition in the present embodiment are prepared so that a and b are in the ranges of 0≦a≦0.9, 0≦b≦0.3, and 0≦a+b≦0.9. 
     (4) c 
     Ta is also contained in a main component if necessary. Ta replaces part of Nb in a solid solution. When c, which defines the molar ratio of Ta, exceeds 0.5, the electromechanical coupling factor kp decreases greatly, the piezoelectric d constants in both a very low electric field and a high electric field decrease remarkably, and thus desired piezoelectric characteristics cannot be obtained. 
     Thus, components of a composition in the present embodiment are prepared so that c is in the range of 0≦c≦0.5. 
     (5) d 
     Sb is contained in a main component if necessary. Sb replace part of Nb in a solid solution. When d, which defines the molar ratio of Sb, exceeds 0.1, the Curie point Tc decreases remarkably. This results in lack of piezoelectricity. 
     Thus, components of a composition in the present embodiment are prepared so that d is in the range of 0≦d≦0.1. 
     (6) m 
     m defines the molar ratio of A sites and B sites in (K 1-a-b Na a Li b ) m (Nb 1-c-d Ta c Sb d )O 3 . When m is less than 0.9, the molar ratio of an A site is too small. This greatly decreases the electromechanical coupling factor kp and remarkably decreases the piezoelectric d constants in both a very low electric field and a high electric field. Thus, desired piezoelectric characteristics cannot be obtained. When m exceeds 1.1, the molar ratio of an A site becomes excessive. This causes poor sintering. 
     Thus, components of a composition in the present embodiment are prepared so that m is in the range of 0.9≦m≦1.1. Preferably, m is in the range of 0.9≦m≦0.99 to achieve a higher piezoelectric d constant. 
     (7) n 
     n defines the molar ratio of A sites and B sites in (M1 0.5 Bi 0.5 ) n M2O 3 . When n is less than 0.9 or more than 1.1, the electromechanical coupling factor kp decreases greatly, and the piezoelectric d constants in both a very low electric field and a high electric field decrease remarkably. Thus, desired piezoelectric characteristics cannot be obtained. When n exceeds 1.1, the molar ratio of an A site becomes excessive. This causes poor sintering. 
     Thus, components of a composition in the present embodiment are prepared so that n is in the range of 0.9≦n≦1.1. 
     In the present embodiment, a piezoelectric ceramic composition having the general formula (A) is prepared to satisfy the numerical formulas (2) to (10). This can provide a piezoelectric ceramic composition having high piezoelectric d constants in both a very low electric field and a high electric field and excellent piezoelectric characteristics. 
     Furthermore, a piezoelectric ceramic composition is prepared so that the number of moles α of the specific element X is in the range of 1.5≦α≦10 per 100 mol of a main component. Thus, the temperature range ΔT for stable firing can be increased. This allows a piezoelectric ceramic composition having a desired piezoelectric d constant and excellent piezoelectric characteristics to be produced in a consistent and highly efficient manner. Thus, the productivity can be improved. 
     The present invention is not limited to the piezoelectric ceramic composition according to the embodiment described above. It is also preferred to add in the present embodiment, 0.1 to 10 mol of at least one element selected from the group consisting of Mn, Ni, Fe, Zn, Cu and Mg to 100 mols of a main component composed of a solid solution in a general formula (A). This can further increase the firing temperature range ΔT and further improve the productivity (second embodiment). 
     In this case, a piezoelectric ceramic composition can be expressed by a general formula (C):
 
100{(1− x−y )(K 1-a-b Na a Li b ) m (Nb 1-c-d Ta c Sb b )O 3-X ( M 1 0.5 Bi 0.5 ) n   M 2O 3 }(α/2)X 2 O 3 +β[Z q+ ][O 2− ] (q/2)    (C)
 
wherein Z is at least one metallic element selected from the group consisting of Mn, Ni, Fe, Zn, Cu and Mg.
 
     The reason that the addition of Mn, Ni, Fe, Zn, Cu or Mg to the main component can increase the firing temperature range ΔT is thought to be that the element dissolved in a crystal grain serves to compensate for the charge and facilitates the formation of a matching layer and thereby improves sintering. 
     The reason that the additive level is in the present embodiment, 0.1 to 10 mol per 100 mols of the main component is that at least in the present embodiment, 0.1 mol per 100 mol of a main component is required to further increase the firing temperature range ΔT, and that the additive level of more than in the present embodiment, 10 mol may cause poor sintering. 
     Thus, when Mn, Ni, Fe, Zn, Cu or Mg is added to a main component, the preparation should be performed so that its content is in the present embodiment, 0.1 to 10 mol per 100 mols of the main component. 
     A piezoelectric ceramic electronic component produced using the piezoelectric ceramic composition described above is described below. 
       FIG. 2  is a cross-sectional view of a stacked piezoelectric actuator as a piezoelectric ceramic electronic component according to one embodiment of the present invention. The stacked piezoelectric actuator includes a piezoelectric ceramic element  1 , external electrodes  2  ( 2   a  and  2   b ) formed on both ends of the piezoelectric ceramic element  1  and composed of an electrical conductivity material, such as Ag, and internal electrodes  3  ( 3   a  to  3   g ) included in parallel with each other in the opposite direction in the piezoelectric ceramic element  1  and composed of an electrical conductive material, such as Ag or Ag—Pd. 
     In the stacked piezoelectric actuator, one end of each of the internal electrodes  3   a ,  3   c ,  3   e , and  3   g  is electrically connected to one external electrode  2   a , and one end of each of the internal electrodes  3   b ,  3   d , and  3   f  is electrically connected to the other external electrode  2   b . When a voltage is applied between the external electrode  2   a  and the external electrode  2   b , the stacked piezoelectric actuator shifts in a stacked direction indicated by an arrow X because of a longitudinal piezoelectric effect. 
     A method for manufacturing the stacked piezoelectric actuator is described in detail below. 
     Predetermined amounts of at least one compound selected from the group consisting of TiO 2 , ZrO 2  and SnO 2 ; at least one compound selected from the group consisting of In 2 O 3 , Sc 2 O 3 , Y 2 O 3 , Nd 2 O 3 , Sm 2 O 3 , Eu 2 O 3 , Gd 2 O 3 , Tb 4 O 7 , Dy 2 O 3 , HO 2 O 3 , Er 2 O 3 , Yb 2 O 3  and Lu 2 O 3 ; K 2 CO 3 ; Nb 2 O 5 ; Bi 2 O 3 ; Na 2 CO 3 , Li 2 CO 3  if necessary; and at least one compound selected from the group consisting of MnCO 3 , NiO, Fe 2 O 3 , ZnO, CuO and MgCO 3  if necessary are weighed as raw materials for a ceramic. The weighed raw materials are charged in a ball mill containing grinding media, such as zirconia, are wet-blended sufficiently, and are dried to yield a ceramic raw powder. 
     Subsequently, the ceramic raw powder is calcined at a predetermined temperature (for example, 600 to 1000 degrees C.). The calcined powder is again wet-ground in a ball mill to produce a raw powder before sintering. 
     Then, the raw powder before sintering and an organic binder are wet-blended to form a slurry. Subsequently, a ceramic green sheet is produced, for example, by a doctor blade method. 
     Then, an electrical conductive paste containing a main component of Ag or Ag—Pd for an internal electrode is used to screen-print the ceramic green sheet, thus forming an electrode pattern. 
     Then, the ceramic green sheets on which the electrode pattern is screen-printed are stacked and are subsequently sandwiched between ceramic green sheets on which no electrode pattern is screen-printed. These ceramic green sheets are attached by pressure to form a stacked body. Then, the stacked body is cut into pieces having a predetermined size. The pieces are placed in an alumina case and are calcined at a predetermined temperature (for example, 250 to 500 degrees C.) to remove the binder. Then, the pieces are fired at a predetermined temperature (for example, 1050 to 1200 degrees C.) to form a piezoelectric ceramic element including internal electrodes therein. 
     Subsequently, an electrical conductive paste, for example, containing Ag for an external electrode is applied to both ends of the piezoelectric ceramic element, and is baked at a predetermined temperature (for example, 750 to 850 degrees C.) to form external electrodes  2   a  and  2   b . Then, prescribed poling is performed to produce a stacked piezoelectric actuator. It is essential only that the external electrodes  2   a  and  2   b  have satisfactory adhesiveness. Thus, the external electrodes  2   a  and  2   b  may be formed by a thin-film forming method, for example, sputtering or vacuum evaporation. 
     In the present embodiment, a stacked piezoelectric actuator is produced using a piezoelectric ceramic composition according to the present invention. Even when a high electric field of 1 kV/mm is applied, the piezoelectric actuator can have a large piezoelectric d constant and exhibit a large displacement. 
     The present invention is not limited to the embodiments described above. In those embodiments, a stacked piezoelectric actuator is described as a piezoelectric ceramic electronic component. The present invention can also be applied to a single-plate piezoelectric actuator and a bimorph piezoelectric actuator. Furthermore, it is needless to say that the piezoelectric ceramic composition can be used in various piezoelectric ceramic electronic components, such as a piezoelectric resonator, a piezoelectric buzzer, and a piezoelectric sensor. 
     Then, the present invention will be specifically described with Examples below. 
     EXAMPLE 1 
     K 2 CO 3 , Na 2 CO 3 , Nb 2 O 5 , Bi 2 O 3 , TiO 2 , ZrO 2 , SnO 2 , In 2 O 3 , Sc 2 O 3 , Yb 2 O 3 , Y 2 O 3 , Nd 2 O 3 , Eu 2 O 3 , Gd 2 O 3 , Dy 2 O 3 , Sm 2 O 3 , HO 2 O 3 , Er 2 O 3 , Tb 4 O 7  and Lu 2 O 3  were prepared as raw materials for ceramics. 
     These raw materials for ceramics were weighed to prepare compositions shown in Table 1. The weighed raw materials were wet-blended in alcohol in a ball mill for 18 hours. Each of the resulting mixtures was dried and calcined at 700 to 1000 degrees C. 
     Then, the calcined mixture was roughly ground. The ground mixture and a proper amount of an organic binder were wet-ground in a ball mill for 16 hours and sifted through a 40-mesh sieve to control the particle size. 
     Then, the powder having a controlled particle size was pressed at a pressure of 9.8×10 7  to 1.96×10 8  Pa into a discoidal compact having a diameter of 10 mm and a thickness of 1.2 mm. The compact was fired at a temperature of 1050 to 1200 degrees C. in the air for two hours to produce a ceramic element. 
     A compact was fired for two hours every five degree C. between 1050 and 1200 degrees C. The piezoelectric d 33  constant at each firing temperature was measured with a d 33  meter. The firing temperature at a maximum piezoelectric d 33  constant was considered as an optimum firing temperature. A firing temperature range in which at least 80% of the maximum piezoelectric d 33  constant can be achieved was considered as the firing temperature range ΔT for stable firing. 
     Then, Ag electrodes were formed on both main surfaces of the ceramic element by vacuum evaporation. Subsequently, the ceramic element was polarized in an isolating oil at a bath temperature of 20 to 180 degrees C. by applying a 2 to 10 kV/mm direct-current voltage for 10 to 30 minutes. Thus, compositions of sample numbers 1 to 27 having a general formula of 100{(1−x)(K 0.5 Na 0.5 ) 0.98 NbO 3-X (M1 0.5 Bi 0.5 ) n M2O 3 }+(α/2)X 2 O 3  were prepared. 
     Table 1 illustrates the compositions of sample numbers 1 to 27. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
             
            
               
                   
                   
               
               
                   
                   
                 Composition: 
               
               
                   
                   
                 100{(1 − x)(K 0.5 Na 0.5 ) 0.98 NbO 3  − 
               
               
                   
                 Sample 
                 x(M1 0.5 Bi 0.5 )M2O 3 } + (α/2)X 2 O 3   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 No. 
                 x 
                 M1 
                 M2 
                 X 
                 α 
               
               
                   
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                  1 
                 0.05 
                 Na 
                 Ti 
                 In 
                 2 
               
               
                   
                  2 
                 0.05 
                 Na 
                 Ti 
                 Sc 
                 2 
               
               
                   
                  3 
                 0.05 
                 Na 
                 Ti 
                 Yb 
                 2 
               
               
                   
                  4 
                 0.05 
                 Na 
                 Ti 
                 Y 
                 2 
               
               
                   
                  5 
                 0.05 
                 Na 
                 Ti 
                 Nd 
                 2 
               
               
                   
                  6 
                 0.05 
                 Na 
                 Ti 
                 Eu 
                 2 
               
               
                   
                  7 
                 0.05 
                 Na 
                 Ti 
                 Gd 
                 2 
               
               
                   
                  8 
                 0.05 
                 Na 
                 Ti 
                 Dy 
                 2 
               
               
                   
                  9 
                 0.05 
                 Na 
                 Ti 
                 Sm 
                 2 
               
               
                   
                 10 
                 0.05 
                 Na 
                 Ti 
                 Ho 
                 2 
               
               
                   
                 11 
                 0.05 
                 Na 
                 Ti 
                 Er 
                 2 
               
               
                   
                 12 
                 0.05 
                 Na 
                 Ti 
                 Tb 
                 2 
               
               
                   
                 13 
                 0.05 
                 Na 
                 Ti 
                 Lu 
                 2 
               
               
                   
                 14 
                 0.05 
                 Na 
                 Ti 
                 Yb/In 
                 1/1 
               
               
                   
                 15 
                 0.05 
                 Na 
                 Ti 
                 Y/In 
                 1/1 
               
               
                   
                  16* 
                 0.05 
                 Na 
                 Ti 
                 Bi 
                 2 
               
               
                   
                  17* 
                 0.05 
                 Na 
                 Ti 
                 La 
                 2 
               
               
                   
                  18* 
                 0.05 
                 Na 
                 Ti 
                 — 
                 — 
               
               
                   
                 19 
                 0.05 
                 Na 
                 Ti 
                 In 
                 0.1 
               
               
                   
                 20 
                 0.05 
                 Na 
                 Ti 
                 In 
                 1 
               
               
                   
                 21 
                 0.05 
                 Na 
                 Ti 
                 In 
                 1.5 
               
               
                   
                 22 
                 0.05 
                 Na 
                 Ti 
                 In 
                 10 
               
               
                   
                  23* 
                 0.05 
                 Na 
                 Ti 
                 In 
                 15 
               
               
                   
                 24 
                 0.05 
                 Na 
                 Zr 
                 In 
                 2 
               
               
                   
                 25 
                 0.05 
                 Na 
                 Sn 
                 In 
                 2 
               
               
                   
                 26 
                 0.05 
                 K 
                 Ti 
                 In 
                 2 
               
               
                   
                 27 
                 — 
                 — 
                 — 
                 In 
                 2 
               
               
                   
                   
               
               
                   
                 *means outside of the scope of the present invention. 
               
            
           
         
       
     
     In the sample numbers 1 to 27, the relative dielectric constant ∈r, the electromechanical coupling factor kp, the piezoelectric d 33  constant in a very low electric field (hereinafter referred to simply as “piezoelectric d 33  constant”), the piezoelectric d 33  constant measured in a high electric field (hereinafter referred to as “piezoelectric d 33  constant in a high electric field”), and the Curie point Tc were measured. 
     The relative dielectric constant ∈r was determined from the capacitance measured with an impedance analyzer and the sample size. The electromechanical coupling factor kp was determined by a resonance-antiresonance method using an impedance analyzer. 
     The piezoelectric d 33  constant was determined with a d 33  meter from the amount of electric charge generated under oscillation corresponding to the application of an electric field of about 1 V/mm. 
     The piezoelectric d 33  constant in a high electric field was calculated by measuring the displacement in the thickness direction in an electric field of 1 kV/mm in the thickness direction with a displacement gage, calculating the distortion factor by dividing the displacement by the thickness, and dividing the distortion factor by the electric field. 
     The Curie point Tc was determined by analyzing a temperature characteristic of the relative dielectric constant Er and calculating the temperature at a maximum relative dielectric constant ∈r. 
     Table 2 gives the measurements and the firing temperature ranges ΔT for sample numbers 1 to 27. 
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                   
                   
                   
                   
                 Piezoelectric d 33   
                   
                   
               
               
                   
                 Relative 
                 Electromechanical 
                 Piezoelectric d 33   
                 constant in a high 
                   
                 Firing temperature 
               
               
                 Sample 
                 dielectric 
                 coupling factor kp 
                 constant 
                 electric field 
                 Curie point Tc 
                 range ΔT 
               
               
                 No. 
                 constant εr 
                 (%) 
                 (pC/N) 
                 (pC/N) 
                 (° C.) 
                 (° C.) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                  1 
                 790 
                 50.1 
                 242 
                 393 
                 310 
                 35 
               
               
                  2 
                 765 
                 47.3 
                 221 
                 364 
                 310 
                 35 
               
               
                  3 
                 810 
                 37.2 
                 165 
                 274 
                 290 
                 35 
               
               
                  4 
                 910 
                 31.6 
                 157 
                 261 
                 280 
                 35 
               
               
                  5 
                 890 
                 27.0 
                 130 
                 218 
                 290 
                 25 
               
               
                  6 
                 896 
                 29.4 
                 143 
                 239 
                 290 
                 25 
               
               
                  7 
                 810 
                 29.2 
                 133 
                 223 
                 300 
                 25 
               
               
                  8 
                 863 
                 32.2 
                 146 
                 244 
                 290 
                 35 
               
               
                  9 
                 846 
                 35.4 
                 165 
                 274 
                 290 
                 35 
               
               
                 10 
                 736 
                 33.6 
                 142 
                 237 
                 300 
                 35 
               
               
                 11 
                 856 
                 35.2 
                 165 
                 274 
                 290 
                 35 
               
               
                 12 
                 860 
                 27.2 
                 121 
                 210 
                 290 
                 35 
               
               
                 13 
                 765 
                 47.2 
                 225 
                 370 
                 310 
                 35 
               
               
                 14 
                 854 
                 49.5 
                 237 
                 385 
                 300 
                 40 
               
               
                 15 
                 843 
                 48.7 
                 233 
                 383 
                 300 
                 40 
               
               
                  16* 
                 654 
                 13.5 
                 63 
                 93 
                 260 
                 Low reproducibility 
               
               
                  17* 
                 573 
                 11.8 
                 52 
                 74 
                 270 
                 Fraction defective 
               
               
                  18* 
                 623 
                 15.4 
                 64 
                 90 
                 310 
                 ≧95% 
               
               
                 19 
                 763 
                 24.3 
                 112 
                 182 
                 310 
                 5 
               
               
                 20 
                 772 
                 24.8 
                 114 
                 186 
                 310 
                 10 
               
               
                 21 
                 788 
                 48.3 
                 231 
                 381 
                 310 
                 30 
               
               
                 22 
                 782 
                 49.5 
                 230 
                 376 
                 310 
                 30 
               
            
           
           
               
               
            
               
                  23* 
                 No piezoelectricity 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 24 
                 675 
                 46.3 
                 201 
                 332 
                 310 
                 40 
               
               
                 25 
                 576 
                 44.2 
                 182 
                 301 
                 310 
                 40 
               
               
                 26 
                 593 
                 44.3 
                 183 
                 303 
                 310 
                 35 
               
               
                 27 
                 380 
                 30.1 
                 93 
                 124 
                 400 
                 20 
               
               
                   
               
               
                 *means outside of the scope of the present invention. 
               
            
           
         
       
     
     Sample numbers 1 to 17 contain a total of 2 mols of trivalent metallic elements per 100 mols of main component having a composition formula of {0.95 (K 0.5 Na 0.5 ) 0.98 NbO 3 -0.05(Na 0.5 Bi 0.5 )TiO 3 }. 
     Sample numbers 1 to 15 contain a specific element (In, Sc, Yb, Y, Nd, Eu, Gd, Dy, Sm, Ho, Er, Tb and Lu) according to the present invention. Thus, they have a high relative dielectric constant Er and a high electromechanical coupling factor kp. As a result, sample numbers 1 to 15 have piezoelectric d 33  constants of at least 105 pC/N and piezoelectric d 33  constants in a high electric field of at least 150 pC/N, and thus exhibit excellent piezoelectric characteristics. 
     Furthermore, it was found that when the number of moles α of each metallic element was 2 mol per 100 mol of a main component and was in the range of 1.5 to 10 mol, the temperature range ΔT for stable firing could be increased to 25 to 40 degrees C. 
     By contrast, sample numbers 16 and 17 contained Bi or La as a trivalent metallic element (i.e., other than the specific element) and had very low electromechanical coupling factors kp. Thus, sample numbers 16 and 17 had low piezoelectric d 33  constants and low piezoelectric d 33  constants in a high electric field, and did not have the desired piezoelectric characteristics. Furthermore, the firing temperature fluctuated. This resulted in poor reproducibility even when firing was performed at the same temperature. The fraction of defectives was at least 95%. This is probably because Bi or La cannot dissolve in the B site of BaTiO 3 , and a matched layer between (K 0.5 Na 0.5 )NbO 3  and (Na 0.5 Bi 0.5 )TiO 3  could not consistently be formed. 
     Sample number 18 did not contain an additive element in the main component. As in sample numbers 16 and 17, sample number 18 had a very low electromechanical coupling factor kp. As a result, sample number 18 had a low piezoelectric d 33  constant and a low piezoelectric d 33  constant in a high electric field, and did not have desired piezoelectric characteristics. Furthermore, the firing temperature fluctuated. This resulted in poor reproducibility even when firing was performed at the same temperature. The fraction of defectives was at least 95%. 
     These results showed that it is important to add the specific element within the scope of the present invention to a main component to improve the piezoelectric characteristics. 
     Sample numbers 19 to 23 contain different molar amounts of In for a main component having a composition formula of {0.95(K 0.5 Na 0.5 ) 0.98 NbO 3 -0.05(Na 0.5 Bi 0.5 )TiO 3 }. 
     Sample number 23 was poorly polarized and did not exhibit piezoelectricity. This is probably because the molar amount of In was am excessive 15 mols per 100 mols of the main component, and In undissolved in the main component was deposited on a grain boundary and formed a conductive layer. 
     By contrast, it was found that when 0.1 to 10 mol of In was added to 100 mol of a main component, in sample numbers 19 to 22, that the piezoelectric d 33  constants were at least 105 pC/N, the piezoelectric d 33  constants in a high electric field were at least 150 pC/N, and thus the piezoelectric characteristics were excellent. 
     In sample numbers 21 and 22, the numbers of moles a of In were in sample numbers 19 to 22, 1.5 to 10 mol per 100 mols of a main component, the piezoelectric d 33  constants and the piezoelectric d 33  constants in a high electric field were further improved, as compared with sample numbers 19 and 20. It was also found that the firing temperature ranges ΔT were also increased. This is probably because when the In content was less than 1.5 mol, a matching layer between (K 0.5 Na 0.5 )NbO 3  and (Na 0.5 Bi 0.5 )TiO 3  was insufficiently formed, the piezoelectric characteristics became slightly poorer, and the firing temperature range ΔT was as narrow as 10 degrees C. or less, but when the In content was at least 1.5 mol, a desired matching layer was formed and thereby a desired stable piezoelectric ceramic composition was prepared. 
     In sample numbers 24 to 26 containing different components of (M1 0.5 Bi 0.5 )M2O 3  within the scope of the present invention, it was found that the piezoelectric d 33  constants were at least 105 pC/N, the piezoelectric d 33  constants in a high electric field were at least 150 pC/N, and thus the piezoelectric characteristics were excellent. It was also found that the firing temperature range ΔT could also be increased to 35 to 40 degrees C. Thus, it was shown that at least one element selected from the group consisting of Na and K could be used as M1, and at least one element selected from the group consisting of Ti, Zr and Sn could be used as M2. 
     In sample number 27, which did not contain (M1 0.5 Bi 0.5 )M2O 3  in the composition, the piezoelectric d 33  constant was less than 105 pC/N and a piezoelectric d 33  constant in a high electric field was less than 150 pC/N. Thus, it was shown that sample number 27 could not have desired excellent piezoelectric characteristics. 
     Embodiment 2 
     K 2 CO 3 , Na 2 CO 3 , Li 2 CO 3 , Nb 2 O 5 , Ta 2 O 5 , Sb 2 O 5 , Bi 2 O 3 , TiO 2  and In 2 O 3  were prepared as raw materials for ceramics. These raw materials for ceramics were weighed to prepare the compositions shown in Table 3. Test specimens of sample numbers 31 to 55 were produced by the same method and procedures as in Example 1. The firing temperature range ΔT was also determined as in Example 1. 
     The relative dielectric constant ∈r, the electromechanical coupling factor kp, the piezoelectric d 33  constant, the piezoelectric d 33  constant in a high electric field, and the Curie point Tc were determined by the method and procedures in Example 1. 
     Table 3 illustrates the compositions of sample numbers 31 to 55. Table 4 illustrates the measurements and the firing temperature ranges ΔT for sample numbers 31 to 55. 
     
       
         
           
               
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                   
                 Composition: 100{(1 − 
               
               
                   
                 x)(K 1−a−b Na a Li b ) m (Nb 1−c−d Ta c Sb d )O 3 —x(Na 0.5 Bi 0.5 ) n TiO 3 } + 
               
               
                 Sample 
                 In 2 O 3   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                  No. 
                 x 
                 a 
                 b 
                 c 
                 d 
                 m 
                 n 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 31 
                 0.005 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 1 
               
               
                 32 
                 0.1 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 1 
               
               
                 33 
                 0.3 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 1 
               
               
                 34 
                 0.5 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 1 
               
               
                  35* 
                 0.6 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 1 
               
               
                 36 
                 0.05 
                 0 
                 0 
                 0 
                 0 
                 0.98 
                 1 
               
               
                 37 
                 0.05 
                 0.9 
                 0 
                 0 
                 0 
                 0.98 
                 1 
               
               
                  38* 
                 0.05 
                 0.95 
                 0 
                 0 
                 0 
                 0.98 
                 1 
               
               
                 39 
                 0.05 
                 0.35 
                 0.3 
                 0 
                 0 
                 0.98 
                 1 
               
               
                  40* 
                 0.05 
                 0.3 
                 0.4 
                 0 
                 0 
                 0.98 
                 1 
               
               
                 41 
                 0.005 
                 0.5 
                 0 
                 0.5 
                 0 
                 0.98 
                 1 
               
               
                  42* 
                 0.005 
                 0.5 
                 0 
                 0.6 
                 0 
                 0.98 
                 1 
               
               
                 43 
                 0.005 
                 0.5 
                 0 
                 0 
                 0.1 
                 0.98 
                 1 
               
               
                  44* 
                 0.005 
                 0.5 
                 0 
                 0 
                 0.2 
                 0.98 
                 1 
               
               
                  45* 
                 0.05 
                 0.5 
                 0 
                 0 
                 0 
                 0.80 
                 1 
               
               
                 46 
                 0.05 
                 0.5 
                 0 
                 0 
                 0 
                 0.90 
                 1 
               
               
                 47 
                 0.05 
                 0.5 
                 0 
                 0 
                 0 
                 0.95 
                 1 
               
               
                 48 
                 0.05 
                 0.5 
                 0 
                 0 
                 0 
                 0.99 
                 1 
               
               
                 49 
                 0.05 
                 0.5 
                 0 
                 0 
                 0 
                 1.00 
                 1 
               
               
                 50 
                 0.05 
                 0.5 
                 0 
                 0 
                 0 
                 1.10 
                 1 
               
               
                  51* 
                 0.05 
                 0.5 
                 0 
                 0 
                 0 
                 1.20 
                 1 
               
               
                  52* 
                 0.005 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 0.8 
               
               
                 53 
                 0.005 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 0.9 
               
               
                 54 
                 0.005 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 1.1 
               
               
                  55* 
                 0.005 
                 0.5 
                 0 
                 0 
                 0 
                 0.98 
                 1.2 
               
               
                   
               
               
                 *means outside of the scope of the present invention. 
               
            
           
         
       
     
     
       
         
           
               
               
               
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                   
                 Piezoelectric d 33   
                   
                   
               
               
                   
                 Relative 
                 Electromechanical 
                 Piezoelectric d 33   
                 constant in a high 
                   
                 Firing temperature 
               
               
                 Sample 
                 dielectric 
                 coupling factor kp 
                 constant 
                 electric field 
                 Curie point Tc 
                 range ΔT 
               
               
                 No. 
                 constant εr 
                 (%) 
                 (pC/N) 
                 (pC/N) 
                 (° C.) 
                 (° C.) 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                 31 
                 456 
                 43.2 
                 162 
                 267 
                 380 
                 25 
               
               
                 32 
                 589 
                 44.2 
                 182 
                 296 
                 350 
                 30 
               
               
                 33 
                 1021 
                 42.3 
                 232 
                 380 
                 260 
                 35 
               
               
                 34 
                 1523 
                 32.3 
                 212 
                 345 
                 150 
                 35 
               
            
           
           
               
               
            
               
                  35* 
                 No piezoelectricity 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 36 
                 976 
                 31.2 
                 171 
                 284 
                 340 
                 20 
               
               
                 37 
                 1056 
                 27.6 
                 153 
                 255 
                 310 
                 35 
               
            
           
           
               
               
            
               
                  38* 
                 No piezoelectricity 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 39 
                 778 
                 41.2 
                 192 
                 314 
                 310 
                 35 
               
            
           
           
               
               
            
               
                  40* 
                 No piezoelectricity 
               
            
           
           
               
               
               
               
               
               
               
            
               
                 41 
                 1643 
                 33.4 
                 225 
                 368 
                 130 
                 35 
               
               
                  42* 
                 2120 
                 5.9 
                 53 
                 70 
                 50 
                 35 
               
               
                 43 
                 1420 
                 38.4 
                 243 
                 390 
                 180 
                 35 
               
            
           
           
               
               
            
               
                  44* 
                 No piezoelectricity 
               
            
           
           
               
               
               
               
               
               
               
            
               
                  45* 
                 678 
                 10.8 
                 53 
                 60 
                 310 
                 25 
               
               
                 46 
                 756 
                 42.1 
                 204 
                 330 
                 310 
                 35 
               
               
                 47 
                 762 
                 46.3 
                 221 
                 364 
                 310 
                 35 
               
               
                 48 
                 682 
                 49.3 
                 223 
                 366 
                 310 
                 35 
               
               
                 49 
                 583 
                 28.4 
                 109 
                 153 
                 310 
                 35 
               
               
                 50 
                 563 
                 27.8 
                 105 
                 150 
                 310 
                 35 
               
            
           
           
               
               
               
            
               
                  51* 
                 — 
                 Poor sintering 
               
            
           
           
               
               
               
               
               
               
               
            
               
                  52* 
                 682 
                 11.3 
                 55 
                 73 
                 390 
                 35 
               
               
                 53 
                 665 
                 35.2 
                 163 
                 271 
                 390 
                 35 
               
               
                 54 
                 693 
                 34.3 
                 154 
                 256 
                 390 
                 35 
               
               
                  55* 
                 685 
                 11.0 
                 50 
                 68 
                 390 
                 35 
               
               
                   
               
               
                 *means outside of the scope of the present invention. 
               
            
           
         
       
     
     In sample number 35, x was 0.6, i.e., was more than 0.5, and the molar amount of a third component (Na 0.5 Bi 0.5 )TiO 3  was excessive. Thus, sample number 35 was poorly polarized and did not exhibit piezoelectricity. By contrast, it was shown that when x was in the range of 0.005 to 0.5, in sample numbers 31 to 34, a piezoelectric ceramic electronic component having a piezoelectric d 33  constant of at least 105 pC/N and a piezoelectric d 33  constant in a high electric field of at least 150 pC/N and exhibiting excellent piezoelectric characteristics could be produced. 
     In sample number 38, a was 0.95, i.e., was more than 0.9. Thus, the molar ratio of Na was excessive and exceeded the solubility limit with K. Thus, sample number 38 exhibited no piezoelectricity. 
     By contrast, it was shown in sample numbers 36 and 37 that when a was in the range of 0 to 0.9, a piezoelectric ceramic electronic component having a piezoelectric d 33  constant of at least 105 pC/N and a piezoelectric d 33  constant in a high electric field of at least 150 pC/N and exhibiting excellent piezoelectric characteristics could be produced. 
     In sample number 40, b was 0.4, that is was more than 0.3. The molar ratio of Li was too large to form a ferroelectric phase. Thus, sample number 40 exhibited no piezoelectricity. 
     By contrast, it was shown in sample number 39 that when b was 0.3, a piezoelectric ceramic electronic component having a piezoelectric d 33  constant of at least 105 pC/N and a piezoelectric d 33  constant in a high electric field of at least 150 pC/N and exhibiting excellent piezoelectric characteristics could be produced. 
     In sample number 42 where c was 0.6, i.e., was more than 0.5, the piezoelectric d 33  constant was as low as 53 pC/N, the piezoelectric d 33  constant in a high electric field was as low as 70 pC/N, and thus the piezoelectric characteristics were poor. 
     By contrast, it was shown in sample number 41 that when c was 0.5, a piezoelectric ceramic electronic component having a piezoelectric d 33  constant of at least 105 pC/N and a piezoelectric d 33  constant in a high electric field of at least 150 pC/N and exhibiting excellent piezoelectric characteristics could be produced. 
     In sample number 44, d was 0.2 and thus was more than 0.1. Thus, Sb was excessive and the Curie point Tc was decreased. Sample number 44 did not exhibit piezoelectricity. 
     By contrast, it was shown in sample number 43 that when d was 0.1, a piezoelectric ceramic electronic component having a piezoelectric d 33  constant of at least 105 pC/N and a piezoelectric d 33  constant in a high electric field of at least 150 pC/N and exhibiting excellent piezoelectric characteristics could be produced. 
     In sample number 45, m was 0.80 and was thus less than 0.9, and the piezoelectric d 33  constant was as low as 53 pC/N, the piezoelectric d 33  constant in a high electric field was as low as 60 pC/N, and thus the piezoelectric characteristics were poor. 
     In sample number 51, m was 1.20 and was therefore more than 1.1. This caused poor sintering. 
     By contrast, m in sample numbers 46 to 50 was in the range of 0.9 to 1.1. Thus, piezoelectric ceramic electronic components having a piezoelectric d 33  constant of at least 100 pC/N and a piezoelectric d 33  constant in a high electric field of at least 200 pC/N and exhibiting excellent piezoelectric characteristics could be produced. 
     In particular, it was found that when m was in the range of 0.9 to 0.99, as in sample numbers 46 to 48, the piezoelectric d 33  constants were at least 200 pC/N, and the piezoelectric d 33  constants in a high electric field were at least 330 pC/N, and thus the piezoelectric characteristics could further be improved, as compared with sample numbers 49 and 50. 
     The reason for a slight degradation in the piezoelectric characteristics when m is more than 0.99 is probably that the amount of a component that is to constitute an A site, such as K, increases, and thus an element that is not involved in the synthesis of a solid solution reacts preferentially with a tetravalent element constituting a B site of a third component, such as Ti, to form a secondary phase that partly exhibits no piezoelectricity. 
     In sample number 52, it was found that when n was 0.8 and was thus less than 0.9, the piezoelectric d 33  constant was as low as 55 pC/N, the piezoelectric d 33  constant in a high electric field was as low as 73 pC/N, and thus the piezoelectric characteristics were poor. 
     In sample number 55, n was 1.2 and was therefore more than 1.1, and the piezoelectric d 33  constant was as low as 50 pC/N, the piezoelectric d 33  constant in a high electric field was as low as 68 pC/N, and thus the piezoelectric characteristics were poor. 
     By contrast, n was in the range of 0.9 to 1.1 in sample numbers 53 and 54. Thus, piezoelectric ceramic electronic components having a piezoelectric d 33  constant of at least 105 pC/N and a piezoelectric d 33  constant in a high electric field of at least 150 pC/N and exhibiting excellent piezoelectric characteristics could be produced. 
     These results showed that when the molar ratios of x, a, b, c, d, m and n in a main component are in the ranges of 0.005≦x≦0.5, 0≦a≦0.9, 0≦b≦0.3, 0≦a+b≦0.9, 0≦c≦0.5, 0≦d≦0.1, 0.9≦m≦1.1, and 0.9≦n≦1.1, a piezoelectric ceramic electronic component having a piezoelectric d 33  constant of at least 105 pC/N and a piezoelectric d 33  constant in a high electric field of at least 150 pC/N and exhibiting excellent piezoelectric characteristics can be produced. 
     Embodiment 3 
     A predetermined amount of Mn, Ni, Fe, Zn, Cu or Mg was added to the composition of sample number 1. Piezoelectric characteristics and the firing temperature range ΔT were determined. 
     More specifically, K 2 CO 3 , Na 2 CO 3 , Nb 2 O 5 , Bi 2 O 3 , TiO 2 , In 2 O 3 , MnCO 3 , NiO, Fe 2 O 3 , ZnO, CuO and MgCO 3  were prepared as raw materials for ceramics. These raw materials for ceramics were weighed to prepare compositions shown in Table 7. Test specimens of sample numbers 61 to 70 were produced by the same method and procedures as in Example 1. The firing temperature range ΔT was also determined as in Example 1. 
     The relative dielectric constant ∈r, the electromechanical coupling factor kp, the piezoelectric d 33  constant, the piezoelectric d 33  constant in a high electric field, and the Curie point Tc were determined in sample numbers 61 to 70 by the method and procedures in Example 1. 
     Table 5 illustrates the compositions of sample numbers 61 to 70, various measurements, and the firing temperature ranges ΔT, together with the measurements and the firing temperature range ΔT in sample number 1. 
     
       
         
           
               
               
             
               
                   
                 TABLE 5 
               
             
            
               
                   
                   
               
               
                   
                 100{0.95(K 0.5 Na 0.5 ) 0.98 NbO 3 —0.05(Na 0.5 Bi 0.5 )TiO 3 } + In 2 O 3  + β[Z q+ ][O 2− ] (q/2)   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                   
                   
                   
                 Relative 
                   
                   
                 Piezoelectric d 33   
                   
                   
               
               
                   
                   
                   
                 dielectric 
                 Electromechanical coupling 
                 Piezoelectric d 33   
                 constant in a high 
                   
                 Firing temperature 
               
               
                 Sample 
                   
                 β 
                 constant εr 
                 factor kp 
                 constant 
                 electric field 
                 Curie point Tc 
                 range ΔT 
               
               
                 No. 
                 Z 
                 (mol) 
                 εr 
                 (%) 
                 (pC/N) 
                 (pC/N) 
                 (° C.) 
                 (° C.) 
               
               
                   
               
            
           
           
               
               
               
               
               
               
               
               
               
            
               
                  1 
                 — 
                 0 
                 790 
                 50.1 
                 242 
                 393 
                 310 
                 35 
               
               
                 61 
                 Mn 
                 1 
                 612 
                 38.2 
                 166 
                 265 
                 310 
                 55 
               
               
                 62 
                 Ni 
                 1 
                 644 
                 40.8 
                 181 
                 286 
                 310 
                 50 
               
               
                 63 
                 Fe 
                 1 
                 880 
                 39.6 
                 206 
                 329 
                 310 
                 55 
               
               
                 64 
                 Zn 
                 1 
                 586 
                 35.0 
                 161 
                 251 
                 310 
                 60 
               
               
                 65 
                 Cu 
                 1 
                 589 
                 36.3 
                 163 
                 248 
                 310 
                 60 
               
               
                 66 
                 Mg 
                 1 
                 850 
                 37.5 
                 191 
                 298 
                 310 
                 50 
               
               
                 67 
                 Mn 
                 0.1 
                 751 
                 41.7 
                 213 
                 337 
                 310 
                 45 
               
               
                 68 
                 Mn 
                 5 
                 604 
                 36.6 
                 162 
                 251 
                 310 
                 55 
               
               
                 69 
                 Mn 
                 10 
                 505 
                 32.3 
                 126 
                 190 
                 310 
                 50 
               
               
                  70* 
                 Mn 
                 15 
                 — 
                 — 
                 — 
                 — 
                 — 
                 Poor sintering 
               
               
                   
               
               
                 *means outside of the scope of the present invention (Claim 4). 
               
            
           
         
       
     
     As is evident from Table 5, 1 to 10 mol of Mn, Ni, Fe, Zn, Cu, or Mg was added to 100 mol of a main component in sample numbers 61 to 69. Compared with sample number 1, while the piezoelectric d 33  constants and the piezoelectric d 33  constants in a high electric field were slightly decreased, the piezoelectric d 33  constants were at least 105 pC/N, the piezoelectric d 33  constants in a high electric field were at least 150 pC/N, and the firing temperature ranges ΔT for stable sintering were increased to 45 to 60 degrees C. Thus, it was found that the firing temperature ranges ΔT were wider by 10 to 25 degrees C. than sample number 1, and firing was possible in a wider temperature range ΔT. 
     In sample number 70, the molar amount of Mn was as large as 15 mol and was thus more than 10 mols per 100 mols of the main component. This caused poor sintering. 
     These results showed that the addition of as in sample numbers 46 to 48, 1 to 10 mol of Mn, Ni, Fe, Zn, Cu or Mg per 100 mols of a main component can further increase the firing temperature range ΔT.