Ferroelectric ceramic composition
This invention relates to ferroelectric ceramic compositions of a ternary system Pb(Sn.sub.αSb 1   - .sub.α)O 3  --PbTiO 3  --PbZrO 3  which is stable in piezoelectric characteristics. 
     It is known that ceramic compositions of the system PbTiO 3  --PbZrO 3  exhibit desirable piezoelectric characteristics useful for use as piezoelectric ceramic materials, and various kinds of modified ceramics have been reported. These ceramic materials are roughly divided into two main groups, i.e., a hard type and a soft type. One of the representatives of the hard type is a ceramic material of the system PbTiO 3  --PbZrO 3  containing Mn, Fe or Ni and that of the soft type is a ceramic material of the system PbTiO 3  --PbZrO 3  containing Nb or Sb. These ceramic materials exhibit desirable piezoelectric characteristics, but the ceramic materials of the soft type have advantages such as that the aging thereof is extremely great. For example, if a ceramic material of the soft type was compulsorily exposed to heat aging at 150°C, its piezoelectric characteristics such as the electromechanical coupling coefficient kp deteriorate greatly in proportion to the repeated times of application of the heat aging. It is therefore considerably difficult to obtain ceramic products having desired characteristics, for example, such as ceramic filters for the objective frequency. 
     It is therefore an object of the present invention to provide ferroelectric ceramic compositions of which the aging is very small while they are of the soft type. 
     According to this invention, there is provided a ferroelectric ceramic composition of a ternary system Pb(Sn.sub.αSb 1   - .sub.α)O 3  --PbTiO 3  --PbZrO 3  comprising a solid solution represented by the general formula: 
     
         xPb(Sn.sub.αSb.sub.1.sub.-.sub.α)O.sub.3 --yPbTiO.sub.3 --zPbZrO.sub.3 
    
     wherein 
     x + y + z = 1.00 
     1/4 ≦ α ≦ 3/4 
     Said composition being in a polygonal area defined by the points A, B, C, D, E and F in FIG. 1, the sets of mol fractions of the three components at said points being as follows: 
     
                 x         y           z                                           
______________________________________                                    
A         0.01        0.60        0.39                                    
B         0.01        0.30        0.69                                    
C         0.15        0.25        0.60                                    
D         0.25        0.25        0.50                                    
E         0.25        0.50        0.25                                    
F         0.15        0.60        0.25                                    
______________________________________                                    
 
    
     If the value of α is less than 1/2, several problems arise along with it. It is therefore preferred to limit the compositional area in response to the value of α as follows: 
     When 1/3 ≦ α &lt; 1/2, it is preferred to limit the compositional area to a polygonal area defined by the points A, B, C, D 1 , E 1 , and F in FIG. 1, the sets of mol fractions of the three components at said points being as follows: 
     
                  x        y          z                                            
______________________________________                                    
A          0.01       0.60       0.39                                     
B          0.01       0.30       0.69                                     
C          0.15       0.25       0.60                                     
D.sub.1    0.20       0.25       0.55                                     
E.sub.1    0.20       0.55       0.25                                     
F          0.15       0.60       0.25                                     
______________________________________                                    
 
    
     When 1/4 ≦ α &lt; 1/3, it is preferred to limit the compositional area to a polygonal area defined by the points A, B, C, D 2 , E 2  and F in FIG. 1, the sets of mol fractions of the three components at said points being as follows: 
     
         x              y          z                                               
______________________________________                                    
A       0.01       0.60       0.39                                        
B       0.01       0.30       0.69                                        
C       0.15       0.25       0.60                                        
D.sub.2 0.15       0.35       0.50                                        
E.sub.2 0.15       0.50       0.35                                        
F       0.15       0.60       0.25                                        
______________________________________                                    
 
    
     The piezoelectric ceramics according to the invention may be prepared in a manner conventionally adapted for the preparation of piezoelectric ceramics. 
     The piezoelectric ceramics which are the compositions of a ternary system Pb(Sn.sub.αSb 1   - .sub.α)O 3  --PbTiO 3  --PbZrO 3  have high resistance to heat aging, in other words, high thermostability in piezoelectric characteristics such as electromechanical coupling coefficient(kp), mechanical quality factor (Qm) and dielectric constant(ε s ). In addition, if they are applied to energy trapped mode ceramic resonators, the difference (Δf) between the antiresonance frequency (fa) and resonance frequency (fo) varies scarcely. Moreover, the temperature coefficients (TC) of the antiresonance and resonance frequencies of the piezoelectric ceramics are small in wide compositional area. Thus, these ceramics according to the present invention are suitable for use as ceramic filters, vibrators, acoustic elements, piezoelectric ignition elements and the like. 
    
    
     The invention will be further apparent from the following description with reference to examples and the accompanying drawings, in which: 
     FIG. 1 is a triangular diagram showing the area of the ferroelectric ceramic compositions according to the invention; 
     FIGS. 2 through 7 are the graphs showing the changes of the temperature coefficient of frequencies (from -20°C to +80°C) as a function of molar ratio of PbTiO 3  /PbZrO 3  ; and 
     FIG. 8 is a graph showing the relation between the contents of Sn, Sb and the degree of sintering. 
    
    
     EXAMPLES 
     The compounds PbO (or Pb 3  O 4 ), SnO 2 , Sb 2  O 3 , TiO 2  and ZrO 2  were used as raw materials. These raw materials were individually weighed to obtain a mixture having the compositional proportions shown in Table 1, and then mixed by the wet process for about 20 hours. After drying, the resultant mixture was presintered at about 750° - 850°C for 2 hours. The presintered body was milled by the wet process with a suitable organic binder for 10 to 20 hours, dried and passed through as 80 mesh sieve to obtain minus sieve powder. The thus obtained powder was molded into a disk with a diameter of 22 mm and a thickness of 1.2 mm at a pressure of 750 - 1000 kg/cm 2  and then sintered at a temperature of 1150° - 1250°C for 2 hours in order to obtain a sample of the piezoelectric ceramics. 
     
                       Table 1                                                     
______________________________________                                    
Sample      Composition (Mol fraction)                                    
No.             α  x      y      z                                  
______________________________________                                    
1      *        1        0.03   0.44   0.53                               
2      *        1        0.03   0.46   0.51                               
3      *        1        0.03   0.48   0.49                               
4      *        1        0.03   0.50   0.47                               
5      *        1        0.05   0.44   0.51                               
6      *        1        0.05   0.46   0.49                               
7      *        1        0.05   0.48   0.47                               
8      *        1        0.05   0.50   0.45                               
9      *        1        0.10   0.44   0.46                               
10     *        1        0.10   0.46   0.44                               
11     *        1        0.10   0.48   0.42                               
12     *        1        0.10   0.50   0.40                               
13     A        3/4      0.01   0.60   0.39                               
14     B        3/4      0.01   0.30   0.69                               
15              3/4      0.03   0.44   0.53                               
16              3/4      0.03   0.50   0.47                               
17              3/4      0.05   0.44   0.51                               
18              3/4      0.05   0.50   0.45                               
19              3/4      0.10   0.44   0.46                               
20              3/4      0.10   0.50   0.40                               
21     C        3/4      0.15   0.25   0.60                               
22     F        3/4      0.15   0.60   0.25                               
23     D        3/4      0.25   0.25   0.50                               
24     E        3/4      0.25   0.50   0.25                               
25     A        2/3      0.01   0.60   0.39                               
26     B        2/3      0.01   0.30   0.69                               
27              2/3      0.01   0.44   0.55                               
28              2/3      0.01   0.46   0.53                               
29              2/3      0.01   0.48   0.51                               
30              2/3      0.01   0.50   0.49                               
31              2/3      0.03   0.44   0.53                               
32              2/3      0.03   0.46   0.51                               
33              2/3      0.03   0.48   0.49                               
34              2/3      0.03   0.50   0.47                               
35              2/3      0.05   0.44   0.51                               
36              2/3      0.05   0.46   0.49                               
37              2/3      0.05   0.48   0.47                               
38              2/3      0.05   0.50   0.45                               
39              2/3      0.06   0.44   0.50                               
40              2/3      0.06   0.46   0.48                               
41              2/3      0.06   0.48   0.46                               
42              2/3      0.06   0.50   0.44                               
43              2/3      0.08   0.44   0.48                               
44              2/3      0.08   0.46   0.46                               
45              2/3      0.08   0.48   0.44                               
46              2/3      0.08   0.50   0.42                               
47              2/3      0.10   0.44   0.46                               
48              2/3      0.10   0.46   0.44                               
49              2/3      0.10   0.48   0.42                               
50              2/3      0.10   0.50   0.40                               
51     C        2/3      0.15   0.25   0.60                               
52     F        2/3      0.15   0.60   0.25                               
53     D        2/3      0.20   0.25   0.55                               
54     E        2/3      0.20   0.55   0.25                               
55     A        1/2      0.01   0.60   0.39                               
56     B        1/2      0.01   0.30   0.69                               
57              1/2      0.02   0.42   0.56                               
58              1/2      0.02   0.44   0.54                               
59              1/2      0.02   0.46   0.52                               
60              1/2      0.02   0.48   0.50                               
61              1/2      0.02   0.50   0.48                               
62              1/2      0.03   0.42   0.55                               
63              1/2      0.03   0.43   0.54                               
64              1/2      0.03   0.44   0.53                               
65              1/2      0.03   0.45   0.52                               
66              1/2      0.03   0.46   0.51                               
67              1/2      0.03   0.47   0.50                               
68              1/2      0.03   0.48   0.49                               
69              1/2      0.03   0.49   0.48                               
70              1/2      0.03   0.50   0.47                               
71              1/2      0.03   0.51   0.46                               
72              1/2      0.03   0.52   0.45                               
73              1/2      0.04   0.42   0.54                               
74              1/2      0.04   0.44   0.52                               
75              1/2      0.04   0.46   0.50                               
76              1/2      0.04   0.48   0.48                               
77              1/2      0.04   0.50   0.46                               
78              1/2      0.05   0.42   0.53                               
79              1/2      0.05   0.43   0.52                               
80              1/2      0.05   0.44   0.51                               
81              1/2      0.05   0.45   0.50                               
82              1/2      0.05   0.46   0.49                               
83              1/2      0.05   0.47   0.48                               
84              1/2      0.05   0.48   0.47                               
85              1/2      0.05   0.49   0.46                               
86              1/2      0.05   0.50   0.45                               
87              1/2      0.05   0.51   0.44                               
88              1/2      0.05   0.52   0.43                               
89              1/2      0.06   0.42   0.52                               
90              1/2      0.06   0.44   0.50                               
91              1/2      0.06   0.46   0.48                               
92              1/2      0.06   0.48   0.46                               
93              1/2      0.06   0.50   0.44                               
94              1/2      0.10   0.44   0.46                               
95              1/2      0.10   0.46   0.44                               
96              1/2      0.10   0.48   0.42                               
97              1/2      0.10   0.50   0.40                               
98     C        1/2      0.15   0.25   0.60                               
99     F        1/2      0.15   0.60   0.25                               
100    D        1/2      0.25   0.25   0.50                               
101    E        1/2      0.25   0.50   0.25                               
102    A        1/3      0.01   0.60   0.39                               
103    B        1/3      0.01   0.30   0.69                               
104             1/3      0.01   0.44   0.55                               
105             1/3      0.01   0.46   0.53                               
106             1/3      0.01   0.48   0.51                               
107             1/3      0.01   0.50   0.49                               
108             1/3      0.03   0.44   0.53                               
109             1/3      0.03   0.46   0.51                               
110             1/3      0.03   0.48   0.49                               
111             1/3      0.03   0.50   0.47                               
112             1/3      0.05   0.44   0.51                               
113             1/3      0.05   0.46   0.49                               
114             1/3      0.05   0.48   0.47                               
115             1/3      0.05   0.50   0.45                               
116             1/3      0.06   0.44   0.50                               
117             1/3      0.06   0.46   0.48                               
118             1/3      0.06   0.48   0.46                               
119             1/3      0.06   0.50   0.44                               
120             1/3      0.08   0.44   0.48                               
121             1/3      0.08   0.46   0.46                               
122             1/3      0.08   0.48   0.44                               
123             1/3      0.08   0.50   0.42                               
124             1/3      0.10   0.44   0.46                               
125             1/3      0.10   0.46   0.44                               
126             1/3      0.10   0.48   0.42                               
127             1/3      0.10   0.50   0.40                               
128    C        1/3      0.15   0.25   0.60                               
129    F        1/3      0.15   0.60   0.25                               
130    D.sub.1  1/3      0.20   0.25   0.55                               
131    E.sub.1  1/3      0.20   0.55   0.25                               
132    A        1/4      0.01   0.60   0.39                               
133    B        1/4      0.01   0.30   0.69                               
134             1/4      0.03   0.44   0.53                               
135             1/4      0.03   0.50   0.47                               
136             1/4      0.05   0.44   0.51                               
137             1/4      0.05   0.50   0.45                               
138    C        1/4      0.15   0.25   0.60                               
139    F        1/4      0.15   0.60   0.25                               
140             1/4      0.15   0.44   0.46                               
141             1/4      0.15   0.50   0.40                               
142    D.sub.2  1/4      0.15   0.35   0.50                               
143    E.sub.2  1/4      0.15   0.50   0.35                               
144    *        0        0.03   0.44   0.53                               
145    *        0        0.03   0.46   0.51                               
146    *        0        0.03   0.48   0.49                               
147    *        0        0.03   0.50   0.47                               
148    *        0        0.05   0.44   0.51                               
149    *        0        0.05   0.46   0.49                               
150    *        0        0.05   0.48   0.47                               
151    *        0        0.05   0.50   0.45                               
152    *        0        0.10   0.44   0.46                               
153    *        0        0.10   0.46   0.44                               
154    *        0        0.10   0.48   0.42                               
155    *        0        0.10   0.50   0.40                               
______________________________________                                    
 
    
     Each plane of the sample was fitted with a silver electrode by stoving and then polarized in an insulating oil by applying a DC voltage of 3.0 - 4.0 KV/mm. After the poling treatment, the sample was kept in a drier for 1 hour at 150°C to carry out the first heat aging, cooled to room temperature and then kept again in the drier under the same conditions for 1 hour to carry out the second heat aging. 
     The heat aging is usually made just after the poling treatment in order to stabilize the electromechanical coupling coefficient of the ceramics so that the results after the second heat aging show the heat aging characteristics of the ceramics. 
     The measurements of the piezoelectric characteristics of the samples were made just after each heat aging to evaluate the thermostability thereof. The dielectric constant (ε s ) was measured with a capacitance bridge, and the electromechanical coupling coefficient (kp) and the mechanical quality factor (Qm) were measured with the IRE standard circuits. Results are shown in Table 2 in which the results after the first heat aging are listed in the columns indicated by (1) and those after the second heat aging are listed in the columns indicated by (2). 
     The change rate of electromechanical coupling coefficient is given by the following equation: ##EQU1## 
     The negative value of the change rate in Table 2 means that the value of the electromechanical coupling coefficient (kp) was increased by the second heat aging. 
     Results for samples Nos. 1 to 12 were excluded from Table 2 since they have relatively high values of the mechanical quality factor (Qm &gt; 140) and show little changes in their piezoelectric characteristics such as dielectric constant, electromechanical coupling coefficient and mechanical quality factor. Results for samples Nos. 101 to 108 were also excluded from the table since sintered bodies thereof were never obtained and the resulant products exhibit no piezoelectric characteristics. 
     Reference samples of a soft type were prepared in the same manner as mentioned above. All of the reference samples consist of the composition of a system 0.48PbTiO 3  - 0.52PbZrO 3  containing 1 wt % of Nb 2  O 5 . The measurements of the electromechanical coupling coefficient of these reference samples were made after each heat aging. Results are shown in Table 3 in which the results after the first heat aging are summarized in the column indicated by (1) and those after the second heat aging are summarized in the column indicated by (2). The values in the respective columns (1) and (2) are the maximum and minimum values of the results for five samples. The minimum change rate was obtained by using the maximum value in the column (2) and the minimun value in the column (1). The maximum change rate was obtained by using the maximum value in the column (1) and the minimum value in the column (2). 
     
                                           Table 2                                 
__________________________________________________________________________
      Dielectric                                                          
              Electro-Mechanical                                          
                            Mechanical                                    
Constant                                                                  
      Coupling Coefficient                                                
              Quality Factor                                              
Sample                                                                    
      ε.sub.s                                                     
              Kp (%)        Qm                                            
                      Change                                              
No.   (1) (2) (1) (2) Rate(%)                                             
                            (1) (2)                                       
__________________________________________________________________________
1  *  601 --  36.8                                                        
                  --  --    188 --                                        
2  *  704 --  44.0                                                        
                  --  --    177 --                                        
3  *  1366                                                                
          --  46.5                                                        
                  --  --    163 --                                        
4  *  989 --  27.8                                                        
                  --  --    182 --                                        
5  *  577 --  38.3                                                        
                  --  --    202 --                                        
6  *  686 --  45.7                                                        
                  --  --    184 --                                        
7  *  1406                                                                
          --  46.6                                                        
                  --  --    170 --                                        
8  *  947 --  26.7                                                        
                  --  --    177 --                                        
9  *  605 --  39.0                                                        
                  --  --    183 --                                        
10 *  758 --  46.4                                                        
                  --  --    194 --                                        
11 *  1361                                                                
          --  38.6                                                        
                  --  --    143 --                                        
12 *  1028                                                                
          --  31.7                                                        
                  --  --    173 --                                        
13 A  641 634 22.3                                                        
                  21.1                                                    
                      5.4   98  98                                        
14 B  635 629 29.7                                                        
                  29.3                                                    
                      1.3   103 105                                       
15    643 632 50.3                                                        
                  48.5                                                    
                      3.6   152 149                                       
16    1033                                                                
          1021                                                            
              31.2                                                        
                  30.7                                                    
                      1.6   99  108                                       
17    701 677 45.9                                                        
                  43.8                                                    
                      4.6   143 153                                       
18    1153                                                                
          1113                                                            
              35.6                                                        
                  33.0                                                    
                      7.3   86  88                                        
19    709 708 47.8                                                        
                  46.4                                                    
                      2.9   123 137                                       
20    1243                                                                
          1235                                                            
              39.3                                                        
                  37.2                                                    
                      5.3   89  96                                        
21 C  708 702 33.2                                                        
                  31.2                                                    
                      6.0   100 103                                       
22 F  731 735 32.1                                                        
                  27.5                                                    
                      14.3  111 115                                       
23 D  1018                                                                
          1021                                                            
              25.3                                                        
                  21.8                                                    
                      13.8  128 137                                       
24 E  1103                                                                
          1121                                                            
              24.1                                                        
                  23.3                                                    
                      3.3   126 126                                       
25 A  613 600 25.4                                                        
                  22.2                                                    
                      12.6  89  83                                        
26 B  597 598 23.1                                                        
                  20.3                                                    
                      12.1  82  85                                        
27    622 626 32.1                                                        
                  32.4                                                    
                      -0.9  94  116                                       
28    766 788 33.5                                                        
                  33.5                                                    
                      0.0   78  94                                        
29    966 959 19.2                                                        
                  22.0                                                    
                      -14.6 87  93                                        
30    761 753 18.9                                                        
                  20.0                                                    
                      -5.8  81  88                                        
31    672 661 49.5                                                        
                  50.5                                                    
                      -2.0  99  99                                        
32    826 807 58.0                                                        
                  52.5                                                    
                      9.5   86  84                                        
33    1556                                                                
          1556                                                            
              45.7                                                        
                  46.0                                                    
                      -0.7  81  85                                        
34    1077                                                                
          1068                                                            
              33.8                                                        
                  33.7                                                    
                      0.3   78  93                                        
35    788 777 56.8                                                        
                  54.4                                                    
                      4.2   83  90                                        
36    994 995 66.5                                                        
                  69.0                                                    
                      -3.8  82  82                                        
37    1667                                                                
          1689                                                            
              56.1                                                        
                  55.5                                                    
                      1.1   88  91                                        
38    1228                                                                
          1223                                                            
              43.7                                                        
                  43.9                                                    
                      -0.5  97  99                                        
39    795 783 57.2                                                        
                  54.3                                                    
                      5.1   84  90                                        
40    994 990 65.8                                                        
                  62.0                                                    
                      5.8   76  84                                        
41    1672                                                                
          1658                                                            
              57.8                                                        
                  56.1                                                    
                      2.9   79  85                                        
42    1267                                                                
          1247                                                            
              44.5                                                        
                  44.0                                                    
                      1.1   90  98                                        
43    878 857 56.0                                                        
                  52.6                                                    
                      6.1   81  90                                        
44    1207                                                                
          1200                                                            
              66.0                                                        
                  62.0                                                    
                      6.1   71  80                                        
45    1685                                                                
          1663                                                            
              56.0                                                        
                  54.5                                                    
                      2.7   73  79                                        
46    1275                                                                
          1261                                                            
              46.5                                                        
                  46.0                                                    
                      1.1   87  95                                        
47    890 897 44.2                                                        
                  44.0                                                    
                      0.5   83  85                                        
48    1231                                                                
          1245                                                            
              46.3                                                        
                  45.1                                                    
                      2.6   80  82                                        
49    1701                                                                
          1693                                                            
              50.3                                                        
                  48.9                                                    
                      2.8   73  77                                        
50    1258                                                                
          1249                                                            
              43.2                                                        
                  42.1                                                    
                      2.5   85  89                                        
51 C  683 664 21.1                                                        
                  20.1                                                    
                      4.7   88  92                                        
52 F  813 795 27.5                                                        
                  26.5                                                    
                      3.6   93  99                                        
53 D  962 978 29.0                                                        
                  28.9                                                    
                      0.3   100 102                                       
54 E  998 1001                                                            
              26.3                                                        
                  25.5                                                    
                      3.0   100 97                                        
55    596 592 23.6                                                        
                  23.8                                                    
                      0.8   92  95                                        
56    389 394 25.9                                                        
                  26.3                                                    
                      1.5   103 100                                       
57    604 600 39.6                                                        
                  39.5                                                    
                      0.3   97  81                                        
58    678 679 48.2                                                        
                  48.2                                                    
                      0.0   87  92                                        
59    875 880 55.0                                                        
                  55.1                                                    
                      0.2   68  82                                        
60    1544                                                                
          1549                                                            
              45.3                                                        
                  45.7                                                    
                      0.9   60  77                                        
61    1057                                                                
          1058                                                            
              33.6                                                        
                  34.0                                                    
                      1.2   66  82                                        
62    682 681 49.0                                                        
                  48.8                                                    
                      0.4   98  95                                        
63    730 726 44.1                                                        
                  44.0                                                    
                      0.2   80  79                                        
64    713 699 57.9                                                        
                  58.0                                                    
                      0.2   90  89                                        
65    835 835 61.6                                                        
                  61.2                                                    
                      0.6   78  81                                        
66    905 900 61.7                                                        
                  61.8                                                    
                      0.2   84  80                                        
67    1581                                                                
          1610                                                            
              63.7                                                        
                  63.5                                                    
                      0.3   60  76                                        
68    1725                                                                
          1737                                                            
              54.9                                                        
                  55.9                                                    
                      1.8   82  68                                        
69    1393                                                                
          1396                                                            
              46.0                                                        
                  46.1                                                    
                      0.2   74  83                                        
70    1292                                                                
          1353                                                            
              42.4                                                        
                  43.2                                                    
                      1.9   90  85                                        
71    1067                                                                
          1067                                                            
              36.7                                                        
                  36.8                                                    
                      0.3   95  96                                        
72    911 913 30.5                                                        
                  31.0                                                    
                      1.6   87  107                                       
73    733 730 48.5                                                        
                  47.7                                                    
                      1.6   84  92                                        
74    837 836 62.0                                                        
                  60.5                                                    
                      2.4   71  83                                        
75    1115                                                                
          1139                                                            
              66.4                                                        
                  65.2                                                    
                      1.8   58  74                                        
76    1632                                                                
          1638                                                            
              60.0                                                        
                  59.0                                                    
                      1.7   84  77                                        
77    1272                                                                
          1266                                                            
              46.6                                                        
                  46.4                                                    
                      0.4   79  89                                        
78    800 804 37.1                                                        
                  36.8                                                    
                      0.8   75  88                                        
79    842 851 56.8                                                        
                  54.6                                                    
                      3.8   79  90                                        
80    850 854 57.6                                                        
                  56.8                                                    
                      1.4   86  88                                        
81    979 999 63.1                                                        
                  60.9                                                    
                      3.5   68  77                                        
82    1124                                                                
          1135                                                            
              60.9                                                        
                  59.7                                                    
                      2.0   76  69                                        
83    1676                                                                
          1707                                                            
              70.0                                                        
                  68.2                                                    
                      2.9   58  73                                        
84    1612                                                                
          1680                                                            
              44.3                                                        
                  43.6                                                    
                      1.6   66  75                                        
85    1582                                                                
          1583                                                            
              57.0                                                        
                  56.7                                                    
                      0.5   68  86                                        
86    1270                                                                
          1276                                                            
              45.9                                                        
                  44.0                                                    
                      4.1   95  84                                        
87    1202                                                                
          1199                                                            
              44.5                                                        
                  44.5                                                    
                      0.0   84  100                                       
88    1061                                                                
          1060                                                            
              40.1                                                        
                  40.3                                                    
                      0.5   90  107                                       
89    862 869 34.9                                                        
                  34.6                                                    
                      0.9   94  98                                        
90    934 948 54.5                                                        
                  51.9                                                    
                      4.8   74  86                                        
91    1454                                                                
          1507                                                            
              53.4                                                        
                  55.0                                                    
                      3.0   70  74                                        
92    1772                                                                
          1788                                                            
              55.4                                                        
                  54.8                                                    
                      1.1   73  82                                        
93    1325                                                                
          1332                                                            
              42.3                                                        
                  42.1                                                    
                      0.5   77  93                                        
94    1141                                                                
          1138                                                            
              44.7                                                        
                  42.4                                                    
                      5.1   85  92                                        
95    1551                                                                
          1549                                                            
              51.9                                                        
                  48.5                                                    
                      6.6   73  78                                        
96    1440                                                                
          1415                                                            
              37.7                                                        
                  36.1                                                    
                      4.2   85  89                                        
97    1100                                                                
          1087                                                            
              32.7                                                        
                  33.1                                                    
                      1.2   100 100                                       
98    557 561 29.4                                                        
                  29.1                                                    
                      1.0   93  90                                        
99    572 570 20.8                                                        
                  20.7                                                    
                      0.5   112 111                                       
100   964 967 35.1                                                        
                  35.0                                                    
                      0.3   82  85                                        
101   825 821 22.6                                                        
                  22.4                                                    
                      0.9   106 107                                       
102                                                                       
   A  607 603 24.5                                                        
                  22.4                                                    
                      8.6   92  81                                        
103                                                                       
   B  632 615 27.3                                                        
                  23.8                                                    
                      12.8  83  89                                        
104   574 590 50.8                                                        
                  51.5                                                    
                      -1.4  91  97                                        
105   850 882 62.5                                                        
                  63.5                                                    
                      -1.6  77  74                                        
106   1397                                                                
          1388                                                            
              43.2                                                        
                  43.3                                                    
                      -0.2  37  55                                        
107   810 812 27.5                                                        
                  29.5                                                    
                      -7.3  58  74                                        
108   777 771 59.7                                                        
                  57.5                                                    
                      3.7   88  91                                        
109   1048                                                                
          1062                                                            
              69.0                                                        
                  65.0                                                    
                      5.8   81  81                                        
110   1639                                                                
          1635                                                            
              60.6                                                        
                  58.5                                                    
                      3.5   87  89                                        
111   1230                                                                
          1221                                                            
              45.3                                                        
                  45.0                                                    
                      0.7   97  99                                        
112   955 944 52.5                                                        
                  48.2                                                    
                      8.2   82  88                                        
113   1324                                                                
          1319                                                            
              50.5                                                        
                  49.0                                                    
                      3.0   69  73                                        
114   1508                                                                
          1490                                                            
              41.5                                                        
                  42.0                                                    
                      -1.2  71  76                                        
115   1181                                                                
          1178                                                            
              33.3                                                        
                  33.5                                                    
                      -0.6  84  84                                        
116   895 933 44.0                                                        
                  42.7                                                    
                      3.0   77  80                                        
117   1280                                                                
          1344                                                            
              66.6                                                        
                  63.0                                                    
                      5.4   62  64                                        
118   1630                                                                
          1668                                                            
              53.0                                                        
                  52.2                                                    
                      1.5   72  75                                        
119   1266                                                                
          1286                                                            
              43.7                                                        
                  43.1                                                    
                      1.4   83  88                                        
120   1058                                                                
          1096                                                            
              40.2                                                        
                  38.3                                                    
                      4.7   77  80                                        
121   1533                                                                
          1519                                                            
              50.0                                                        
                  48.5                                                    
                      3.0   75  72                                        
122   1341                                                                
          1359                                                            
              44.0                                                        
                  43.0                                                    
                      2.3   81  84                                        
123   1030                                                                
          1042                                                            
              37.2                                                        
                  36.8                                                    
                      1.1   90  96                                        
124   1108                                                                
          1123                                                            
              36.2                                                        
                  35.0                                                    
                      3.3   73  75                                        
125   1611                                                                
          1638                                                            
              45.9                                                        
                  44.3                                                    
                      3.5   70  77                                        
126   1404                                                                
          1429                                                            
              38.8                                                        
                  38.0                                                    
                      2.1   78  81                                        
127   1129                                                                
          1105                                                            
              32.5                                                        
                  31.5                                                    
                      3.1   82  85                                        
128                                                                       
   C  739 721 31.2                                                        
                  29.6                                                    
                      5.1   79  82                                        
129                                                                       
   F  853 831 33.3                                                        
                  30.2                                                    
                      9.3   87  93                                        
130                                                                       
   D.sub.1                                                                
      973 999 29.9                                                        
                  27.3                                                    
                      8.7   83  85                                        
131                                                                       
   E.sub.1                                                                
      1003                                                                
          1012                                                            
              28.3                                                        
                  26.5                                                    
                      6.4   92  98                                        
132                                                                       
   A  543 534 22.1                                                        
                  21.4                                                    
                      3.2   93  70                                        
133                                                                       
   B  421 401 25.6                                                        
                  24.8                                                    
                      3.1   71  75                                        
134   795 789 59.3                                                        
                  56.5                                                    
                      4.7   88  90                                        
135   1238                                                                
          1226                                                            
              43.2                                                        
                  42.3                                                    
                      2.1   83  99                                        
136   979 962 61.1                                                        
                  50.0                                                    
                      2.2   89  88                                        
137   1121                                                                
          1180                                                            
              38.0                                                        
                  37.9                                                    
                      0.3   87  86                                        
138                                                                       
   C  893 973 48.2                                                        
                  46.1                                                    
                      4.4   86  87                                        
139                                                                       
   F.sub.2                                                                
      1099                                                                
          1121                                                            
              45.0                                                        
                  42.2                                                    
                      6.2   81  83                                        
140   621 635 25.0                                                        
                  24.6                                                    
                      1.6   80  78                                        
141   731 741 26.2                                                        
                  25.1                                                    
                      4.2   75  81                                        
142                                                                       
   D.sub.2                                                                
      997 989 24.3                                                        
                  23.2                                                    
                      4.5   70  76                                        
143                                                                       
   E.sub.2                                                                
      1031                                                                
          1005                                                            
              29.5                                                        
                  27.3                                                    
                      7.5   80  87                                        
144                                                                       
   *  878 869 56.5                                                        
                  56.0                                                    
                      0.9   88  90                                        
145                                                                       
   *  1252                                                                
          1267                                                            
              68.0                                                        
                  63.0                                                    
                      7.4   79  83                                        
146                                                                       
   *  1601                                                                
          1590                                                            
              54.5                                                        
                  53.5                                                    
                      1.8   84  88                                        
147                                                                       
   *  1254                                                                
          1237                                                            
              46.0                                                        
                  46.0                                                    
                      0.0   96  99                                        
148                                                                       
   *  --  --  --  --  --    --  --                                        
149                                                                       
   *  --  --  --  --  --    --  --                                        
150                                                                       
   *  --  --  --  --  --    --  --                                        
151                                                                       
   *  --  --  --  --  --    --  --                                        
152                                                                       
   *  --  --  --  --  --    --  --                                        
153                                                                       
   *  --  --  --  --  --    --  --                                        
154                                                                       
   *  --  --  --  --  --    --  --                                        
155                                                                       
   *  --  --  --  --  --    --  --                                        
__________________________________________________________________________
 
    
     
                       Table 3                                                     
______________________________________                                    
Electromechanical coupling                                                
                     Change Rate                                          
coefficient kp (%)   (%)                                                  
(1)        (2)                                                            
______________________________________                                    
68 - 70    52 - 55       19 - 26                                          
______________________________________                                    
 
    
     As will be evident from Tables 2 and 3, the ceramic compositions of the invention are scarcely changed in their piezoelectric characteristics by the repetition of the heat aging whereas the ceramic composition of the reference samples has a tendency to cause the deterioration of the electromechanical coupling coefficient by the repetition of the heat aging. Thus, it will be noted that the ceramic compositions of this invention are superior in stability to the ceramic composition of the reference samples. 
     The stability of the piezoelectric characteristics is very important in cases where the ceramic compositions are applied to mechanical ceramic filters, ceramic resonators, oscillators and the like. 
     In order to examine the utility of the ceramic compositions of the invention, the ceramic composition are applied to resonators in the following manner. 
     The disk obtained by the above mentioned preparation methos was ground so as to have a thickness of 0.2 mm. The thus obtained thin disk was fitted with a silver electrode layer on each plane thereof and then polarized in the same manner as mentioned above. After a poling treatment, the thin disk was provided with an opposite electrode on each plane thereof to complete the preparation of an energy trapped mode resonator having an intermediate frequency of 10.7 MHz. The resonator was coated by a well-known dip coating method. 
     The measurements of antiresonance and resonance frequencies of the resonator were made before and after the dip coating, whereby an examination was made as to how the difference Δf (= fa - fo) between the antiresonance and resonance frequencies is affected by the heat and the clamping force caused by the hardening of the paints, both of which are applied to the resonator during dip coating. The differences Δf before and after dip coating are shown in Table 4. 
     
                                           Table 4                                 
__________________________________________________________________________
Δf (KHz)         Δf (KHz)                                     
Sample                                                                    
      Before dip                                                          
            After dip                                                     
                  Sample                                                  
                       Before dip                                         
                             After dip                                    
No.   coating                                                             
            coating                                                       
                  No.  coating                                            
                             coating                                      
__________________________________________________________________________
1     347   364   36   673   675                                          
2     453   461   37   611   621                                          
3     450   446   38   510   502                                          
4     150   134   39   631   626                                          
5     433   450   40   668   671                                          
6     511   523   41   676   686                                          
7     498   507   42   530   521                                          
8     135   143   43   560   567                                          
9     492   481   44   607   612                                          
10    573   585   45   638   649                                          
11    500   523   46   508   514                                          
12    210   249   47   465   467                                          
13    --    --    48   478   480                                          
14    180   175   49   515   518                                          
15    515   514   50   449   446                                          
16    216   212   51   --    --                                           
17    461   465   52   --    --                                           
18    253   270   53   170   165                                          
19    492   494   54   --    --                                           
20    373   366   55   --    --                                           
21    233   224   56   --    --                                           
22    119   127   57   293   309                                          
23    --    --    58   436   456                                          
24    --    --    59   515   546                                          
25    --    --    60   451   460                                          
26    --    --    61   126   195                                          
27    253   247   62   459   471                                          
28    310   312   63   505   534                                          
29    231   249   64   505   526                                          
30    --    --    65   535   565                                          
31    600   601   66   545   558                                          
32    688   693   67   572   575                                          
33    661   660   68   586   596                                          
34    331   334   69   469   494                                          
35    607   608   70   424   424                                          
71    282   290   106  651   656                                          
72    265   270   107  230   245                                          
73    435   460   108  559   561                                          
74    540   563   109  639   648                                          
75    569   574   110  664   664                                          
76    597   598   111  500   509                                          
77    444   436   112  500   501                                          
78    357   367   113  415   414                                          
79    465   471   114  450   447                                          
80    509   518   115  350   354                                          
81    514   538   116  300   303                                          
82    529   533   117  635   640                                          
83    601   604   118  577   568                                          
84    450   451   119  500   499                                          
85    567   560   120  389   400                                          
86    450   451   121  542   540                                          
87    427   419   122  501   506                                          
88    328   318   123  211   220                                          
89    259   250   124  312   315                                          
90    467   464   125  468   471                                          
91    541   534   126  379   382                                          
92    561   561   127  218   233                                          
93    460   460   128  172   183                                          
94    417   377   129  199   200                                          
95    498   472   130  117   122                                          
96    392   390   131  --    --                                           
97    228   217   132  --    --                                           
98    207   200   133  --    --                                           
99    --    --    134  569   575                                          
100   234   231   135  450   448                                          
101   --    --    136  518   527                                          
102   --    --    137  361   380                                          
103   --    --    138  472   490                                          
104   580   578   139  400   448                                          
105   668   673   140  --    --                                           
141   --    --                                                            
142   --    --                                                            
143   121   112                                                           
144   523   532                                                           
145   549   558                                                           
146   570   572                                                           
147   510   509                                                           
148   --    --                                                            
149   --    --                                                            
150   --    --                                                            
151   --    --                                                            
152   --    --                                                            
153   --    --                                                            
154   --    --                                                            
155   --    --                                                            
Reference                                                                 
Sample                                                                    
      680   500                                                           
__________________________________________________________________________
 
    
     From this table, it will be seen that the ceramic compositions of the invention are scarcely influenced by the processing whereas the ceramic composition of the reference sample is greatly influenced. Thus, the ceramic compositions of the invention are useful for use as materials for resonators, mechanical ceramic filters and the like. 
     Experiments with respect to the samples having a low electromechanical coupling coefficient less than 25% were omitted since it was difficult to prepare the energy trapped mode resonators for 10.7 MHz. 
     Some of the representatives of the ceramic compositions of the invention were examined as to how the temperature coefficients (TC) of the antiresonance and resonance frequencies in a temperature range of -20°C to + 80°C vary with the change of the ratio of PbTiO 3  /PbZrO 3  when the mol fraction of the component Pb(Sn.sub.αSb 1   - .sub.α)O 3  is fixed. The results are shown in FIGS. 2 through 6. 
     The temperature coefficients(TC) were obtained by use of the following equations: ##EQU2## 
     FIG. 7 shows the changes of temperature coefficients (TC) when α = 1.00 and x = 0.05 as a function of the mol fractions of PbTiO 3  and PbZrO 3 . 
     In FIGS. 2 through 7, the solid line shows the result for the antiresonance frequency and the broken line shows the result for the resonance frequency. The positive and negative signs (+) (-) of TC in these figures have respectively the following meanings. The positive sign (+) means that the value of fomax (or famax) is found at a temperature higher than the room temperature (+20°C) or that the value of fomin (or famin) is found at a temperature lower than the room temperature (+20°C). The negative sign (-) has the opposite meaning of the positive sign. 
     From FIGS. 2 through 6, it will be seen that good points of the temperature coefficent are present in a wide compositional area where the mol fraction of PbZrO 3  ranges from 0.46 to 0.51. This shows that according to the present invention the piezoelectric ceramic materials having a good temperature coefficient can be obtained with ease when designing the filters, oscillators and the like having any desired piezoelectric characteristics such as ε s , kp and Qm. On the contrary, the ceramic compositions beyond the limits of the compositional area of this invention (i.e. α = 1) have large values on the positive side, as can be seen from FIG. 7. It is therefore impossible to select the composition having good temperature coefficient from these compositions. 
     FIG. 8 shows the relation between the degree of sintering and the contents of Sn and Sb. In this figure, the symbol () shows the composition which was converted into a fine structural sintered body and the symbol (□) shows the composition which was never converted into a sintered body. 
     From this figure, it will be seen that the compositional area where the fine structural sintered body can be obtained decreases with the decrease of the content of Sn. It will be also seen that if the content of Sb is more than 5 atomic percent when the content of Sn is zero, the fine structural sintered body is never obtained. 
     The area of the present composition has been described as being in the polygonal area defined by the points A, B, C, D, E and F in FIG. 1 for the following reasons. If the content of Pb(Sn.sub.αSb 1   - .sub.α)O 3  is less than 1 mol percent when 1/4 ≦ α ≦ 3/4, the temperature coefficient of the composition becomes great. Further, if the content of Pb(Sn.sub.αSb 1   - .sub.α)O 3  is more than 25 mol percent when 1/2 ≦ α ≦ 3/4, or more than 20 mol percent when 1/3 ≦ α &lt; 1/2, or more than 15 mol percent when 1/4 ≦ α &lt; 1/3, the electromechanical coupling coefficient of the composition becomes less than 20% and varies greatly by the heat aging. In addition, if the content of PbTiO 3  is more than 60 mol percent or if the content of PbZrO 3  is more than 69 mol percent, the electromechanical coupling coefficient of the composition becomes less than 20 %. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications are intended to be included within the scope of the following claims.