Abstract:
Ferroelectric ceramic compositions consisting essentially of quaternary solid solutions of Pb(Fe1/2.Nb1/2)O 3  --Pb(Zn1/3.Nb2/3)O 3  --PbZrO 3  --PbTiO 3 , the components of which are within a defined range of relative proportions, have substantially higher insulation resistance characteristics and substantially higher electromechanical coupling coefficient characteristics than prior art compositions. Additionally, the components within a more restricted range of relative proportions have the additional characteristic of a higher Poisson&#39;s ratio than prior art compositions.

Description:
This application is a continuation-in-part of our copending application Ser. No. 305,076 filed Nov. 9, 1972, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to ferroelectric ceramic compositions consisting of solid solutions of Pb(Fe1/2.NB1/2)O 3  - Pb(Zn1/3.Nb2/3)O 3  - PbTiO 3  - PbZrO 3  which are contained in a prescribed ratio range. 
     Ferroelectric ceramics utilized to construct ceramic filters, ultrasonic wave delay line elements, piezoelectric ignition elements and piezoelectric vibrating elements are required to be polarized readily when a DC voltage is applied and to have optimum electrical characteristics, as for example, high insulating resistances (IR), high electromechanical coupling coefficients (Kp), high dielectric constants (ε), and high Poisson&#39;s ratios (σ). 
     Heretobefore, ceramic compositions of the binary system, typically compositions of the PbTiO 3  -PbZrO 3  type, and ternary system, typically compositions of the Pb(Mg1/3.Nb2/3)O 3  -PbTiO 3  -PbZrO 3  type are generally used to prepare these ferroelectric ceramics. Generally, however, these compositions are difficult to fire and their range of firing temperature is narrow. Furthermore, it is difficult to obtain fired products of homogeneous composition. 
     For example, compositions of the PbTiO 3  -PbZrO 3  type are difficult to fire because lead oxide, one of the constituents, readily vaporizes during the firing step so that the resulting ceramics lack homogeneity and denseness and their dielectric and piezoelectric properties greatly depend upon the Zr:Ti ratio. 
     In addition to these drawbacks, compositions of the Pb(Fe1/2.Nb1/2)-PbTiO 3  -PbZrO 3  type have low insulation resistance and are difficult to polarize. Furthermore, with the compositions of the Pb(Zn1/3.Nb2/3)O 3  -PbTiO 3  -PbZrO 3  type the range of the compositions manifesting satisfactory electrical characteristics is extremely narrow. Also, in many applications of the ferroelectric ceramic compositions they are being used widely as a resonator of an energy-trapped type in electric wave filters for 1 to 10 MHz frequencies. In such applications, however, ferroelectric ceramic compositions having a Poisson&#39;s ratio of less than one-third essentially prevent the necessary energy trapping. 
     In the prior art it has been difficult to produce ceramic compositions having a Poisson&#39;s ratio of one-third, and it has been almost impossible to obtain ceramic compositions with a ratio of more than one-third. For example, an article in IRE, 1960 No. 2, pages 220 to 221, reports the highest Poisson&#39;s ratio for a ceramic composition as 0.328. Furthermore, the frequency variation in relation to the temperature variation (the temperature characteristics of the frequency) of an electric wave filter utilizing the prior art ceramic compositions has normally been about 100 ppm and in no instance better than 50 ppm with some superior materials. 
     Thus, none of these prior art compositions is suitable for obtaining ceramics with excellent electrical characteristics. 
     SUMMARY OF THE INVENTION 
     It is an object of this invention to provide improved ferroelectric ceramic compositions capable of eliminating various defects of the prior art compositions pointed out hereinabove. 
     In other words, it is the principal object of this invention to provide novel ferroelectric ceramic compositions which have wide ranges of firing temperature and can be utilized in the preparation of ceramics on a commercial scale which have high densities, high insulation resistances, high electromechanical coupling coefficients and large dielectric constants. 
     Another object of this invention is to provide novel ferroelectric ceramic compositions possessing improved characteristics for use in energy-trapped type filters, the Poisson&#39;s ratios of which are more than one-third. 
     Still another object of this invention is to provide compositions possessing excellent characteristics for electric wave filters together with better temperature characteristics at fixed frequencies. 
     According to this invention there are provided fired ferroelectric ceramic compositions consisting essentially of quaternary solid solutions of Pb(Fe1/2.Nb1/2)O 3  -Pb(Zn1/3.Nb2/3)O 3  -PbZrO 3  -PbTiO 3  in the relative proportions by mol % within the volume defined by the envelope enclosing the polygon area of the ternary diagrams of FIGS. 1-8 as sections in numerical order, the volume having the surface defined by a plurality of polygonal plane surfaces having apices corresponding to the numerals assigned thereto in FIGS. 1-8 as follows: 
     polygonal plane surfaces (1,5,9,10,8,4), (1,5,13,25), (25,39,5), (5,9,39), (39,48,9), (9,48,10), (10,49,48), (49,43,10,8), (8,43,14,4), (14,4,1), (1,14,13), (13,25,60,72), (25,39,72,86), (39,48,86), (48,49,86,90), (49,43,90), (90,71,43), (14,71,62,43), (14,13,60,62), (60,72,100,112), (72,86,112), (112,125,86), (86,125,123), (123,86,90), (123,111,90), (90,71.111), (71,62,111,102), (62,60,102,100), (100,112,133,140), (112,140,146), (112,125,146), (125,146,123), (123,146,149), (123,111,149), (111,149,135), (111,102,135), (102,100,135,133), (133,140,158,165), (140,146,165, 170), (146,149,170), (149,170,168), (149,135,168), (135,168,157), (135,133,157), (133,157,158), (158,165,177,183), (165,170,183), (183,184,170), (170,168,184), (168,184,181), (168,157,181), (157,181,177), (157,158,177) and (177,183,184,181) 
     where the numerals correspond to the compositional values designed in mol % in accordance with the following table of relative proportions: 
     
         ______________________________________Pb(Zn1/3 . Nb2/3)O.sub.3         Pb(Fe1/2 . Nb1/2)O.sub.3                      PbZrO.sub.3                              PbTiO.sub.3______________________________________1     1           1            69.3  28.75     1           1            49.5  48.59     1           19.8         39.6  39.610    1           29.7         39.6  29.78     1           29.7         49.5  19.84     1           19.8         59.4  19.813   10           1            70    1925   10           1            39    5039   10           20           20    5048   10           50           10    3049   10           60           10    2043   10           60           20    1014   10           10           70    1060   20           1            60    1972   20           1            29    5086   20           20           10    5090   20           60           10    1071   20           40           40    062   20           20           60    0100  30           1            50    19112  30           1            19    50125  30           10           0     60123  30           50           10    10111  30           40           30    0102  30           20           50    0133  40           1            40    19140  40           1            19    40146  40           10           10    40149  40           40           10    10135  40           20           40    0158  50           1            30    19165  50           1            9     40170  50           10           0     40168  50           30           10    10157  50           10           40    0177  60           10           20    10183  60           10           0     30184  60           20           0     20181  60           20           10    10______________________________________ 
    
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the accompanying drawings, 
     FIGS. 1-8 show phase diagrams of novel ferroelectric ceramic compositions in sections which respectively correspond to 1 mol %, 10 mol %, 20 mol %, 30 mol %, 40 mol %, 50 mol %, 60 mol % and 70 mol % of Pb(Zn1/3.Nb2/3)O 3  as one of the components of the compositions. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     As the starting materials, respective oxides Pb(Zn1/3.Nb2/3)O 3 , Pb(Fe1/2.Nb1/2)O 3 , PbZrO 3  and PbTiO 3  were weighed to form compositions of samples 1 to 192 referred to in the following Table 1. Each sample was mixed and pulverized for 15 hours in a wet-type pot mill lined with rubber and containing agate balls to obtain a homogeneous ceramic composition. The resulting composition was dried and calcined for 2 hours at a temperature of 800° to 900° C. Then the calcined composition was pulverized with a wet-type ball mill for 15 hours, and the pulverized compositon was dried. 
     1%, by weight based on the weight of the mixture, of an aqueous solution of polyvinyl alcohol was incorporated in each composition and the mixture was thoroughly kneaded with a mixer, suitably dried and pulverized. Particles having a grain size of 60 to 150 mesh were selected by means of a sieve. The resulting particles were put in a metal mold and molded with an oil pressure molding machine under a pressure of 1.5 tons/cm 2  to obtain a circular disc having a diameter of 22 mm and a thickness of 2 mm. The disc thus obtained was heated gradually to a temperature of 700° C in an air circulated electric furnace to remove polyvinyl alcohol and then fired in an alumina crucible for 1 hour. The firing temperature was varied from 1170° to 1360° C depending upon the composition. The temperature was raised at a rate of 300° C/hr. After maintaining the firing temperature at a desired value for a prescribed period, the heating element of the crucible was deenergized and the disc was cooled in the crucible. The resulting disc was lapped to a thickness of 0.6 mm and silver electrodes were printed and baked to the opposite surfaces of each disc. 
     Each disc was immersed in a silicon oil and polarized for 15 minutes at 140° C under a DC voltage of 3 KV/mm. After 24 hours, various electrical characteristics of the disc were measured to obtain the results shown in Table 1. The temperature characteristics of the frequency in Table 1 were calculated by the following equation: ##EQU1## 
     
                                           TABLE 1__________________________________________________________________________                                                 Temp.                  Firing                Curie    Characteristicssample Composition mol %                  temp.                      Kp          IR    temp.    of frequencynumber A   B   C    D   ° C                      (%) ε                              Qm  (× 10.sup.4 MΩ)                                        ° C                                            σ                                                 (ppm)__________________________________________________________________________1     1   1   69.3 28.7                  1320                      22.5                          421 284 1.22     1   1   59.4 38.6                  1310                      31.3                          469 233 3.13     1   9.9 59.4 29.7                  1300                      30.4                          534 318 5.0       0.3094     1   19.8         59.4 19.8                  1280                      25.5                          530 235 1.2   2965     1   1   49.5 48.5                  1310                      24.7                          436 211 1.36     1   9.9 49.5 39.6                  1300                      48.9                          817 248 2.0   3297     1   19.8         49.5 29.7                  1290                      26.4                          553 218 1.08     1   29.7         49.5 19.8                  1300                      24.8                          545 186 0.69     1   19.8         39.6 39.6                  1290                      24.7                          581 192 0.710    1   29.7         39.6 29.7                  1290                      28.4                          692 127 0.7   305*11   10  1   80   9   1310                      13.8                          282 123 0.8*12   10  10  80   0   1320                      11.5                          276 134 1.213    10  1   70   19  1320                      21.2                          386 173 1.814    10  10  70   10  1360                      21.9                          537 215 1.3       0.280*15   10  20  70   0   1300                      12.8                          358 151 1.616    10  1   60   29  1300                      33.3                          510 138 0.817    10  10  60   20  1360                      28.9                          534 176 0.8       0.31118    10  20  60   10  1360                      23.1                          534 214 1.2       0.306*19   10  30  60   0   1300                      14.4                          631 202 1.820    10  1   50   39  1290                      47.7                          853 97  3.821    10  10  50   30  1360                      36.9                          600 114 0.6   287 0.33522    10  20  50   20  1280                      36.3                          597 148 0.7       0.31723    10  30  50   10  1280                      28.7                          622 184 0.7       0.317*24   10  40  50   0   1280                      15.7                          674 234 1.425    10  1   39   50  1290                      29.5                          703 111 1.626    10  10  40   40  1300                      43.3                          1195                              120 1.8       0.38227    10  20  40   30  1300                      49.8                          762 97  0.8       0.33528    10  30  40   20  1300                      40.2                          658 133 0.6       0.33329    10  40  40   10  1260                      32.1                          651 174 0.4       0.314*30   10  50  40   0   1260                      16.4                          670 331 0.5*31   10  1   29   60  1280                      11.8                          419 83  2.432    10  10  30   50  1300                      24.6                          570 58  2.4       0.34133    10  20  30   40  1300                      30.3                          819 117 2.4       0.33834    10  30  30   30  1280                      41.5                          1546                              111 1.6   274 0.38435    10  40  30   20  1260                      43.5                          759 119 0.5       0.33736    10  50  30   10  1300                      33.1                          745 173 1.0       0.340*37   10  60  30   0   1300             0.03*38   10  10  20   6039    10  20  20   50  1280                      21.2                          484 47  1.840    10  30  20   40  1260                      24.5                          636 107 2.5       0.34241    10  40  20   30  1300                      31.8                          906 124 0.6       0.349                                                 -5842    10  50  20   20  1260                      37.5                          1878                              115 1.3       0.38043    10  60  20   10  1260                      32.8                          872 156 1.0       0.337*44   10  70  20   0   1260            less than                                   0.001*45   10  20  10   60*46   10  30  10   50  1260            less than                                   0.001*47   10  40  10   40  1260             0.00248    10  50  10   30  1260                      27.2                          741 82  2.0       0.33949    10  60  10   20  1240                      32.6                          1235                              238 1.3       0.350                                                 +75                                  less than*50   10  70  10   10  1260             0.001                                  less than*51   10  80  10   0   1240             0.001                                  less than*52   10  30  0    60  1260             0.001                                  less than*53   10  40  0    50  1260             0.001                                  less than*54   10  50  0    40  1240             0.001                                  less than*55   10  60  0    30  1240             0.001                                  less than*56   10  70  0    20  1240             0.001                                  less than*57   10  80  0    10  1220             0.001*58   20  1   70   9   1220                      19.2                          632 180 1.8*59   20  10  70   060    20  1   60   19  1300                      26.2                          497 165 1.161    20  10  60   10  1320                      27.0                          695 188 0.9       0.30262    20  20  60   0   1260                      20.8                          669 221 0.663    20  1   50   29  1290                      40.5                          685 137 1.064    20  10  50   20  1300                      36.1                          714 146 0.8       0.31265    20  20  50   10  1300                      31.6                          733 160 0.8       0.31666    20  30  50   0   1280                      20.7                          718 252 2.067    20  1   40   39  1300                      55.3                          1070                              84  1.468    20  10  40   30  1300                      50.0                          796 92  1.2       0.33469    20  20  40   20  1280                      43.1                          774 123 1.0       0.31670    20  30  40   10  1280                      33.7                          730 160 0.6       0.31571    20  40  40   0   1260                      21.1                          771 324 0.672    20  1   29   50  1290                      28.5                          699 121 1.873    20  10  30   40  1280                      40.8                          1023                              136 2.4   304 0.35874    20  20  30   30  1300                      45.5                          1608                              110 2.0       0.37875    20  30  30   20  1260                      47.4                          892 106 0.5   228 0.33576    20  40  30   10  1260                      36.7                          820 150 0.5       0.324*77   20  50  30   0   1280             0.03*78   20  1   19   60  1300                      13.6                          380 253 3.079    20  10  20   50  1300                      26.2                          563 244 3.1       0.34080    20  20  20   40  1260                      27.0                          753 213 2.7       0.34881    20  30  20   30  1280                      38.1                          1175                              134 2.4       0.363                                                 -5882    20  40  20   20  1260                      52.4                          2144                              107 1.4       0.39083    20  50  20   10  1240                      41.4                          1026                              122 0.5       0.334*84   20  60  20   0   1260             0.005*85   20  10  10   6086    20  20  10   50  1280                      24.3                          602 258 3.0       0.32687    20  30  10   40  1260                      38.5                          628 265 2.6       0.33688    20  40  10   30  1240                      27.7                          907 191 1.7       0.33789    20  50  10   20  1260                      37.1                          1507                              128 1.8       0.365                                                  -690    20  60  10   10  1240                      42.8                          1410                              192 1.1       0.367*91   20  70  10   0   1280             0.02                                  less than*92   20  20  0    60  1260             0.001*93   20  30  0    50  1260            less than                                   0.001                                  less than*94   20  40  0    40  1240             0.001*95   20  50  0    30  1240            less than                                   0.001*96   20  60  0    20  1220            less than                                   0.001*97   20  70  0    10  1220            less than                                   0.001*98   30  1   60   10  1300                      18.9                          507 155 1.1*99   30  10  60   0   1300                      17.5                          785 261 1.6100   30  1   50   19  1280                      30.3                          600 137 1.5101   30  10  50   10  1280                      28.8                          865 177 1.3   0.314102   30  20  50   0   1260                      22.3                          824 230 0.6103   30  1   40   29  1280                      47.3                          882 109 1.7104   30  10  40   20  1300                      40.6                          917 115 1.0   0.334105   30  20  40   10  1260                      33.0                          888 153 1.4   0.318106   30  30  40   0   1240                      22.2                          923 180 0.8107   30  1   30   39  1290                      42.1                          1333                              103 1.5108   30  10  30   30  1280                      61.4                          1855                              81  0.9   0.377                                            -10109   30  20  30   20  1260                      44.8                          958 110 0.8   0.337110   30  30  30   10  1240                      33.5                          932 141 1.2   0.333111   30  40  30   0   1240                      20.5                          906 249 0.6112   30  1   19   50  1270                      23.7                          727 152 2.5113   30  10  20   40  1260                      33.9                          856 180 2.9       0.340114   30  20  20   30  1260                      36.7                          1319                              141 2.5       0.371115   30  30  20   20  1240                      58.0                          2271                              89  2.6   220 0.384116   30  40  20   10  1240                      42.4                          1039                              120 0.7       0.340*117  30  50  20   0   1260             0.005*118  30  1   9    60  1260                      12.5                          466 258 2.8119   30  10  10   50  1260                      20.7                          516 331 2.4       0.306120   30  20  10   40  1260                      23.0                          677 284 2.2       0.320121   30  30  10   30  1240                      31.9                          951 124 3.2       0.335122   30  40  10   20  1260                      40.2                          1586                              140 1.8       0.371                                                 +32123   30  50  10   10  1240                      33.5                          1575                              121 0.7       0.370*124  30  60  10   0   1260             0.009125   30  10  0    60  1200                      24.0                          798 243 0.8*126  30  20  0    50  1190                      19.8                          901 248 0.6                                  less than*127  30  30  0    40  1240             0.001                                  less than*128  30  40  0    30  1240             0.001                                  less than*129  30  50  0    20  1240             0.001                                  less than*130  30  60  0    10  1220             0.001*131  40  1   50   9*132  40  10  50   0   1240                      18.6                          865 221 1.1133   40  1   40   19  1260                      39.6                          689 183 1.2   246134   40  10  40   10  1280                      24.3                          919 188 2.1       0.328135   40  20  40   0   1240                      22.0                          876 189 0.5136   40  1   30   29  1270                      55.5                          1483                              97  1.3137   40  10  30   20  1280                      40.0                          1068                              109 1.2       0.342138   40  20  30   10  1240                      29.4                          1025                              152 1.4       0.321*139  40  30  30   0   1240                      19.4                          979 197 0.6140   40  1   19   40  1260                      31.3                          1251                              128 2.3141   40  10  20   30  1260                      42.1                          1458                              113 2.5       0.381142   40  20  20   20  1240                      55.5                          1863                              98  1.4   222 0.348143   40  30  20   10  1200                      28.6                          1181                              136 1.1       0.338*144  40  40  20   0   140              0.03*145  40  1   9    50  1240                      18.8                          588 177 2.4146   40  10  10   40  1240                      26.4                          718 217 2.7       0.326147   40  20  10   30  1200                      29.8                          1074                              174 2.2       0.331148   40  30  10   20  1200                      42.2                          1780                              128 1.8       0.358                                                 +20149   40  40  10   10  1240                      32.3                          1557                              124 1.1   0.328*150  40  50  10   0   1240             0.003*151  40  10  0    50  1260                      13.6                          487 291 0.6*152  40  20  0    40  1220             0.01                                  less than*153  40  30  0    30  1220             0.001                                  less than*154  40  40  0    20  1220             0.001                                  less than*155  40  50  0    10  1220             0.001*156  50  1   40   9157   50  10  40   0   1270                      23.6                          666 128 2.3158   50  1   30   19  1220                      39.2                          853 125 2.4159   50  10  30   10  1200                      23.2                          909 179 2.5*160  50  20  30   0   1230                      18.1                          807 281 2.0161   50  1   20   29  1200                      47.8                          1548                              115 2.1162   50  10  20   20  1200                      51.8                          1422                              99  2.4   225 0.330163   50  20  20   10  1220                      28.3                          1175                              145 1.5*164  50  30  20   0   1230                      19.5                          1019                              249 3.0165   50  1   9    40  1200                      26.8                          977 160 3.0166   50  10  10   30  1180                      31.7                          1070                              163 2.7167   50  20  10   20  1200                      36.4                          1909                              129 1.1            +20168   50  30  10   10  1200                      29.9                          1457                              112 1.3*169  50  40  10   0   1200             0.01170   50  10  0    40  1220                      21.6                          614 294 0.6*171  50  20  0    30  1190                      19.1                          901 248 4.4                                  less than*172  50  30  0    20  1240             0.001                                  less than*173  50  40  0    10  1220             0.001*174  60  1   30   9*175  60  10  30   0   1200             0.003*176  60  1   20   19177   60  10  20   10  1240                      55.5                          1863                              99  1.4*178  60  20  20   0   1180             0.002*179  60  1   9    30180   60  10  10   20  1180                      37.9                          1797                              111 2.5181   60  20  10   10  1220                      24.5                          1271                              149 1.6*182  60  30  10   0   1220                      21.9                          1232                              25  0.4   140183   60  10  0    30  1230                      20.8                          785 207 3.0   205184   60  20  0    20  1190                      23.8                          1332                              175 2.8*185  60  30  0    10  1200             0.006*186  70  0   20   10                                  less than*187  70  10  20   0   1200             0.001*188  70  0   10   20*189  70  10  10   10*190  70  20  10   0   1200             0.002*191  70  10  0    20  1170                      27.8                          1888                              150 0.2   165*192  70  20  0    10  1190                      24.4                          1187                              177 0.2   152__________________________________________________________________________ Remarks: A Pb(Zn1/3  . Nb2/3)O.sub.3 B Pb(Fe1/2  . Nb1/2)O.sub.3 C PbZrO.sub.3 D PbTiO.sub.3 Kp Electro-mechanical coupling coefficient ε Dielectric constant IR Insulating resistance σ Poisson&#39;s ratio MΩ 10.sup.6 
    
     As can be noted from Table 1, samples not marked with a symbol * are the compositions included in the scope of this invention. Ceramics prepared by these compositions showed an excellent electro-mechanical coefficient (Kp), a large dielectric constant (ε) and a high insulation resistance (IR). 
     Also, as seen from Table 1, according to the novel ceramic compositions of the present invention, high Poisson&#39;s ratios of more than 0.333 were obtained over a wide range. An extremely high value of 0.390 was obtained with Sample No. 82. 
     Further, as for the temperature characteristics of the frequency, excellent characteristics such as -(minus) 6 ppm with Sample No. 89 and -(minus) 10 ppm with Sample No. 108 were obtained. It should be understood that, even with resonators containing quartz which are considered to possess excellent temperature characteristics of the frequency, the best obtainable value is in the order to ppm at most. 
     In Table 1 those marked with a symbol *, that is Sample Nos. 11, 12, 15, 19, 24, 30, 31, 37, 38, 44-47, 50-59, 77, 78, 84, 85, 91-99, 117, 118, 124, 126-132, 139, 144, 145, 150-156, 160, 164, 169, 171-176, 178, 179, 182, 185-192, are not included in the scope of this invention. 
     More particularly, Samples 38, 45, 59, 85, 131, 156, 174, 176, 179, 186, 188 and 189 cannot form fired ceramics. The insulation resistances of the ceramics prepared from Samples 37, 44, 46, 47, 50-57, 77, 84, 91-97, 117, 124, 127-130, 144, 150, 152-155, 169, 172, 173, 175, 178, 185, 187 and 190 are lower than 0.2 × 10 4  MΩ  and the IR-temperature characteristics of these samples were also poor. The electro-mechanical coupling coefficients (Kp) of the ceramics prepared from Samples 11, 12, 15, 19, 24, 30, 31, 58, 78, 98, 99, 118, 132, 139, 145, 151, 160, 164, and 171 were less than 20% which are too low for practical use. Further, ceramics prepared from Samples 182, 191 and 192 have relatively low Curie temperatures not suitable for practical use. 
     In this invention, instead of using PbO and Fe 2  O 3 , it is also possible to use peroxides or hydroxides of these metals such as Pb 3  O 4 , Fe(OH) 3  which are convertible to oxides by heat decomposition. It is also possible to use a mixture of an oxide, and a peroxide or a hydrogen. It should also be understood that the zirconium oxide utilized in this invention may contain a small quantity of hafnium since hafnium is not separable from zirconium oxide for industrial use. 
     As above described, the novel ceramic compositions of this invention consisting essentially of quaternary solid solution of Pb(Fe1/2.Nb1/2)O 3  -Pb(Zn1/3.Nb2/3)O 3  -PbZrO 3  -PbTiO 3  and containing the constituents at a definite ratio can be fired at lower temperatures than well known ceramic compositions in a wider range of firing temperatures. Moreover, the quantity of evaporation of Pb during the firing step is small so that it is possible to produce dense and homogeneous ferroelectric ceramics. Since the resulting ceramics have high insulation resistance and high diamagnetic field property they can be readily polarized, for example in about 15 minutes under a voltage of 3 KV/mm. Moreover, the ceramics containing the novel compositions have dielectric constant ε varying over a wide range of 500 to 2000, and have high values of electro-mechanical coupling coefficient (Kp). Consequently, the novel compositions can provide ferroelectric ceramics having desired characteristics for any application. 
     In order to produce a ceramic filter of an energy-trapped type, the Poisson&#39;s ratio of the ceramic compositions needs to be more than one-third and Poisson&#39;s ratios of more than one-third over a wide range are obtainable by the present invention. 
     Thus, the ceramic compositions of the present invention, particularly the compositions in the volume defined by a plurality of polygonal surfaces having apecies corresponding to the following sample numbers, when used as ceramic filters of an energy-trapped type, have little spurious oscillation (unwanted oscillation) and have excellent filter characteristics. 
     Referring to FIGS. 1-8, the plurality of polygonal surfaces defining those compositions having a Poisson&#39;s ratio greater than one-third are designated by: (32,48,49,43,36,21), (21,32,79,68), (32,48,87,79), (48,90,87), (48,49,90), (49,43,90), (43,36,83,90), (36,21,68,83), (68,79,113,104), (79,87,121,113), (87,90,123,121), (90,83,110,123), (83,68,104,110), (104,113,141,137), (113,121,148,141), (121,123,148), (123,143,148), (123,110,143), (110,104,137,143), and (137,141,148,143). The polygonal surfaces are drawn by connecting points in each of the parentheses. The polygonal surfaces three-dimensionally constitute a volume, and some of them are on the sectional planes as illustrated in FIGS. 2-5 in dotted lines. 
     Also, because the ceramic compositions of the present invention have an excellent advantage in the temperature characteristics of the frequency, an electric wave filter utilizing these materials can be very accurate with little variation in the frequency due to temperature. 
     Furthermore, since the ceramic compositions of the present invention form in entirety a solid solution, combinations of different characteristics according to needs can easily be obtained. 
     In FIGS. 1-8 of the accompanying drawings which show phase diagrams of novel ferroelectric compositions respectively containing 1 mol %, 10 mol %, 20 mol %, 30 mol %, 40 mol %, 50 mol %, 60 mol % and 70 mol % of the constituent Pb(Zn1/3.Nb2/3)O 3 , reference numerals 1-184 show compositions 1 to 184 shown in Table 1. FIGS. 1-8 are drawn by sectioning a trigonal pyramid a predetermined mol % of Pb(Zn1/3.Nb2/3)O 3  in parallel with the bottom surfaces of the trigonal pyramid, which trigonal pyramid has a triangular bottom surface with apices of PbZrO 3 , PbTiO 3  and Pb(Fe1/2.Nb1/2)O 3  and the remaining apex of Pb(Zn1/3.Nb2/3)O 3 . The manner of sectioning is simply for the convenience of explaining the invention, and it is understandable that the section can be indicated by any of the mol quantities of PbZrO 3 , PbTiO 3  or Pb(Fe1/2.Nb1/2)O 3  instead of Pb(Zn1/3.Nb2/3)O 3  .