Abstract:
A dielectric ceramic composition having a composition represented by the formula 
     
       xBaO-yNd.sub.2 O.sub.3 -z(Ti.sub.1-m Zr.sub.m)O.sub.2 
     
     wherein x+y+z=1.00 
     
       0&lt;m≦0.25 
     
     and x, y, and z are in the molar ratio region surrounded by the points a, b, c, and d which are represented by the following x-y-z coordinates: 
     
       ______________________________________ 
     
     x                  y      z______________________________________a       0.15           0.12   0.73b       0.15           0.18   0.67c       0.05           0.18   0.77d       0.05           0.12   0.83______________________________________

Description:
BACKGROUND OF THE INVENTION 
     This application is a continuation-in-part of our copending application Ser. No. 451,929, filed Dec. 21, 1982, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a dielectric ceramic composition having a high dielectric constant and a low degree of temperature dependency of dielectric constant, which can be prepared at a relatively low firing temperature. 
     The following systems have hitherto been known as temperature-compensating dielectric porcelain compositions: 
     MgO-TiO 2  -CaO system 
     La 2  O 3 .2TiO 2  -CaTiO 3  -2MgO.TiO 2  system 
     TiO 2  -BaTiO 3  -Bi 2  O 3  -La 2  O 3  system 
     However, these compositions have low dielectric constants and are disadvantageous in that baking temperatures for their production are relatively high. Moreover, Pd cannot be used as internal electrodes for laminated condensers formed from Bi 2  O 3  -containing compositions because Bi 2  O 3  attacks Pd electrodes. 
     SUMMARY OF THE INVENTION 
     The primary object of this invention is to provide a dielectric ceramic composition free from such disadvantages as mentioned above, that is, a composition of sufficiently high dielectric constant, containing no Bi 2  O 3 , which can be produced by a lower temperature firing. 
     Another object of this invention is to provide a dielectric ceramic composition exhibiting minimum temperature dependency of dielectric constant. 
     Thus, this invention provides a dielectric ceramic composition having a composition represented by the formula 
     
         xBaO-yNd.sub.2 O.sub.3 -Z(Ti.sub.1-m Zr.sub.m)O.sub.2 
    
     wherein, x+y+z=1.00, 
     
         0&lt;m≦0.25 
    
     and x, y, and z are in the molar ratio region surrounded by the points a, b, c, and d which are represented by the following x-y-z coordinates: 
     
         ______________________________________x                  y      z______________________________________a       0.15           0.12   0.73b       0.15           0.18   0.67c       0.05           0.18   0.77d       0.05           0.12   0.83______________________________________ 
    
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing is a ternary system composition diagram showing the proportion ranges of essential components of the composition of this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The dielectric ceramic composition of this invention consists mainly of xBaO, yNd 2  O 3 , and z(Ti 1-m  Zr m )O 2 , wherein x+y+z=1.00, 0&lt;m≦0.25, and x, y, and z are in the parallelogram formed, as shown in the drawing, connecting the pairs of points a-b, b-d, d-c, and c-a. 
     Reasons for limiting the proportions of the main components of the present invention to said region are explained below with reference to the drawing. In A-region (A-, B-, C-, and D-regions are out of the scope of this invention), the raw material mixtures are difficult to sinter, the sintering is insufficient, and the compositions exhibit decreased values of Q. In B-region, the temperature coefficient of capacitance is excessively large on the negative side, being unsuited for practical use. In C-region, said temperature coefficient is excessively large on the positive side and the dielectric constant is undesirably low. In D-region, the temperature coefficient is excessively large on the positive side, the dielectric constant is undesirably low, and the sintering is extremely difficult. The dielectric constant becomes low when Nd 2  O 3  is less than 12 mol% or is more than 18 mol%. In the range of 0&lt;m≦0.25, the sintering is easy; increasing m shifts the temperature coefficient toward the positive side; in this case, a composition of high dielectric constant is obtained in the vicinity of NPO by selecting a proper composition. When m exceeds 0.25, the sintering becomes difficult and Q decreases. 
     The composition of this invention may contain, besides the essential components mentioned above, at least one member selected from oxides of manganese, chromium, iron, nickel, and cobalt in amounts of 0.05-1.00% by weight of the total weight of the main components, in terms each of MnO 2 , Cr 2  O 3 , FeO, NiO, and CoO. These additives have an effect of improving sintering properties of the raw material mixture. The total content of these additives, when less than 0.05% by weight, has no such effect, and when exceeding 1.00% by weight, results in a decrease in dielectric constant. 
     This invention will be illustrated in more detail by the following examples, which are however not to be construed to limit the scope of this invention. 
     EXAMPLE 1 
     Raw materials, BaCo 3 , Nd 2  O 3 , TiO 2 , and ZrO 2 , were mixed in different compounding ratios so that the fired products might contain components in proportions as shown in Table 1. The resulting mixtures were calcined in air at 1000° C. for 2 hours. The calcined materials were pulverized, mixed with an organic binder, and shaped into thin circular pieces of 16 mm in diameter and 0.6 mm in thickness by applying a molding pressure of 3 ton/cm 2 . Samples Nos. 1-36 were obtained by firing these places for one hour at the individual temperatures shown in Table 1. 
     Electrical properties of these samples were determined by plating both faces of each specimen with a silver electrode, and using a YHP digital LCR meter (Model 4274A, supplied by YHP, Tokyo, Japan) and YHP Q-meter (Model 4342A, supplied by YHP, Tokyo, Japan) under measuring conditions of temperature 25° C., voltage 1.0 vrms and frequency of 100 KH Z  (except 1 MH Z  for Q value). The temperature coefficient of capacitance was determined on the basis of the value of capacitance by the following equation 
     
         Temperature coefficient=(C.sub.85 -C.sub.25)/(C.sub.25 ×60)×10.sup.6 (ppm/°C.) 
    
     preparation conditions for the samples and results of the measurement are shown in Table 1. 
     
                                           TABLE 1__________________________________________________________________________                        Dielectric PropertiesComponent                         Temperatureproportion (mol %)                Coefficient ofSample    x  y   z           Firing Temp.                             capacitanceNo. BaO  Nd.sub.2 O.sub.3      (Ti.sub.1-m Zr.sub.m)O.sub.2              m  (°C.)                        ε.sub.s                          Q  (ppm/°C.)__________________________________________________________________________1   15 17  68      0.10                 1270   83                          6000                             -432   15 17  68      0.15                 1290   80                          5500                             -153   15 17  68      0.20                 1300   76                          5000                               04   12 18  70      0.05                 1250   74                          8300                             -255   12 18  70      0.07                 1250   73                          7600                              -46   12 18  70      0.10                 1250   72                          6800                             +157   10 18  72      0.07                 1250   72                          7500                             -308   10 18  72      0.10                 1250   68                          8700                             -159   12 16  72      0.10                 1250   74                          7800                             -4010  12 16  72      0.15                 1250   72                          7500                             -2211  12 16  72      0.20                 1270   67                          7000                              -512  10 16  74      0.15                 1270   68                          7500                             -3013  10 16  74      0.20                 1290   64                          7200                             -1514  10 16  74      0.25                 1310   61                          7000                               015  7.5  16.5      76      0.10                 1250   81                          6500                             -3216  7.5  16.5      76      0.15                 1270   79                          6200                               017  5  17  78      0.15                 1290   92                          6000                             -17518  5  17  78      0.20                 1310   88                          6000                             -15419  5  17  78      0.25                 1330   85                          5400                             -13620  10 12  78      0.15                 1300   78                          5000                             -11821  10 12  78      0.20                 1310   74                          4500                             -9622  10 12  78      0.25                 1330   70                          4000                             -7523  15 12  73      0.10                 1290   74                          6000                             -6124  15 12  73      0.15                 1310   68                          5800                             -2525  15 12  73      0.20                 1330   66                          5200                             -1026  15 18  67      0.10                 1270   85                          6000                             -5027  15 18  67      0.15                 1290   80                          5300                             -1228  15 18  67      0.20                 1310   77                          5000                             +1129  5  18  77      0.07                 1290   65                          7000                             -9030  5  18  77      0.10                 1310   60                          6500                             -7531  5  12  83      0.15                 1310   87                          4500                             -12532  5  12  83      0.20                 1330   82                          4100                             -15733  12 14  74      0.10                 1270   70                          7100                             -10034  12 14  74      0.15                 1270   68                          6700                             -7835  7.5  14  78.5    0.05                 1300   80                          6000                             -13536  7.5  14  78.5    0.10                 1310   77                          5700                             -111__________________________________________________________________________ 
    
     
                                           TABLE 2__________________________________________________________________________                               Dielectric Properties                      Amount        TemperatureComponent proportion       of   Firing   Coefficient ofSample    x  y   z               Additive                           temp     capacitanceNo. BaO  Nd.sub.2 O.sub.3      (Ti.sub.1-m Zr.sub.m)O.sub.2              m  Additive                      (wt %)                           (°C.)                               ε.sub.s                                 Q  (ppm/°C.)__________________________________________________________________________37  7.5  16.5      76      0.15                 MnO.sub.2                      0.05 1260                               78                                 6500                                    -538  7.5  16.5      76      0.15                 MnO.sub.2                      0.10 1250                               80                                 6300                                    -1039  7.5  16.5      76      0.15                 MnO.sub.2                      0.20 1240                               64                                 6600                                    -2740  10 16  74      0.25                 Cr.sub.2 O.sub.3                      0.40 1270                               57                                 7200                                    -2941  15 17  68      0.20                 NiO  0.80 1270                               51                                 6100                                    -3242  12 18  70      0.10                 FeO  0.20 1250                               70                                 6500                                    -11243  10 12  78      0.15                 CoO  0.50 1270                               77                                 5000                                    -110__________________________________________________________________________ 
    
     As shown in Table 1, all the samples have a high dielectric constant, small temperature dependency of capacitance, and a Q-value sufficient for practical use and can be prepared by firing at relatively low temperatures. 
     EXAMPLE 2 
     Samples Nos. 37-43 were prepared and measured for dielectric properties in the same manner as in Example 1 except that MnO 2 , Cr 2  O 3 , Feo, Nio, or CoO was added to raw materials, BaCO 3 , Nd 2  O 3 , TiO 2 , and ZrO 2 , so as to give the baked product component proportions shown in Table 2. The results are shown in Table 2. 
     As can be seen from Table 2, the firing temperature could be lowered by addition of MnO 2 , Cr 2  O 3 , FeO, or CoO.