Semiconductive ceramic compositions with a nonlinear volt-ampere characteristic, and process for preparing coherent bodies of such compositions

A process for the fabrication of coherent bonded bodies of a semiconductive ceramic composition with a nonlinear volt-ampere characteristic, particularly well suited for use in varistors, which comprises:

• (a) providing a mixture of:
• (1) from about 86.000 to about 99.979% SrTiO.sub.3 in finely divided form;
• (2) from about 0.001 to about 5.000% of at least one metal oxide in finely divided form, for making the composition semiconductive, selected from the group consisting of Nb.sub.2 O.sub.5, Ta.sub.2 O.sub.5, WO.sub.3, La.sub.2 O.sub.3, CeO.sub.2, Nd.sub.2 O.sub.3, Pr.sub.6 O.sub.11, Dy.sub.2 O.sub.3, Y.sub.2 O.sub.3, and Sm.sub.2 O.sub.3 ;
• (3) from about 0.010 to about 5.000% of at least one other metal oxide in finely divided form, for improving the nonlinear volt-ampere characteristic of the composition, selected from the group consisting of V.sub.2 O.sub.5, Cr.sub.2 O.sub.3, CuO, Cu.sub.2 O, MoO.sub.3, and MnO.sub.2 ;
• (4) from about 0.010 to about 4.000% of at least one still other metal oxide in finely divided form, for improving the coherency of the bodies of the composition, selected from the group consisting of GeO.sub.2, ZnO, B.sub.2 O.sub.3, and PbO;
• and
• (5) a binder;
• (b) molding the mixture into bodies of desired shape under pressure;
• (c) firing the bodies in a temperature range of from about 1300.degree. to about 1500.degree. C. in a nonoxidative atmosphere;
• and
• (d) heating the fired bodies in a temperature range of from about 900.degree. to about 1300.degree. C. in an oxidative atmosphere.