Effect of excess BaO and Nb2O5 on the grain coarsening of Ba(Ni1/3Nb2/3)O3 ceramics

The change of grain shape and resultant change in coarsening behavior of Ba(Ni1/3Nb2/3)O3 (BNN) ceramics which are widely used as microwave dielectrics were studied. During sintering at 1600 °C, the grains of the BNN specimen containing excess Nb2O5 were spherical and exhibited normal grain growth. With excess BaO, the grain shape was angular and abnormal grain growth was observed to occur. The normal and abnormal grain growth behavior can be explained in terms of diffusion controlled and 2-D nucleation controlled coarsening mechanism, respectively. An important point is that the grain shape is changed by a small compositional variation of the BNN specimen, and therefore the coarsening behavior is drastically changed.