Processing of textured zinc oxide varistors via templated grain growth

Textured, dense zinc oxide varistors were successfully fabricated by Templated Grain Growth (TGG) technique. Rod-like, anisotropic ZnO particles (templates) were synthesized by homogeneous precipitation method. The templates are aligned in such a position where c-axes of the templates are parallel to the tape casting direction during the modified tape casting process. Since zinc oxide varistors are liquid phase sintered, addition of the templates to initial powder mixture does not result in constrained densification. The aligned zinc oxide templates grow anisotropically during sintering. (112¯0) and (101¯0) prismatic planes of the ZnO crystals (templates) grow faster than the other ZnO crystal planes. The growth of the templates results in texture development in zinc oxide varistors. As sintering temperature increases, fraction of textured grains in the microstructure increases. A template growth mechanism is also proposed for texturing zinc oxide varistors by TGG.