Role of second phase in (Nb,Ce,Si,Ca)-doped TiO₂ varistor ceramics

A low-voltage TiO₂ varistor ceramics doped with Nb₂O₅, SiO₂, CeO₂ and CaCO₃ was systematically researched. The effects of different dopants on varistor voltage V_{1 mA} were investigated by orthogonal test method. SEM, XRD and EDAX were carried out to study the change of microstructure. The results show that there exist second phase on the surface of TiO₂ grains, which can facilitate an increasing varistor voltage. The second phase is proved to be Perrierite phase (Ce₂Ti₂Si₂O₁₁) by EDAX and the content varies with sintering temperature. It is suggested that the second phase segregates at the grain surface during sintering process and makes an insulating layer which result in a higher V_{1 mA}.