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. (C) 2003 Elsevier Science B.V. All rights reserved.