(Ge, GeO2, Ta2O5, BaCO3) co-doping TiO2 varistor ceramics.

The present study investigated the effect of co-doping with elemental crystal Ge or/and GeO 2 on the TiO 2 –Ta 2 O 5 –BaCO 3 varistor ceramic. Results showed that with the doping content of Ta 2 O 5 and BaCO 3 of 0.3 mol% and 0.2 mol%, respectively, the optimum doping content of 0.4 mol% Ge and 1.2 mol% GeO 2 exhibited the highest α value ( α = 12.1), lower breakdown voltage E B ( E B = 20.8 V mm − 1 ), lesser leakage current J L ( J L = 11.5 μA cm − 2 ), and highest grain boundary barrier Φ B ( Φ B = 0.93 eV). The microstructural analyses indicated that Ge–GeO 2 co-doping notably changed the TiO 2 –Ta 2 O 5 –BaCO 3 ceramic microstructure, increased α , and decreased E B . In addition, Ge and GeO 2 , which function as sintering aids, reduced the sintering temperature caused by the low melting point; the best sintering temperature was 1280 °C for TiO 2 –Ta 2 O 5 –BaCO 3 –Ge–GeO 2 ceramic. [ABSTRACT FROM AUTHOR]