Influence of Ge and GeO2 on the microstructure and varistor properties of TiO2–Ta2O5–CaCO3 ceramics.

This study investigated the effect of elemental crystal Ge or/and GeO 2 doping on the microstructure and varistor properties of TiO 2 –Ta 2 O 5 –CaCO 3 varistor ceramics, which were prepared via the traditional ball milling–molding–sintering process. X-ray diffraction, scanning electron microscopy, scanning transmission electron microscopy-energy dispersive X-ray spectroscopy, scanning electron microscopy-energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy demonstrated that co-doping with Ge and GeO 2 changed the microstructure of TiO 2 –Ta 2 O 5 –CaCO 3 ceramics, thereby increasing the nonlinear coefficient and decreasing the breakdown voltage. The optimum doping concentrations of Ta 2 O 5 , CaCO 3 , Ge, and GeO 2 exhibited the highest nonlinear coefficient (α =14.6), a lower breakdown voltage ( E B =18.7 V mm −1 ), the least leakage current ( J L =10.5 μA cm −2 ), and the highest grain boundary barrier ( Φ B =1.05 eV). In addition, Ge and GeO 2 function as sintering aids, which reduce the sintering temperature because of their low melting points. [ABSTRACT FROM AUTHOR]