Microstructure and dielectric properties of Ag-BaTiO3 composite ceramics

Di-phase composite ceramics based on BaTiO3 with 5 vol% of Ag filler have been prepared by sintering the mixture of powders at temperatures above the silver melting point (1000 °C-1300 °C/2 h). As predicted by finite element calculations, the addition of metallic particles should produce a field concentration in some regions of the BaTiO3 matrix and therefore, an enhanced dielectric response with respect to pure BaTiO3. The role of oxygen vacancies on the dielectric relaxation mechanisms of Ag-BaTiO3 composites has been investigated. The sintering temperature of 1200 °C provided optimized ceramics with excellent dielectric properties, i.e. with low losses (tanδ < 3%) and room temperature permittivity measured at 50 kHz exceeding 6500 (and above 13,000 at the Curie temperature), as result of a good densification (94% relative density) and a synergy effect of the metallic particles inclusions and ceramic grain size in the range of ≈1 μm, where BaTiO3 has a well-known maximum of its permittivity.