The effect of doping process on microstructure and dielectric properties of BaTiO3-based X7R materials

The effect of doping process on the dielectric properties, sintering behavior and microstructure were investigated on the BaTiO3-Nb2O5-Co3O4 ternary system ceramic. Temperature stable dielectric ceramics were obtained by different doping processes if only appropriate Nb5+ + Co3+ amount and Nb5+/Co3+ ratio were adopted. The dielectric constant was enhanced to the largest extent by nanometer oxide doping and the temperature characteristic satisfied the X7R specification. Two kinds of grains were observed in all the samples: matrix grains (BaTiO3) and the secondary phase grains (Ba6Ti17O40) formed by the incorporation of Nb5+ and Co3+ into BaTiO3 lattice and Ti4+ segregation. The matrix grains were about 1 mum in diameter and showed little grain growth with increasing temperature in all the doped samples, whereas the sizes of the secondary phase grains were strongly dependent on the doping process. The secondary phase formed liquid phase during firing, but the liquid phase contributed little to the densification of ceramics. (C) 2004 Kluwer Academic Publishers.