Effect of Bi₂O₃ doping on the dielectric properties of medium-temperature sintering BaTiO₃-based X8R ceramics

Medium-temperature sintering X8R ceramics were fabricated based on BaTiO₃-based ceramics with Bi₂O₃ additives. The effects of sintering aids Bi₂O₃ on crystalline structure and electrical properties of BaTiO₃-based ceramics were investigated. The sinterability of BaTiO₃ ceramics was significantly improved by adding Bi₂O₃, whose densification sintering temperature reduced from 1,260 to 1,130 °C. However, the dielectric constant (ε) of BaTiO₃-based ceramics doped with Bi₂O₃ was decreased dramatically. Both low ε phase Bi₄Ti₃O₁₂ and the decrease of the tetragonality (c/a ratio), which are demonstrated by XRD pattern, are resulted in the decrease of ε. The ε of samples doped with 5.5 wt% Bi₂O₃ was higher than the other doped samples. The substitution of Bi³⁺ for the Ba²⁺ in BaTiO₃ resulted in the increase of electrovalence (from +2 to +3) of A-site ion, so the attractive force between A and B (Ti⁴⁺) sites becomes stronger. Thus Ti⁴⁺’s polarization enhances, then ε was increased to some extent. The X8R BaTiO₃-based ceramics could be sintered at as low as 1,130 °C by doping 5.5 wt% Bi₂O₃ additives into the BaTiO₃-based ceramics, with a ε greater than 2,430 at 25 °C, dielectric loss lower than 1.3 % and temperature coefficient of capacitance <±15 % (−55–150 °C).