Preparation and dielectric properties of BaTiO₃-based X8R ceramics co-doped with BIT and CBS glass

The effects of Bi₄Ti₃O₁₂ (BIT) on phase purity and dielectric properties of BaTiO₃ (BT) ceramics have been investigated. Results show that BT samples doped with 1–3 mol% BIT adopt a single phase. However, secondary phase Bi₂Ti₂O₇ is observed when BIT content exceeds 3 mol%. Tetragonality and the Curie temperature (T _C) firstly increase and then decreases with an increase in BIT content. The 3 mol% BIT-doped BT ceramic sintered at 1,250 °C exhibits good dielectric properties of ε_r = 2,692, tan δ = 0.0152, ρ_v = 5.8 × 10¹² Ω cm, and the variation of dielectric constant as compared with that at room temperature is about −20 % at −55 °C and less than 11 % at 150 °C. It is found that the addition of calcium borosilicate glass (CBS) in BT-BIT ceramics can effectively lower the sintering temperature from 1,250 to 1,050 °C and further enhance the capacitance temperature stability. The permittivity decreases with an increase in CBS content from 1 to 10 wt%. Secondary phase BaBi₄Ti₄O₁₅ exists in the CBS doped BT-3BIT systems. All of CBS doped samples satisfy the X8R specification. Typically, the sample with 3 wt% CBS has ε_r = 1,789, tan δ = 0.0115, ρ_v = 9.67 × 10¹² Ω cm. The variation of permittivity as compared with that at room temperature is about −12 % at −55 °C and less than ± 11 % at 150 °C. The as-prepared materials have great potential as EIA X8R-type multilayer ceramic capacitors.