Sintering mechanism and microwave dielectric properties of Bi₁₂ TiO₂₀ ceramics

A homogeneous Bi₁₂TiO₂₀ phase was developed in a specimen that was calcined at 700°C without the formation of a secondary phase. A small amount of the Bi₁₂TiO₂₀ phase melted during sintering and assisted the densification of the specimen. The Bi ₂O₃ and Bi₈TiO₁₄ secondary phases were found in all specimens. All the specimens that were sintered at temperatures ≥775°C exhibited high relative densities above 98% of the theoretical density. The Q × f value of the Bi₁₂TiO ₂₀ ceramics was influenced by the grain size. The Bi ₁₂TiO₂₀ ceramics sintered at 800°C for 5 h showed promising microwave dielectric properties of ε_r = 41, Q × f = 10 400 GHz, and τ_f = -10.8 ppm/°C.