Sintering process and microwave dielectric properties of Bi ₈TiO₁₄ ceramics

The formation of a homogeneous Bi₈TiO₁₄ phase was successfully achieved in a specimen calcined at 600°C. However, a Bi ₄Ti₃O₁₂ secondary phase also developed in specimens calcined at temperatures higher than 600°C, probably because of Bi₂O₃ evaporation. For specimens sintered above 800°C, a small amount of the Bi₈TiO₁₄ phase melted during sintering, with the liquid phase contributing to the densification of the specimens; however, Bi₄Ti₃O₁₂ and Bi ₁₂TiO₂₀ secondary phases were still formed in these specimens. The microwave dielectric properties of the Bi₈TiO ₁₄ phase were considerably affected by variations in the microstructure of the specimens. When the sintering temperature exceeded 825°C, the amount of secondary phases increased, and this decreased the density and Q×f values of the specimens. Bi₈TiO₁₄ ceramics sintered at 825°C exhibited promising microwave dielectric properties, with ε_r = 47.4, Q×f = 5370 GHz, and τ_f = -16.01 ppm/°C.