Effects of B ₂ O ₃ on the Phase Stability of Ba ₂ Ti ₉ O ₂₀ Microwave Ceramic

Abstract

Preparation of dense and phase‐pure Ba 2 Ti 9 O 20 is generally difficult using solid‐state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition and a curvature of Ba 2 Ti 9 O 20 equilibrium phase boundary in the BaO–TiO 2 system at high temperatures. In this study, the effects of B 2 O 3 on the densification, microstructural evolution, and phase stability of Ba 2 Ti 9 O 20 were investigated. It was found that the densification of Ba 2 Ti 9 O 20 sintered with B 2 O 3 was promoted by the transient liquid phase formed at 840°C. At sintering temperatures higher than 1100°C, the solid‐state sintering became dominant because of the evaporation of B 2 O 3 . With the addition of 5 wt% B 2 O 3 , the ceramic yielded a pure Ba 2 Ti 9 O 20 phase at sintering temperatures as low as 900°C, without any solid solution additive such as SnO 2 or ZrO 2 . The facilities of B 2 O 3 addition to the stability of Ba 2 Ti 9 O 20 are apparently due to the eutectic liquid phase which accelerates the migration of reactant species.