Effects of additives on the phase formation and microstructural evolution of Ba2Ti9O20 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. It was reported that a small amount of solid solution additives is essential for the formation of a pure Ba 2 Ti 9 O 20 phase, however, contradictory results were also addressed in the literature. In this study, TiO 2, MnO, and ZrO 2 , were used to investigate the effects of additives on the densification, microstructural evolution and phase stability of Ba 2 Ti 9 O 20 . With the addition of 2.8 wt.% TiO 2 and sintering at 1200 °C, ceramic yielded a pure Ba 2 Ti 9 O 20 phase. It indicates that Ba 2 Ti 9 O 20 is a nonstoichiometric compound, which can accommodate an excess amount of TiO 2 . With the addition of 4 wt.% ZrO 2 , phase pure Ba 2 Ti 9 O 20 was obtained in the sintering temperatures of 1200 °C and 1300 °C. Results also indicated that MnO addition could promote the formation of Ba 2 Ti 9 O 20 , compared with that of pure host material, though pure Ba 2 Ti 9 O 20 was not obtained. SEM microstructures are consistent with the observations in XRD patterns.