Effects of additives on the phase formation and microstructural evolution of Ba2Ti9O20 microwave ceramic

Preparation of dense and phase-pure Ba2Ti9O20 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 Ba2Ti9O20 equilibrium phase boundary in the BaO–TiO2 system at high temperatures. It was reported that a small amount of solid solution additives is essential for the formation of a pure Ba2Ti9O20 phase, however, contradictory results were also addressed in the literature. In this study, TiO2, MnO, and ZrO2, were used to investigate the effects of additives on the densification, microstructural evolution and phase stability of Ba2Ti9O20. With the addition of 2.8 wt.% TiO2 and sintering at 1200 °C, ceramic yielded a pure Ba2Ti9O20 phase. It indicates that Ba2Ti9O20 is a nonstoichiometric compound, which can accommodate an excess amount of TiO2. With the addition of 4 wt.% ZrO2, phase pure Ba2Ti9O20 was obtained in the sintering temperatures of 1200 °C and 1300 °C. Results also indicated that MnO addition could promote the formation of Ba2Ti9O20, compared with that of pure host material, though pure Ba2Ti9O20 was not obtained. SEM microstructures are consistent with the observations in XRD patterns.