Effects of B2O3 on the phase formation of Ba2Ti9O20 ceramic

The effects of B2O3 on the phase stability of Ba2Ti9O20 were investigated in this study. Differential thermal analysis (DTA) results of host materials, and with 5 wt.% B2O3 indicate that there is an endothermic peak at 840 °C. It is higher than 580 °C, the melting temperature of B2O3. This demonstrates that the eutectic liquid at this temperature. With the addition of 5 wt.% B2O3, the ceramic yielded a pure Ba2Ti9O20 phase at sintering temperature as low as 900 °C, without any solid solution additive, such as SnO2 or ZrO2. The benefit of B2O3 addition to the formation of Ba2Ti9O20 is apparently due to the eutectic liquid phase which accelerates the migration of reactant species. As the B2O3 addition increased to 10 wt.%, in addition to Ba2Ti9O20, small amounts of BaTi(BO3)2 and rutile TiO2 were found. Nevertheless, only pure Ba2Ti9O20 forms at sintering temperature higher than 1200 °C. BaTi(BO3)2 phase disappeared due to the evaporation of B2O3. The residue BaTiO3, subsequently, reacted with TiO2 and formed Ba2Ti9O20 phase.