Phase equilibria in the system BaO–TiO2

The system BaO–TiO₂ is technically important because it contains multiple dielectric and ferroelectric phases, including the important BaTiO₃, which is one of the most widely studied dielectric perovskites owing to its dual piezoelectric and ferroelectric properties. The present work revises the subsolidus phase equilibria data by synthesizing previous phase equilibria data and new experimental results using high-temperature (600°–1300°C) and long-term (≤336 h) equilibration, coupled with analytical work based principally on room-temperature X-ray diffraction. The resultant phase diagram is given in both mole and weight percents, extending from the liquidus surface (not investigated) to absolute zero temperature (for inclusion of the previously excluded crystallographic and ferroelectric phase transformations). The major features include (1) correction of four eutectoid and three peritectoid reactions and corresponding temperatures, (2) indication of inferred partial solid solubilities, (3) clarification of the BaTiO₃ solid solubility homogeneity regions, and (4) specification of some invariant point compositions on the liquidus surface.