Subsolidus phase relations in the BaTiO3TiO2 system

Ba₆Ti₁₇O₄₀, Ba₄Ti₁₃O₃₀, BaTi₄O₉, and Ba₂Ti₉O₂₀ are the only compounds which were found to have a stability range in the subsolidus of the BaTiO₃TiO₂ system. BaTi₂O₅ and BaTi₅O₁₁, reported in other studies, apparently are not stable. The compound reported as Ba₂Ti₅O₁₂ appears to have been mistaken for Ba₆Ti₁₇O₄₀. X-Ray diffraction powder data are given for this phase which is monoclinic with a = 9.890, b = 17.117, c = 18.933 Å and β=98°42.6′. The phase formulated previously as BaTi₃O₇ is shown to be Ba₄Ti₁₃O₃₀ based on structural and density considerations, phase equilibria, and single crystal and powder X-ray diffraction data. This compound is orthorhombic with a = 17.072, b = 9.862, and c = 14.059 Å, probable space group, Cmca. An idealized structure for this phase is proposed. Ba₂Ti₉O₂₀ decomposes above 1300°C in the solid state to BaTi₄O₉ plus rutile. Single crystals were grown using BaF₂ as a mineralizer.